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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
1 - 100 of 1137 results
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Mitigation of Safety Risks in Pursuing Mega 3D Seismic Survey in Former Battle Field Area
Authors A.M. Alkandari, K. Chakraborty, L. Al-Fehaid and H. Al-KhaldiSummaryThe Gulf War conflict of 1991 turned Partitioned Zone (PZ) of the Kingdom of Saudi Arabia and the State of Kuwait into a high-risk area with regards to Unexploded Ordnance(UXO) and Explosive Remnants of War (ERW). A large national and international effort has previously cleared UXO/ERW from most of the country, but to date UXO/ERW is still found because of the dynamic nature of the environment. During 2014–16, a high resolution, multi-azimuth 3D seismic Survey was completed utilizing 168,000 UniQ channels, with 20 DX-80 vibrators, shooting flip flop with four fleets 24/7, covering approximately 4,612 km2 (5,346 km2 including the 2 zippers). The survey was planned to satisfy the geological objectives, safety and security threats, and restricted access due to oil production facilities. An innovative two-phase risk-based approach was implemented to ensure personnel and operational safety while maximizing seismic production. A total of 551 days was spent for UXO/ERW identification, with a total of 82 UXO found and destroyed. The seismic acquisition project of more than 100 vehicles and 600 personnel was completed without any incidents or accidents and a high standard of verification was maintained throughout the project execution.
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Sedimentology, Diagenesis and Reservoir Quality of the Bentiu Formation in the Fula Sub-Basin, Muglad Basin, Sudan
More LessSummaryThe factors controlled reservoir quality in the Bentiu Formation are: 1) sediments depositional processes; 2) diagenetic processes; and 3) burial depth. As a result, the porosity and permeability of the studied samples vary significantly due to these factors. Based on a detailed sedimentological and petrographical analyses, the following general conclusions are made:
- The coarser to medium grained sandstones with lower total clay content have higher porosity and permeability than sandstones with highest clay content, suggesting that clay content is a major control in porosity and permeability.
- Quartz overgrowths, pyrite, siderite and iron oxide together with kaolinite and chlorite are the major cement minerals observed in the studied Bentiu sandstones. These minerals migrate/ disaggregate into pore spaces and throats, thereby causing a decrease in porosity and permeability.
- With increasing the burial depth, the mounts porosity and permeability decrease due to compaction and cementation (quartz overgrowths).
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Polarization Analysis and 3D Patterns for the Six Basic Seismic Moment Tensors
Authors H. Li, S. Greenhalgh and X. LiuSummaryPolarization is an important property of seismic waves that specifies the direction of particle motion. A full polarization measurement system in 3D space could be exploited for passive seismic event detection, seismic direction finding, and wavefield filtering. Seismic sources with different moment tensors will cause polarization differences which could in principle be used for focal mechanism analysis, even for moment tensor inversion. Here, we simulate the 3D vectoral seismic data set for the six basic moment tensor sources which are then used for polarization analysis. Then, we analyze the polarization patterns (azimuth and inclination angle variations) for P and S waves over the ground surface for a buried source, taking into account polarity changes. The results show that the seismic waves from the different basic moment tensor sources have dissimilar polarization characteristics. Such patterns could be exploited to invert for the hypocenter location and the moment tensor of the source. We next consider an actual 3C borehole microseismic field data set and extract the polarization angle. It is clear that a much wider aperture monitoring system is required to sense rapid and/or appreciable angular changes in the polarization vector for effective moment tensor inversion.
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It Is Rough to Be a Fracture – But How Rough?
Authors K. Bisdom, M. Zhang, T. Phillips, N. Forbes Inskip, N. Kampman and A. BuschSummaryFrom its initiation to propagation, opening and closing, a fracture is under continuous pressure as a result of coupled hydromechanical and geochemical processes. The combination of these processes, including for example dissolution and precipitation, karstification and shearing, leads to complex fracture surface geometries that resemble anything but the parallel plate representation that is typically assumed in fracture network models to calculate aperture and permeability.
Using a novel workflow for characterizing fracture roughness and aperture from core plugs, we aim to gain new insights into how different mechanical and chemical processes impact fracture roughness and how the resulting fracture surface geometry influences permeability of shear fractures in shales, to assess the leakage potential of natural fractures in CO2 storage site caprocks.
We make use of a digital microscope and python-based image processing and roughness quantification. The roughness parameters are correlated to permeability data to derive empirical relations for fracture flow modelling based on a known mineralogy and bedding orientation. The results are used to populate caprock leakage risk models in a joint industry research project for CO2 storage, but the methodology can also be applied to naturally fractured reservoirs.
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Seismic Random Noise Attenuation via Unsupervised Sparse Machine Learning
More LessSummaryIn the field of exploration geophysics, seismic waves received by near-surface geophones are usually corrupted by random noise, which degrades the performance of the following seismic exploration process, such as imaging and inversion. Therefore, random noise attenuation plays an essential step in seismic data processing. In this research, we propose a denoising autoencoder to remove random noise from seismic records. Different from traditional autoencoders that constrain representations, the denoising autoencoder trys to attain appropriate representations by changing the reconstruction criterion, which allows neural network to capture the true seismic wave composition and then attenuate random noise. Compared with the other methods, real data shows that the proposed method achieves better performance in terms of the weak signal preservation and random noise attenuation.
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3D Errors in 2D Seismic Images: Analysis and Prediction of Errors Due to a Thrust Fault
Authors J. Harding and J.E. OmañaSummarySeismic data collected in complex land settings is often two-dimensional (2D). The data is then processed in 2D, and these 2D images are ideally representative of the subsurface beneath the profile. This may not be the case, however, if the subsurface has complicated three-dimensional (3D) structure and lateral heterogeneity, like in fold-and-thrust belt settings. In order to quantify these 3D errors in 2D seismic images, we carried out a synthetic case study using a 3D model based on the Caipipendi block in Bolivia, where a target horizon lies beneath a thrust fault. We compare results from illumination studies and 2D migrated images with predicted errors due to a single thrust fault. Illumination studies reveal that seismic energy can reflect off subsurface boundaries kilometers outside of the crosslines. The target in the crosslines consequently has migrated depth errors of tens to hundreds of meters. The thrust fault explains the majority of the errors, both in the lateral direction perpendicular to the 2D plane, and in depth. Our thrust fault error prediction equations have the potential to correct for errors in a seismic strikeline due to a cross-dipping thrust fault and can be incorporated into uncertainty analysis and risk assessment.
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Stratigraphic Features of Impregnated Sand within the Ratawi Shale and Their Hydrocarbon Prospectivity in Bahrah, Kuwait
Authors P.K. Nath, P.K. Nath, S.F. Al-Rashidi, S.K. Bhukta, S.K. Singh and A.A. Wadi Al-EneziSummaryThe lower Cretaceous reservoirs are very good producers in various structures of Kuwait. The Ratawi Formation, which is of lower Cretaceous, consists of Ratawi Limestone Member in its lower section and Ratawi Shale Member above it. The reservoirs in both have been successfully drilled in many parts of Kuwait. In Bahrah area a few wells have produced oil from the sands of the Ratawi Shale Member. These sands are discrete, thin and limited areal extent but have good porosity. Though they have the hydrocarbon potential additional efforts in terms of understanding their nature of deposition, entrapment, play, etc., are required to explore them further. The main challenges are to establish presence of thin reservoir, its geometry and distribution within thick Shale section. Sequence Stratigraphy, mapping these sands in acoustic impedance volume and using spectral decomposition, it is inferred that migratory and vertically stacked channels in Bahrah area of Kuwait deposit them. The channel course is apparently from the north to south instead of the current understanding of the northwest origin. The potential of these sands can be well realized by invoking stratigraphic play concept in exploration and development. This paper focuses on the coarser clastic deposits within Ratawi Shale Member.
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Optimization of Safe Distance in Pursuing Seismic Data Acquisition through Oil Fields and Populated Areas
Authors I. Hakam, A.W. Sadeqi, A. Al-Kandari and K. ChakrabortySummaryThe present paper will focus on a mega single sensor 3D seismic survey, where different environments that needed to be covered. These includes producing oil fields, oil installations, refinery's, cities, farms and construction sites. Due to these changing as well as challenging environments, a safety standard had to be adopted to support vibrator and explosive sources for safe and successful completion of the project. Peak Particle Velocity (PPV) surveys were conducted using the DIN 4150 German Standard as a reference whenever the seismic operation approached to any oil field infrastructure, populated area or any possible vulnerable hazards. A total of 666 PPV measurements were conducted in multiple environments within the seismic survey boundary. Based on these tests a set of optimum possible safety distances were determined to oil installations, residential structures, construction sites and other infrastructures to ensure that the quality of the final seismic imaging is optimized and survey objective is achieved.
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Seismic Subtle Sequence Boundary Identification, High-Frequency Sequence Framework Establishment and Lithologic Trap Exploration
By X. ShaSummaryFocusing on the facts that the type and accuracy of sequence boundaries identified on seismic is lower than that on logging and the established sequence framework cannot favorably meet the needs of lithologic reservoir exploration, a method of seismic subtle sequence boundary identification and high-frequency sequence framework establishment was proposed based on logging-seismic time-frequency matching analysis and seismic all-reflector tracking. Technically, it involves the time-frequency analysis of logging, logging calibration to seismic and seismic all-reflector tracking based on seismic time-frequency analysis, and the relationship of seismic reflection cycles matching to logging was obtained and the high-resolution spatial sequence framework was established. The sequence boundaries within this framework not only have clear geological meanings of sedimentary cycles, but also have high resolution. It can effectively identify the subtle sequence boundary which is difficult to be recognized by conventional method, and favorably meet the accuracy requirements for lithologic trap identification and description in sequence stratigraphy study. The Jurassic in the western margin of Turpan-Kumul Basin demonstrated the application of this method and good result was achieved. It is helpful for tapping the potential of seismic interpretation, high-resolution sequence stratigraphy study and lithologic reservoir exploration.
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An Integrated Machine Learning Platform for Multi-Scale and Multi-Domain Applications in Geosciences
More LessSummaryIn this paper, I introduce a comprehensive machine learning framework that combines the benefits of complementary algorithms. The user can design his/her own workflow through easy combination of a large number of Python libraries. This approach is addressed to many different types of applications in geosciences at variable spatial scale and for different purposes. I discuss briefly two applications: the first is a case of litho-facies classification of well log data; the second concerns the construction of probabilistic maps of oil distribution using multidisciplinary geophysical data.
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Permeability of Porous Limestones under a Wide Range of in Situ Conditions
More LessSummaryA fundamental understanding of fluid flow in carbonate formations is of importance in many crustal processes. We investigated the influence of inelastic compaction on permeability of Purbeck, Indiana and Leitha limestones, with porosities ranging from 14 to 30%. Permeability measured during hydrostatic and triaxial compression showed comparable evolutions under relatively high effective pressures. With the development of shear-enhanced compaction, a permeability reduction by up to factor 3 was observed in all cases. Overall, our data revealed smaller reduction of permeability due to inelastic compaction in limestone than that previously observed in sandstone. Indiana and Purbeck limestones are double-porosity medium with significant proportions of macropores and micropores. In the absence of a percolative backbone of macropores, micropores exert a significant influence its permeability. In this context, inelastic compaction by cataclastic pore collapse, preferentially of macropores, is not an efficient way to reduce significantly the permeability. Our data on Leitha limestone also suggest that the development of compaction bands in such macroporous, high permeability carbonate does not have a significant impact on fluid flow.
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Application of Walkaway-VSP Based on Joint Observation by DAS and Geophones in Northwest China
Authors C. Zhidong, G. Yu and Y. LiSummaryGreat advancement in Distributed Acoustic Sensing (DAS) technique has contributed to its wide application in the borehole seismology for some geophysical purposes, such as structural analysis, parameter estimation and reservoir prediction. Tarim Basin, as one of the most petroliferous basin in the northwest China, has been known for the notoriously deep well conditions, including high pressure and high temperature. In this context, VSP applications are greatly limited by the bearing capacity of conventional geophones. Alternatively, DAS technique displays its superiority in good adaption to complex environment. In order to target oil and gas reservoirs with deep burial and complex features, a Walkaway-VSP technique is employed to confront the undesired well conditions, which is based on joint observation by DAS and geophones. This study first compares VSP data respectively recorded by DAS and geophones, then discusses the processing method, and finally obtains a high-precision imaging profile, which lays a solid foundation for the later comprehensive geological research.
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Elastic Anisotropic Full Waveform Inversion Using Probabilistic Petrophysical Constraints
Authors O.C. Aquino de Aragão and P. SavaSummaryFull waveform inversion (FWI) works by iteratively minimizing an objective function that measures the misfit between observed and predicted data in the least-squares sense. However, FWI suffers from significant problems. First, the inversion solved by gradient techniques may not lead to the globally optimal solution. Second, all wave propagation mechanisms are not adequately considered if one does not assume a stiffness tensor structure that truly represents the subsurface. Third, depending on the parameterization used for inversion, elastic properties may be coupled and updates of one parameter may impact others, an effect known as interparameter crosstalk. Additionally, some combinations of model parameters can be lithologically implausible, and not represent feasible lithological units. We derive anisotropic subsurface models using elastic FWI and explicitly impose petrophysical penalties to recover models consistent with the seismic data as well as with the petrophysical context in the area. This methodology reduces the potential negative impact of local minima, mitigates interparameter crosstalk artifacts, and avoids geologically implausible models. We define this penalty using probability density functions derived from petrophysical information. The proposed FWI objective function leads to robust anisotropic models that represent plausible lithologies, while at the same time leading to data predictions consistent with the observations.
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A Calculation Method of PS-Wave Static Correction by Combining First Arrival Wave and Surface Wave
More LessSummaryMulti component technology has been used in a number of oil exploration area in China. However, due to the propagation characteristics of the PS-wave, the first arrival wave of the PS-wave data collected is not easy to identify, so the PS-wave static correction processing is a difficult problem in multi component exploration. The traditional PS-wave static correction values calculation is to multiply the PP-wave static correction values by an empirical coefficient, but this method will produce the phenomenon of periodic jump , so it is not accurate. Generally, the P-wave records contain clear information of the first arrival wave and surface waves, and there is a very important relationship between surface wave and shear wave. Therefore a new calculation method of PS-wave static correction by combining first arrival wave and surface wave is presented to improve the accuracy of PS-wave static correction. Applications on real data show very high performance of the proposed method in this paper.
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Fine Characterization of Volcanic Rock Morphology by Walkaway VSP Technique
Authors X. Xingrong, T. Yancan, S. Qin, X. Junfa and L. MengliSummaryBecause the wave impedance of volcanic rocks is not much different from that of surrounding rocks, it is difficult to accurately describe the morphology of special lithologic bodies such as volcanic rocks. In order to solve the problem, the method of accurately describe the morphology of volcanic rocks using Walkaway-VSP data was studied. The volcanic rocks and surrounding rocks of the Walkaway-VSP data have obvious wave impedance interfaces. The processing produce based on the principle of “fidelity” is adopted to protect the effective information of volcanic rock reservoirs and provide a good data foundation for the accurate description of volcanic rocks. Santanghu Basin in Tuha Oilfield in western China is a typical tight oil enrichment area in China. Through fine processing and interpretation of Walkway-VSP data of M68(oil well name)in the area, high-resolution and high-fidelity Walkway-VSP longitudinal wave imaging results are obtained, which not only determine the shape and plane distribution characteristics of source rock and volcanic rock reservoirs, but also finely identify their lithologic interfaces in the longitudinal direction, and achieve good fine characterization effect.
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Geological Modeling and Development Strategy Optimization of Fractured-Caved Carbonate Reservoirs
More LessSummaryNaturally fractured-caved carbonate reservoirs in China have some distinctive characteristics: developed multi-scale fractures, vugs and caves, no moveable oil in pores, poor reservoir connectivity and much difficult to develop. How to effectively develop this kind of reservoirs is a major challenge. This paper presents the corresponding development strategy optimization for different reservoir patterns of this kind of reservoirs.
Based on understanding of geological study and dynamic characterization, typical reservoir patterns are identified and established. Corresponding different reservoir simulation models are built for different reservoir patterns. Then reservoir simulation are used for the development strategy optimization for different reservoir patterns. Finally, the optimization results are applied to the enhanced oil recovery of a fractured caved carbonate reservoir in China.
This paper has been successfully applied to a heterogeneous fractured caved reservoirs in China, which provides a reliable foundation for the effective development of this kind of reservoir. Also the method can be used for development strategy optimization study of other kinds of carbonate reservoirs worldwide.
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Automated Real Time Path Planning for Land Seismic Survey Field Design
Authors M. Caporal, C. Tsingas, A. AlShuhail and G. BlacquiéreSummaryIdeal survey designs provide evenly sampled data complying with predefined specifications in terms of offset and azimuth distributions, as well as fold and trace density. Orthogonal geometries are conventionally preferred but frequently difficult to implement in the field. Geographic, topological and environmental factors may limit the practical implementation of traditional designs and ad-hoc adjustments may be necessary during operations. Restricted or inaccessible areas and obstacles in the field are, in fact, not uncommon and potentially result in poor coverage.
This abstract presents two automated approaches to land vibroseis survey design that guarantee adequate survey attributes and avoid spatial discontinuities in the recorded data, even where adverse field conditions are present. The two methods are based on the reorganization of regular (centralized) and irregular (decentralized) source acquisition grids, respectively. Both methods provide a practical acquisition pre-plan for seismic crews. We tested these techniques on a real terrain map featured by a substantial amount of inaccessible areas due to the presence of steep sand dunes.
The focus of this study is on the source geometry. On the receiver side, the survey geometry is assumed not to be affected by the presence of the obstacles. This is the case in most practical applications.
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Mems Based 3-C Borehole Gravity Meter Development
More LessSummaryA MEMS (Micro-Electro-Mechanical) based 3-C borehole gravity meter is being developed in China for mineral and hydrocarbon exploration. The 3-C borehole gravity meter is composed of a three-axis gravity sensor chip based on deep silicon etching technique, high precision capacitive displacement sensing and weak signal detection circuitry. The gravity sensing chip is a silicon-based integrated spring-mass block system. The silicon wafer is etched by micro-nanofabrication technique to form a high collimation groove. The size of the gravity detecting mass block in the sensitive unit plays a decisive role in the thermal noise level of the instrument. Deep silicon processing technique can produce thicker silicon mass block (500 µm), which can obtain larger mass block in the same area compared with traditional silicon surface processing technique (10–100 µm). The out diameter of the final tool will be 50 mm with 5 μGal resolution, 20 μGal repeatability, 10,000 mGal measurement range, 155℃ temperature and 100 MPa pressure rating. Apart from 3-C MEMS gravity sensor, a 3-C fluxgate magnetic sensor is also added to downhole tool. This allows us to measure both 3-C gravity field and 3-C magnetic field downhole simultaneously, and conduct joint inversion of both downhole gravity and magnetic data.
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Diagenesis, Depositional Model and Stratigraphic Evolution of the Margalla Hill Limestone, Southeast Hazara
More LessSummaryThe purpose of this abstract is to evaluate the depositional and diagenetic model of Early Eocene Margalla Hill Limestone. Four sections of subjected formation have been studied for samples collection and outcrop measurements. Detailed microscopic analysis of thin sections enabled us to characterize the subjected limestone into three microfacies. By studying the microfacies, I became able to interpret the depositional model, diagenetic variations, primary and secondary porosity and sequence stratigraphy of the formation. Syndiagenetic changes in the subjected limestone make it available to act as potential reservoir and these changes include physical and chemical compaction, neomorphism and dissolutioning etc. Moreover, by analyzing the described microfacies, I made able to say that Margalla Hill Limestone was being deposited on carbonate shelf from inner ramp to outer ramp setting. Sequence stratigraphic analysis represents deposition on high stand system tract (HST).
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Integrated Reservoir Geology, Seismic Facies, and Production Studies to Determine the Potential of Well Development Area
Authors A. Zhumabekov, Z. Liu, X. Wei, X. Chen and V. PortnovSummaryWell operation accounts for potential geological and technological capabilities is one of the important factors affecting the efficient production of hydrocarbon reserves. The main tool for substantiating the technological efficiency of drilling new wells is a geological hydrodynamic network model of the field of development object. However, the process of creating a development plan is time-consuming, and the result, in certain cases, ambiguous. To address potential well development area in terms of residual oil, new integrated analysis workflow summarized based on the results which directly related to a reliable study of the sedimentation medium, in particular microfacies and various reservoir property data and production behavior of wells. The new workflow includes the following steps: 1. Study a well re-completion potential and idle wells conditions 2. Establish favorable phase areas for static analysis 3. Carry out dynamic parameters with an application of seismic inversion 4. Identify potential sites constrained by seismic, geological studies and initial production of the oil field 5. Provide suggestions in a new well development plan. This workflow has been applied successfully for the selection of potential zones for drilling new wells at the preliminary design stage, before creating a production network for the reservoir site model.
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Elastic Full-Waveform Inversion with Geologic Information for Tilted TI Media
Authors S. Singh, I. Tsvankin and E. Zabihi NaeiniSummaryHigh-resolution velocity models generated by full-waveform inversion (FWI) can be effectively used in seismic reservoir characterization. However, FWI in elastic anisotropic media is hampered by the nonlinearity of inversion and parameter trade-offs. Here, we propose a robust way to constrain the inversion workflow using per-facies rock-physics relationships derived from borehole information (well logs). The advantages of the facies-based FWI are demonstrated on a 2D elastic TTI (transversely isotropic with a tilted symmetry axis) model with substantial structural complexity. In particular, the tests show that our algorithm improves the spatial resolution of the inverted medium parameters without using ultra-low-frequency data required by conventional FWI.
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Geostatistical Interpolation Constrained by Lithofacies
More LessSummaryGeostatistical technologies, which include two-point geostatistics (TPS) and multiple-point geostatistics (MPS), are significant in both geological modelling and geophysical inversion. However, TPS is incapable to characterise complex geological structures, due to the dependency on the variogram. When using MPS in the simulation of the continuous variables such as velocity, the calculation and memory burdens are heavy. We integrate TPS with MPS to release these issues. Based on kriging theory, we present a geostatistical interpolation strategy constrained by the lithofacies probability distribution, which is obtained by MPS. The proposed approach utilizes the advantages of TPS and MPS simultaneously. The model test illustrates the effect of the method on depicting complicated geological structure.
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Homogenization of Hydro-Mechanical Coupling in Shale Matrix
More LessSummaryShale matrix is the main gas storage space, so the development of its Hydro-Mechanical coupling (HM) model is important to macroscopic HM simulation in shale gas reservoir. At microscopic scale, shale matrix is composed of organic and inorganic matter, while the mechanical properties of these two media are quite different, and both gas storage type and transport mechanism are also different in these two media, thus we need to develope different microscale models to describe the HM process in shale matrix. However, microscale models cannot be straightly applied to macro simulation due to their huge calculation cost. In this paper, an efficient upscaling method based on homogenization theory is developed for the HM process in shale matrix, which can accurately represent the microscale characteristics of organic and inorganic matter in macroscale simulations. Firstly, shale matrix is assumed as a heterogeneous poroelastic medium composed of organic and inorganic matter, and according to different storage type and transport mechanism of real gas in these two media, the microscale HM model is developed. Then, the microscale HM model is homogenized to obtained the equivalent macroscopic HM model for shale matrix. Lastly, the accuracy of the proposed method is proved through a numerical examples.
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Optimising Nanoparticles Mixture for Enhanced Oil Recovery
More LessSummaryIn this study, a combined nanofluid based on mixing Silicon-oxide, Aluminum oxide nanoparticles with 2D-smart nanosheet (MAS2DSN) for enhanced oil recovery is developed. The current single nanofluid flooding method for tertiary or enhanced oil recovery is inefficient, especially when used with low nanoparticle concentration. In this work, we show the potential of mixing nanoparticles with two-dimensional smart nanosheets in one patch as a C-EOR agent. The combination of a Mixture of Aluminum-Silicon nanoparticles with 2D-Smart Nanosheet (MAS2DSN) is used to reduce the IFT and altering the wettability of the sandstone core samples even at low concentrations. The IFT decreases up to 0.16 %, and the contact angle measurements show that the wettability of sandstone is changed from the oil-wet to the water-wet in the presence of MAS2DSN. The laboratory core-flooding experiments were conducted in the sandstone core samples saturated with module oil (20 cP). Stable MAS2DSN nanofluid is applied in core-flood experiments using Al2O3, SiO2, and 2DSN at concentrations of 0.05, 0.05 and 0.005 % respectively, resulting in a 22.9% increase in the oil recovery. This work exposes new opportunities for oil production by using a mixture of nanoparticles.
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Gpr Full Waveform Frequency-Space Domain Modeling by the Full Spectral Methods
More LessSummaryAccurate differentiation matrices operators by the full spectral method have been applied to the temporal and spatial domains of the transverse electric (TE) and transverse magnetic (TM) modes of the GPR full waveform. By Fourier transform, these operators are simply complex frequency and wavenumber which must be sampled appropriately to produce accurate results. This full spectral method contrasts with the pseudo-spectral method that transforms only a component (either the time or space) to the Fourier domain and leaves the second component in its regular domain. The finite difference approach supplies its approximate differentiation matrices operator in time and space domains thus leading to inherent truncation error. Convolution of the differentiation matrices operator with the medium parameter is performed; and the inversion of the system of linear equations produce the accurate GPR full waveform modeling results for different permittivity models.
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Initial Wave Impedance Modeling Method Based on Plane-Wave Destruction
More LessSummaryInitial model is critical to the model-based wave impedance inversion method, and its accuracy directly influences the convergence speed of inversion and the accuracy of inversion results. In this paper, the initial wave impedance modeling method based on plane-wave destruction (PWD) is proposed, the wave impedance information is extrapolated by using of the predict relationship between the traces which is derived from the plane-wave destruction equation, and the Tikhonov regularization is introduced to improve the stability and noise resistance ability of the method. No longer like the traditional modeling methods which need the fine horizon and fault interpretation results, the method in this paper is a seismic data-driven modeling method, the initial model which has a good consistency with the geological rules can be directly established by using of seismic data and well-log properties. The effectiveness of the method is demonstrated by model data test and field data application.
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Mineral Prospecting for Copper-Molybdene Ores in Northern Kazakhstan Using Electromagnetic Sensing and Induced Polarization Technology (EMS-IP)
Authors A. Belova, Y. Davydenko, D. Gurevich, A. Bashkeev, S. Bukhalov and P. VeekenSummaryGeoelectric techniques are applied to identify geobodies in the shallow subsurface (<1km) that correspond to commercial ore deposits (copper-molybdene) in Kazakhstan. A combined CSEM and Induced Polarisation method is chosen to delineate anomalies in the underground. Resistivity and polarisation effects prove diagnostic. The workflow comprises steps like: EM acquisition, quality control and data preconditioning, inversion, interpretation and Principle Component Analysis. Inversion processing is done via a finite elements method solving the Cole-Cole formula simulating Maxwell’s equations. 1D inversion results serve as input for the 3D inversion. Principle Component Analysis (n-dimensional clustering and distance weighting) and computation of composite geoelectric parameters enhance the discrimination power. EM anomalies are circular (hydrothermal injection feature) and/or elongate in shape. Fracture zones and faults provide conduits/barriers and govern hydrothermal processes. Faulting in part controls the outline of the segmented IP anomalies. Three shallow well locations were proposed based on the EMS-IP data. Two of these boreholes demonstrate elevated polarisation phenomena: copper-molybdene metal ore in MN17 and pyrite enrichment in MN16. The mapped geobodies based on EM anomalies give complementary information on volume and distribution of the mineral resources. EMS-IP is a cost-effective investigation tool that deserves more attention in geoscience projects.
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Mud-Roll Removal in Shallow Water Marine Data Using the Curvelet Transform
Authors F. Ahmed, E. Verschuur and C. TsingasSummaryMud-roll comprises of dispersive seismic waves that propagate along the unconsolidated sediment layers at the sea floor in shallow water marine environments, where the water depth is normally less than 30 m. Mud-roll’s characteristics are spatially variable, i.e. the dispersion properties change from one shot to another across a seismic survey area. These complex kinematic properties make noise elimination very challenging using conventional seismic processing workflows. Our proposed method is a hybrid, Curvelet transform-based workflow that takes advantage of conventional seismic processing filtering to estimate the noise components, followed by the Curvelet transform that attenuates the residual noise energy that is difficult to remove with a conventional subtraction algorithm. In this paper, we illustrate the proposed Curvelet transform-based workflow using both synthetic and field data and demonstrate its effectiveness.
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Artificial-Lift Method Screening for One of the Southwestern Iranian Oil Field Based on Fuzzy Logic Approach
Authors H. Asaadian and M. Nazari SaramSummaryThe choice of an artificial lift method in fields that have been faced with declining production has always been a challenge. Therefore, in this paper, by designing a two-stage screening process and using fuzzy logic approach, it is attempted to select the most accurate method for one of the southwest Iran squares. Fuzzy logic will make the ranking system more accurate and more sensitive to the operating conditions of artificial lift methods. By the method ranking with this screening procedure, Electrical Submersible Pump (ESP) and Sucker Rod Pump (SRP) are selected as the priorities.
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Full-Bandwidth FWI
Authors T. Kalinicheva, M. Warner and F. ManciniSummaryWe have run FWI to 100 Hz on raw field data from a deep-water marine towed-streamer dataset. We show that the results are similar to, and are broader bandwidth than, conventionally processed PSDM images. FWI removes multiples and ghosts from the raw data, and can produce a full-bandwidth PSDM reflectivity image in a few days without conventional processing or migration.
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Separation of LS-Epithermal Gold Veins Deposit Alterations by Geophysics in Chucotka Region
By E. ErmolinSummaryA number of epithermal gold-silver deposits are located within Okhotsk-Chukotka volcanic belt (Far East of Russia). LS-epithermal veins with the thickness of several meters can contain up to several hundred tons of gold. The search of covered veins is a complicated task for exploration and it is difficult to solve it without geophysics. The example of successful application of audiomagnitotelluric method in Chukotka region was presented by author. As the result of all data analysis the geophysical prospecting criteria were suggested. Unfortunately, not every found vein is commercial. To increase the chance of finding a new deposit the author set the task to define additional prospecting criteria. The induced polarization (IP) method was used to achieve this goal. The main result of the investigation is that the instrument for separation of alterations types was suggested. The chargeability anomalies at 0.31 Hz and 15 mV/V amplitude are connected with illite chlorite alterations of a deposit core. Illite chlorite alteration of the core deposit is also characterized by high resistivity (up to 2000 Ohm-m) and low magnetic susceptibility. The zones of illite and kaolinite alterations surrounding the deposit core are characterized by reduced electrical resistivity (from 50 to 300 Ohm-m).
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Immiscible Water Alternating CO2 Displacement Efficiency in Layered Water Wet Porous Media
Authors D. Al-Bayati, A. Saeedi, M. Myers, C. White, Q. Xie and M.M. HossainSummaryIn this work, a laboratory test to investigate the influence of permeability heterogeneity and ensuing crossflow on the recovery performance of immiscible water alternating CO2 injection was performed. The results reveal the negative impact of heterogeneity in the vertical direction on ultimate oil recovery from layered cores. Contrary to our previous conclusions about continuous immiscible CO2 flooding, it possible to observe that the crossflow to negatively affect the RF of immiscible WAG in layered samples. This contradiction may suggest that WAG flooding would achieve a stable frontal advance in each layer in non-communication layers.
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Slope Estimation by Convolutional Neural Networks
More LessSummaryLocal dip field has have been widely used in geophysical applications, such as structure prediction, seislet transform, trace interpolation and denoise. The plane-wave destruction (PWD) is the common method to estimate the local slope. However, the PWD is sensitive to strong noise. It is not easy to estimate an accurately local slope from noisy data by PWD algorithm. To estimate an accurate slope from noisy seismic data, we have proposed an architecture based on deep learning (DL). The architecture contains two sections: the convolutional and deconvolutional sections. The conventional section can learn the local features and the deconvolutional section constructs the output using the learned feature to match the target. Numerical tests on two examples demonstrate that the proposed method can obtain a relatively accurate dip field from noisy data.
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Triaxial Induction Tools Responses in Layered Arbitrarily Anisotropic Medium
More LessSummaryDue to different sedimentary environments, the realistic formation shows different electrical anisotropic characterizations. In general, only electrical anisotropy in layered unrotated media is considered, which is not always available in the practical application. With the widespread availability of multi-component induction logging technology, it is willing to solve more complicated electrical anisotropy problems. Therefore, it is important to introduce a universal algorithm applicable for arbitrary electrical anisotropic media. A fast forward algorithm, based on dyadic Green’s function, is proposed to compute the triaxial induction responses under arbitrary anisotropic media. Anisotropic dip and azimuth are introduced to further characterize the complicated electrical anisotropy. Numerical simulations proved the robustness of the algorithm, and illustrated the responses under different electrical anisotropic situations. It can be concluded that anisotropic dip and azimuth could impose great influences on the triaxial induction logging responses. Some important phenomena can be observed, for example, there exist critical borehole dip and critical anisotropic dip in the rotated uniaxial and biaxial media, and the crosscouping magnetic components, Hxy (Hyx) and Hyz (Hzy), are closely related to the anisotropic azimuth. The proposed algorithm could well make up the deficiency of traditional method and reduce the uncertainties of resistivity interpretation.
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3D Characterization of Pore Microstructure and Implications for Flow Transport Property of Tight Reservoirs
More LessSummaryUnconventional hydrocarbons have been considered as important complementary resources to conventional resources, which have been intensely investigated in recent years. Pore microstructure, especially of tight reservoirs, has significant effect on flow capacity, storage capability and recovery efficiency. A comprehensive understanding of pore microstructure is crucial for the prediction of transport property, and thus provides some basis for the evaluation of tight oil potential area. Three-dimensional features of pore network were studied by X-ray CT data analysis, where geometrical and topological parameters were calculated. On the basis of these quantitative analyses, numerical simulations were conducted for demonstrating transport capability.
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Deep Learning for Salt Body Detection: A Practical Approach
Authors B. Consolvo, B.P. Consolvo, P. Docherty and J. UwaifoSummaryInterpreting salt bodies in the subsurface is a challenging manual task that can take weeks to complete. Obtaining accurate picks of salt is very important, because errors in the placement of salt can result in severe degradation of the seismic image. To meet the challenges of speeding up imaging workflows and retaining accurate salt picks, we evaluate three deep learning approaches: a 2D window-based convolutional neural network, a 3D window-based convolutional neural network, and finally a 2D “U-Net” approach. A 3D seismic volume from the deep-water field Julia in the Gulf of Mexico was used to test these approaches. The Julia field has complex salt structures with overhangs and inclusions, and the thickness of salt can reach up to 5 km. The U-Net architecture proved to be the most accurate of the three methods tested, predicting the placement of salt at 98% accuracy, as compared to the human interpretation. Beyond accuracy, U-Net also proved to be the fastest, requiring only 3.5 hours to predict salt on the 3D seismic volume. The results presented here along with other recent studies of deep learning for salt interpretation represent a clear shift in the seismic interpretation workflow.
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A New Acoustic Assumption That Mitigates the S-Waves Artifacts in Orthorhombic Media
Authors M.M. Abedi and A. StovasSummaryApplication of acoustic orthorhombic media can be considered as a modern standard in industrial 3D seismic data processing and modeling stages. However, the presence of significant S-wave artifacts that are associated with the conventional acoustic anisotropic media harms any application that need pure P-wave propagation. Accordingly, we propose a new acoustic assumption for orthorhombic media that mitigates the S-waves artifacts by zeroing the S-waves velocities along the symmetry planes. The accuracy of the new approach compares well with the conventional approach, but the new approach further complicates the governing equations. Noticing the algebraic complexity of the eikonal equation obtained in the new acoustic orthorhombic media, we also propose a rational approximation that simplifies the eikonal equation.
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An Improve Convolutional Auto-Encode Denoising Method
More LessSummaryWe evaluated an improve Convolutional Auto-Encode method for seismic data denoising. The method learn extremely complex functions to effectively attenuate noise by learning and extracting features from a large amount of training data set based on statistical techniques. However, the large quantity of training point pairs may increase the burden of memory and computation during the training. To solve the problem, we develop entropy sampling to select the effective training point pairs and reduce the training set based on the texture complexity. That is, complex texture regions represent the dominant characterization of the seismic data, and these regions are sampled with higher probability as training data set. Numerical illustrations on 2D seismic data show that the proposed method reduces the training data pairs as much as possible to improve the efficiency of training, while ensuring accurate denoising results.
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A Quantitative Estimation Method of Cement Clay in Clayey Sandstone and Its Rock Physics Application
SummaryWhen building the rock physics model for clayey sandstones, it is very important to know the contact type and content of cement clay in clayey sandstone for correctly understanding the influence of the cementation on acoustic velocity of clayey sandstone and how to reasonably establish rock physical model. At present, there is no laboratory method to directly quantitatively estimate the content of the cement clay, which leads to large errors in predicting acoustic velocities when using the cemented sands model for cemented sands formation because of the over-estimated of the cement clay. In this paper, a method for distinguishing cemented clay is proposed by observing the contact relationship and relative distribution between clay and particles in thin sections. The cement clay is used as the input parameter of the constant cement model. The comparison shows the velocities error predicted in our method is 20% lower than the original model, and the predicted results are significantly improved. The method proposed in this paper is a suitable rock physics model for weak cemented formation. It can predict acoustic velocity to identify favorable reservoirs and quantitatively evaluate reservoir parameters by combining seismic and logging data.
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Q-Compensated Least-Squares Reverse Time Migration of Different-Order Multiples
More LessSummaryMultiples have longer propagation paths and smaller reflection angles than primaries, so they cover larger illumination area. Therefore, multiples can be used to image shadow zones of primaries. Least-squares reverse time migration of multiples can produce high quality images with fewer artefacts, high resolution and balanced amplitudes. However, viscoelasticity exists widely in the earth, especially in the deep-sea environment, and the effect of attenuation on multiples is more serious than primaries because multiples have longer propagation paths. To compensate for Q attenuation of multiples, Q-compensated least-squares reverse time migration of different-order multiples is proposed by deriving Q-compensated born modeling operators, Q-compensated adjoint operators and Q-attenuated demigration operators for different-order multiples. Based on inversion theory, this method compensates for Q attenuation along all the propagation paths of multiples. A stabilization operator is introduced to suppress exponential high frequency noise. Example on a modified attenuating Sigsbee2B model suggests that the proposed method can produce better imaging result than Q-compensated least-squares reverse time migration of primaries and noncompensated least-squares reverse time migration of multiples.
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Pure P- and S-Wave Equations in Anisotropic Media
Authors A. Stovas, T. Alkhalifah and U. Bin WaheedSummaryPure mode wave propagation is important in applications ranging from imaging to avoiding parameter tradeoff in waveform inversion. We propose new artifact-free approximations for pure P- and S-waves in a transversely isotropic medium with vertical symmetry axis. Our approximations are very accurate compared to other known approximations as it is not based on weak anisotropy assumptions. As a result, the S-wave approximation can reproduce the group velocity triplications in strongly anisotropic media.
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Suppressing Seismic Record Linear Noise on the Common Offset Gathers Using Mathematical Morphology Filters
More LessSummaryThe attenuation of linear coherent noise is a persistent problem in seismic processing and imaging. Traditional methods utilize the differences in frequency, wavenumber or amplitude between useful signals and noise to separate them. However, in some cases, the differences are too small to be distinguished, and the traditional method are limited or even invalid. So we introduce mathematical morphological filter to attenuate the linear coherent noise utilize the differences in the shape of seismic waves. In the seismic exploration, we can see that the same linear coherent noises exist in some different common shot gathers. After investigation, we find that the trajectories of linear coherent noises in the common offset gather are horizontal continuous ones. So we implement the MMF attenuation the linear noises in the common offset gathers by using the horizontal consistency. And apply the proposed method on field seismic to show the excellent performance.
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Correcting Density/Sonic Logs for Total Organic Carbon to Reduce Uncertainty in Pore Pressure Prediction
More LessSummaryPore pressure prediction in shales undergoing compaction, including mechanical and chemical diagenesis, is customarily related to the mechanism referred to disequilibrium compaction. However, even when this mechanism is established and the normal compaction trend in sonic velocity, as a proxy for shale porosity, is well constrained, the pore pressure prediction may be in error because of the lithological variation in shale composition. Presence of high levels of organic matter in shales that are immature for hydrocarbon generation is an example, causing marked overprediction of pore pressure unless properly accounted for. All published datasets involving TOC and wireline data record a similar relationship between TOC and the bulk density and P-wave velocity log response, in the sense that the measured wireline data shows a decrease (which implies an increase in porosity) as the TOC content increases. In this paper it has been shown that a rock physics model that links TOC and bulk density can be utilised to correct the measured bulk density in immature shales, and, when limited to immature shale, the correction can be extended to velocity data using simple industry-standard models.
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Fault Reactivation Controlled by Elastic Stress Transfer during Hydraulic Fracturing at Preston New Road, UK
Authors T. Kettlety, J. Verdon, M. Werner and M. KendallSummaryWe investigate the physical mechanisms that produced felt seismicity during hydraulic stimulation of the Preston New Road PNR-1z well in Lancashire, England in October – December 2018. While pore pressure increases are typically assumed to be the principal cause of induced seismicity, other factors such as poroelastic stress transfer and aseismic slip have also been proposed as alternative mechanisms. At PNR-1z, a downhole microseismic monitoring array detected and located over 38,000 events during the stimulation, which revealed the interaction between the hydraulic fractures and a pre-existing fault. Here we probe this interaction in more detail, focussing on the role played by elastic stress transfer produced by the tensile opening of hydraulic fractures. We generate stochastic models to simulate the impact of tensile fracture opening on the surrounding stress field, and find that the observed microseismic event locations occur predominantly in regions where these effects moved the stress conditions towards the failure envelope. We therefore conclude that elastic stress transfer from tensile opening of hydraulic fractures played an important role in controlling fault reactivation at this site.
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A Dynamic Model for Non-Newtonian Drilling Fluid’s Filtration in Casing Drilling Technology
Authors M. Vasheghani Farahani, M. Salehian and S. JamshidiSummaryCasing Drilling is a recent technology for simultaneously drilling and casing a well. Using casing instead of conventional drill pipe results in a relatively small annular space between the conduit and wellbore, where the shear rate caused by drill pipe rotation can significantly affect the mud cake thickness. Previous studies have developed dynamic models to estimate mud cake characteristics in conventional drilling operations, however, the detailed information regarding the impact of drill pipe rotation on mud cake and formation damage has not been deeply addressed yet. This study presents a dynamic model for mud filtration in an isothermal radial system, while considering the impact of shear rate on mud cake thickness and filtration radius. Here, we use the Power-Law as the rheological model of the non-Newtonian drilling fluid. Results show the necessity of considering drill pipe rotation effect in dynamic flow calculations, highlighting the advantage of here-developed model for accurate estimation of mud cake characteristics in casing drilling operations.
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Time-Domain CSEM Modelling Using Frequency- and Laplace-Domain Computations
Authors D. Werthmüller and E.C. SlobSummaryModelling time-domain electromagnetic data with a frequency-domain code requires the computation of many frequencies for the Fourier transform. This can make it computationally very expensive when compared with time-domain codes. However, it has been shown that frequency-domain codes can be competitive if frequency-dependent modelling grids and clever frequency selection are used. We improve existing schemes by focusing on (a) minimizing the dimension of the required grid and (b) minimizing the required frequencies with logarithmically-spaced Fourier transforms and interpolation. These two changes result in a significant speed-up over previous results. We also tried to further speed-up the computation by using the real-valued Laplace domain instead of the complex-valued frequency domain. Computation in the Laplace domain results in a speed-up of roughly 30% over computation in the frequency domain. Although there is no analytical transformation from the Laplace to the time domain we were able to derive a digital linear filter for it. While this filter works fine for exact analytical responses it turned out that it is very susceptible to the smallest error. This makes it unfortunately unsuitable for iterative 3D solvers which approximate the solution to a certain tolerance.
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Integrated Geophysical Study for Landfill Mining: A Case Study in Denmark
Authors A. Sandrin and J. KeidingSummaryIn the last years the discipline of Urban Mining has been established, and the existing landfills may be now considered as a source of valuable commodities. For the estimation of the presence and amount of recyclable materials, a thorough exploration approach is strongly recommended. Non-invasive investigation methods are obviously preferred, due to the potentially high environmental impact of invasive methods in case of accidents. In this paper it is presented a case history from a landfill in Denmark.
A set of geophysical surveys was performed to determine the presence of metals within the waste, and possibly define their location and depth. The integration of magnetic, geoelectric, and seismic data seem to be able to provide a reliable assessment of the presence of magnetic metals at around 8 m depth in the westernmost part of the landfill. More detailed exploration methods and modelling techniques will be required for a quantitative evaluation of the valuable volumes in place.
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Mechanism of Overpressure Generation in the Paleocene Shahejie Formation in in the Linnan Sag, Eastern China
More LessSummaryIn this paper, the log response–vertical effective stress and acoustic velocity-density crossplots are used to identify the characteristics and generation mechanisms of the overpressure in the Linnan Sag. The analyses of the acoustic velocity/density–vertical effective stress and acoustic velocity-density crossplots demonstrate that the overpressured points consistent with the loading curve. So, the disequilibrium compaction of the thick Paleocene mudstones is the fundamental mechanism resulting in overpressures. Hydrocarbon generation and vertical transfer may be the main unloading mechanisms, that correspond to the overpressure points that deviate from the loading curves. Since organic matter cracking may occur in formations at depths deeper than 3800m, the contribution of hydrocarbon generation to overpressuring should be limited. The transfer of overpressure via opening faults is therefore considered as the main cause of higher overpressure in local sandstones. The results of this analysis provide an indication of the magnitude, mechanism and distribution of the overpressure. This understanding will help to guide further exploration activities in the Linnan Sag and similar geological basins.
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Azimuthal Seismic Difference Inversion for Tilted Fracture Weaknesses
Authors H. Chen and K. InnanenSummaryTilted transverse isotropy (TTI) provides a useful model for analyzing how tilted fractures affect seismic wave propagation in subsurface layers. To determine the TTI properties of a medium, we propose an approach of employing azimuthal differencing of seismic amplitude data to estimate tilted fracture weaknesses. We first derive a linearized P-to-P reflection coefficient expression in terms of tilted fracture weaknesses, and then we formulate a Bayesian inversion approach in which amplitude differences between seismic data along two azimuths are used to determine tilted fracture weaknesses. Tests with simulated data confirm that the unknown parameter vector involving tilted fracture weaknesses is stably estimated from seismic data containing a moderate degree of additive Gaussian noise. Applying the inversion approach to real data, we obtain interpretable tilted fracture weaknesses, which are consistent with expected reservoir geology.
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Coalbed Mathane Enrichment Rule and Sweet Spot Optimization-Case Study from Australia North Bowen Basin
By M. LiSummaryThe Bowen Basin in Australia is a typical post-arc foreland coal-bearing basin. There are high Coalbed Mathane resource potential in the North Bowen Basin. The study block in this paper is mainly located in the North Bowen Basin and the Moranbah field was the first developed Coalbed methane field in this block. Combined with the structural characteristics of the North Bowen Basin, the characteristics of coal seam development, gas bearing characteristics and permeability of coal seams. There are following main controlling factors of Coalbed methane in Moranbah coal group, “Coal distributed by sedimentary factor, Coalbed methane accumulated by hydrological factor, Coalbed methane distributed by structural factor and Coalbed Methane permeability is controlled by stress factor”
On the basis of the law of coalbed methane enrichment rule, the optimization evaluation criteria are summarized. The Sweet Spot, the favourable area and the unfavourable area of the Bowen block are determined according to resources basics, enrichment factors and production factors. It is suggested that Sweet Spot should apply for development permit and begin to the trial production, the favorable area should apply for potential commercial area and block temporal preservation and waiting for future development, and the unfavorable area should apply for relinquishment.
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VSP Study Using DAS at the Medipolis Geothermal Well and Implication of a Deep High-Vp/Vs Zone
Authors J. Kasahara, Y. Hasada, H. Kuzume, H. Mikada and Y. FujiseSummaryFollowing our first seismic study at the Medipolis geothermal field in southwestern Japan in 2018, we conducted a second seismic study at the same geothermal field in 2019. We installed an optical-fiber system for distributed temperature sensor (DTS) and distributed acoustic sensor (DAS) measurements. We deployed the optical-fiber system at a 1,545-m depth in the IK-4 borehole. The temperature was measured to be 272.8 °C at a 920-m depth and 152.8 °C at a 1,530-m depth. We operated a MiniVib seismic source at five locations and performed a frequency sweep of 10–75 Hz 480 times each day, for seven days. We cross-correlated the seismic records and the source signature and stacked the correlated data to enhance the S/N. Stacking for 480 or 960 times considerably improved the arrival waveforms. Based on an analysis of DAS data, we constructed the 2D seismic profile. We estimated three major hydrothermal layers, at depths of 800–1,000 m, 1,300–1,600 m, and 3,600 m. The zone around 3,600 m suggests a high Vp/Vs value and the possible presence of a fluid layer.
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Experimental Study on the Effect of Supercritical CO2 on Shaly Caprocks
More LessSummaryPetrophysical properties such as porosity and pore size distribution are critical parameters in seal integrity of the caprock. The effect of interactions between CO2, brine, and minerals constituting the caprock, have a significant influence on the effectiveness of the caprock sealing properties. Alteration of caprock integrity leads to environmental problems and bringing into question the effectiveness of the program altogether. In this study, shale samples were exposed to supercritical CO2 (scCO2) at in-situ pressure, temperature, and salinity condition, representative of a CO2 storage operation in Southwest Hub, Western Australia. Petrophysical properties of the samples are analysed with several methods to track the changes after exposure of samples to CO2. With this approach, we show that in the context of tight samples, the alteration of caprock minerals could result in either porosity enhancement or diminishment. Pore size distribution curves form nuclear magnetic resonance (NMR), low-pressure nitrogen adsorption (LPNA), and mercury injection capillary pressure (MICP) tests indicate an increase in pore volume, except for relatively tighter, clay-rich samples.
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Converted Wave Traveltime Approximation in Elastic Orthorhombic Media
More LessSummaryIn order to approximate the traveltime in an elastic orthorhombic (ORT) medium for converted waves, we define an explicit rational-form approximation for the traveltime of the converted PS1, PS2 and S1S2 waves. For the simplification purpose, The Taylor-series approximation is applied in the corresponding vertical slowness for three pure-wave modes. By using the effective model parameters for PS1, PS2 and S1S2 waves, the coefficients in the converted-wave traveltime approximation can be represented by the anisotropy parameters defined in the elastic ORT model. The accuracy in the converted-wave traveltime for three ORT models is illustrated in numerical examples. One can see from the results that for converted PS1 and PS2 waves, the proposed rational-form approximation is very accurate regardless of the tested ORT model. For a converted S1S2 wave, due to the existence of cusps, triplications, and shear singularities, the error is relatively larger compared with PS waves.
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Traveltime and Relative Geometrical Spreading Approximation in Elastic Orthorhombic Medium
More LessSummaryWe define the Rational Form (RF) approximations for P-wave traveltime and relative geometrical spreading in elastic ORT model. To facilitate the coefficients derivation in these approximation forms, the Taylor series (expansion in offsets) in the vertical P-wave slowness measured at zero-offset is applied. The same approximation forms computed in the acoustic ORT model are also derived for the comparison. In the numerical tests, three ORT models with the parameters obtained from the real data are used to test the accuracy of each approximation. The numerical examples yield the results that, apart from the error along the y-axis in the ORT model 2 for the relative geometrical spreading, the RF approximations are all very accurate for all tested models in both traveltime and relative geometrical spreading that can be performed for the practical use.
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On-Axis Triplications in Elastic Orthorhombic Media
More LessSummaryWe derive the second-order coefficients (principal curvature) of the slowness surface for two S waves in the vicinity of three symmetry axes and define the elliptic form function to examine the existence of the on-axis triplication in ORT model. The existence of the on-axis triplication is found by the sign of the defined curvature coefficients. An ORT model is defined in the numerical examples to analyze the behavior of the on-axis triplication. The plots of the group velocity surface in the vicinity of three symmetry axes are shown for the ORT model where different shapes: convex or the saddle-shaped (concave along one direction and convex along with another) indicates the existence of the on-axis triplication.
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Game-Changing AI for Faster and Better Well Trajectory Planning Decisions (An Example Using the Volve Dataset)
Authors N. Dolle, T. Savels, G.C.A.M. Reijnen-Mooij, J.J. Corcutt, O.R. Hansen and E. LandreSummaryWell trajectory planning is a high-stake and complex multi-disciplinary work activity for Oil & Gas operators. The work involves experts from geoscience, reservoir engineering, drilling, completions and facilities. Each are using specialist software to evaluate and define reservoir targets, subsurface hazards and engineering constraints. “Likes” and “dislikes” of trajectory options are expressed in different terms by the various disciplines. This often leads to an iterative and time-consuming process, influenced by human bias. Time quickly becomes a limiting factor, with a business risk of unrealized value due to incomplete understanding of the full option space and associated uncertainties, risks and rewards.
To mitigate the above challenges, we have developed a collaborative game-based approach to well trajectory planning supported by Artificial Intelligence (AI). This approach has been tested using Equinor’s open source Volve dataset, which demonstrates the potential to significantly reduce cycle time and improve decision quality.
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Multidimensional Factorial Kriging for Prestack Filtering
Authors T. Demongin and C. MagneronSummaryThe presence of stationary and non-stationary noise in prestack seismic data, despite reprocessing improvements, can be tackled by an innovative Factorial Kriging technique. Indeed, the data can be considered in a 4D space, counting the offset value. A multidimensional filter, using a 4D variogram model, is then resolved with the same system as in the case of usual 3D Factorial Kriging.
A NMO corrected raw migration gathers case study is presented, with results and interpretation. It appears in the end that noise observed on gathers and offset planes is removed and the data shows an improved signal to noise ratio.
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Working around the Corner Problem in Numerically Exact Non-Reflecting Boundary Conditions for the Wave Equation
By W. MulderSummaryRecently introduced non-reflecting boundary conditions are numerically exact: the solution on a given domain is the same as a subset of one on an enlarged domain where boundary reflections do not have time to reach the original domain. In 1D with second- or higher-order finite differences, a recurrence relation based on translation invariance provides the boundary conditions. In 2D or 3D, a recurrence relation was only found for a non-reflecting boundary on one or two opposing sides of the domain and zero Dirichlet or Neumann boundaries elsewhere. Otherwise, corners cause translation invariance to be lost.
The proposed workaround restores translation invariance with classic, approximately non-reflecting boundary conditions on the other sides. As a proof of principle, the method is applied to the 2-D constant-density acoustic wave equation, discretized on a rectangular domain with a second-order finite-difference scheme, first-order Enquist-Majda boundary conditions as approximate ones, and numerically exact boundary conditions in the horizontal direction. The method is computationally costly but has the advantage that it can be reused on a sequence of problems as long as the time step and the sound speed values next to the boundary are kept fixed.
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Gramian Constraints in Electromagnetic Multi-Physics Joint Inversion
More LessSummaryJoint inversion of multi-physics is used to minimize the non-uniqueness associated with under-determined geophysical problem by some constraints. The Gramian stabilizing constraint has been used to enforce the linear correlation between the resistivity models from the frequency and time-domain airborne electromagnetic (AEM) data. The Gramian is the dot product of the two resistivity models which constrains the nonlinear least square optimization towards more reliable interpretation even in the presence of noise. Both synthetic and field data demonstrations give satisfactory results.
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Analysis of Thin Sand Recognition Using Supervised Multiattribute Classification Based on ANNs
More LessSummaryThe objectives of this work are to identify heterogeneous thin sands via machine learning (artificial neural network) and evaluate the impact of tuning thickness on the recognition. The thin sands within the study interval mainly developed in a complex fluvial to shallow marine environment. Multiattribute classification using supervised Artificial Neural Networks (ANNs) is employed to predict the distribution of these thin sands within six subintervals and the role of tuning thickness in the prediction is evaluated quantitatively.
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The Performance of Viscoelastic Surfactant-Polymer Flood in Heavy-Oil Carbonate Reservoir — Simulation Study
Authors A. Zaitoun, M. Al-Foudari, K. Zeidani, S. Al-Otaibi, A. Al-Ghadhouri, G. Omonte Rossi, J. Bouillot and A. ZaitounSummaryThis paper describes the simulations performed to evaluate different scenarios of water flood, polymer flood and Viscoelastic Surfactant (VES) combined with polymer blend in a Middle Eastern carbonate reservoir. Compared to classical Alkaline-Surfactant-Polymer (ASP) EOR technology, VES-Polymer does not require heavy water processing and is thus more robust and easier to deploy on the field. The simulation study used coreflood data set obtained by a laboratory study presented in another paper and aimed at optimizing a field pilot.
The simulation was conducted with a pattern of three parallel horizontal wells; one central injector and two lateral producers. A well length of 2000 meters and spacing of 100 meters was found to be the best configuration for the pilot. For waterflood, the unfavorable mobility ratio induced early water channeling. Due to more favorable mobility ratio, polymer flood shows better performances in terms of incremental oil production and VES-Polymer flood further increases the oil production compared to polymer flood due to combination of IFT reduction and increase in sweep efficiency.
Both polymer flood and VES-Polymer flood can thus be considered as valuable EOR options in this type of reservoir conditions which have not been considered so far
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Structural and Depositional Features Controlling Permeability on Carbonate Platforms
Authors R. Loza Espejel and T.M. AlvesSummaryNaturally fractured reservoirs present a challenge when determining the permeability associated with different types and sizes of fractures. Permeability in these reservoirs depends on the heterogeneity and connectivity of open fractures; although depositional and diagenetic features also play an important role. In this study, a multi-scale analysis of the Cariatiz Fringing Reef Unit in SE Spain is completed based on outcrop and LiDAR data. Seven different features were found to influence the permeability of the Cariatiz Fringing Reef Unit. Structural features comprise: (i) joints, (ii) veins, (iii) vertical fractures, (iv) fracture swarms, and (v) karsts. Two types of depositional features were also recognised at outcrop:(vi) vertical Porites and (vii) pseudo-bedding surfaces. All contribute to increased permeability, apart from calcite-filled veins that create barriers to fluid flow. The results of this study highlight the complexity of carbonate systems and the need to collect data at different scales of analysis to decrease uncertainties in reservoir models. The approach in this work is valid in hydrocarbon exploration and production, geothermal reservoir characterisation, environmental studies and carbon sequestration projects.
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Deep-Marine Hyperpycnal Sandstones and Implications for Exceptional Reservoir Quality Preservation
Authors J. Cater, T. Gould and B. UrsinusSummaryDeep marine hyperpycnal sandstones form prolific hydrocarbon reservoirs but remain poorly understood despite over 40 years of research. Predicting their geometry, composition and reservoir quality requires a thorough knowledge of the processes that formed them and the effects of diagenesis in the presence of brackish depositional pore waters. Dissolution of unstable grains (e.g. feldspars and volcanic material) and replacement by kaolinite and chlorite/smectite occurs more readily in the presence of brackish, acidic pore fluids. This is enhanced locally as compaction drives fluids through the aquifer. Pore lining chlorite cements can help to prevent chemical compaction of quartz grains and impede later quartz overgrowths, helping to preserve reservoir quality at depth. Commonly in hyperpycnal deposits, remnant pore fluids are of low salinity, resulting in anomalous low salinity DST results (e.g. Agat, NOCS). The salinity of the pore fluids soon after deposition can be quantified by measuring the isotopic composition of early carbonate cements, which may form strata bound or nodular baffles to flow within the aquifer. The influence and mobility of low salinity pore fluids during the early diagenesis of deep marine hyperpycnal deposits is a key subject for future research.
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Lithology Identification Based on Hidden Markov Model and Random Forest
More LessSummaryBy combining the hidden Markov model (HMM) and random forest (RF), a new approach is proposed for lithology identification. To extract more useful information from elastic parameters, the HMM is used to provide a new hidden feature. The hidden feature reveals the inner relationship of elastic parameters and this is important for machine learning. With the new hidden feature and elastic parameters, RF is adopted for lithology prediction. To guarantee the quality of the hidden feature, it is updated in a loop iteration. Both synthetic data and field data tests demonstrate that the proposed approach can improve prediction results.
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Use of Elastic Forward Modeling to Remove Complex Coherent Noises
Authors J. Tang, C. Peng, M. O’Briain and C. ShihSummaryIn the deep-water Campeche Bay area of the southern Gulf of Mexico, there are many complex shallow salt bodies and carbonate rafts that generate a significant amount of coherent noise energies, collectively for all non-primary reflection energies, as a result of the high impedance contrast between these bodies and the surrounding sediments. These noise energies include surface-related salt-diffracted multiples, interbed/internal multiples, bounces between salt bodies, and other types of prismatic waves as well as converted shear waves. These coherent noises cause difficulties in interpreting base of salt and subsalt seismic events. Identifying and removing them is crucial for optimal seismic imaging of subsalt targets.
We propose a method to model these noises using a geological imaging model and elastic finite-difference forward modeling. The method requires that the shallow part of the geological imaging model be accurate. We first compute elastic synthetic data using the model. Then, we migrate the synthetic data to generate a noise model in the image domain and use this noise model to pattern-match with another image volume migrated using field data. In this way, we can identify noises in the field data and remove them adaptively to obtain a cleaner image of the recorded reflectivity.
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Performance Evaluation of Machine Learning Algorithms in Predicting Dew Point Pressure of Gas Condensate Reservoirs
Authors P. Ikpeka, J. Ugwu, P. Russell and G. PillaiSummaryAccurate knowledge of the dew point pressure for a gas condensate reservoir is necessary for the design of a field development plan and timing for optimization of mitigation operations for resources management. This study explores the use of machine learning models in predicting the dew point pressure of gas condensate reservoirs. 535 experimental dew point pressure data-points with max temperature and pressure of 304F and 10500psi were used for this analysis. First, multiple linear regression (MLR) was used as a benchmark for comparing the performance of the machine learning models. Neural Networks (NN) [optimized for the number of neurons and hidden layers], Support Vector Machine (SVM) [using radial basis function kernel] and Decision Tree [Gradient boost Method (GBM) and XG Boost (XGB)] algorithms were then used in predicting the dew point pressure using gas composition, specific gravity, the molecular weight of the heavier component and compressibility factor as input parameters. The performances of these algorithms were analyzed using root mean square error (RMSE), absolute average relative deviation percentage (AARD %) and coefficient of determination (R2). This work concludes that for large data sets neural network is preferred but for smaller data sizes, SVM shows better performance
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Enhancing Massive Land 3D Seismic Data Using Nonlinear Beamforming: Performance, Quality and Practical Trade-Offs
Authors I. Silvestrov, A. Bakulin, D. Nekluydov, K. Gadylshin and M. ProtasovSummaryModern land seismic data are typically acquired using high spatial trace density but single sensors or small source and receiver arrays. These datasets are challenging to process due to their massive size and rather low signal-to-noise ratio caused by scattered near surface noise. Prestack data enhancement becomes a critical step in processing flow. Nonlinear beamforming was proven very powerful for 3D land data. It requires computationally costly estimations of local coherency on dense spatial/temporal grids in 3D prestack data cubes and poses inevitable trade-off between performance of the algorithm and quality of the obtained results. In this work, we study different optimization schemes and discuss practical details required for applications of the algorithm to modern 3D land datasets with hundreds of terabytes of data.
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Improved Ooil Recovery by Low Salinity Water Injection Simulation
By J. TrivediSummaryPrimary and secondary oil recovery techniques together can produce less than half of the original oil in place due to some restricting phenomena such as rock heterogeneity, capillary, and mobility ratio problems during these first two stages in oil reservoirs.( Kamranfar and Jamialahmadi 2014 ; Lei et al. 2016 ). The overall objective of implementation of any chemical EOR method including alkaline, surfactant, and polymer flooding is to decrease the residual oil saturation left within reservoir rock porous media after primary and secondary productions. Recently, LSWI (low salinity water injection) is one of the emerging IOR techniques for wettability alteration in both sandstone and carbonate reservoirs.
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Deep Learning for Anisotropy Parameters Estimation in Oil/Gas Fractured Reservoirs
Authors G. Sabinin, T. Chichinina and V. TulchinskySummaryWe study the applicability of Deep Learning in solving the problem of estimating the fractured medium parameters, represented as anisotropy parameters of a transversely isotropic model (HTI), using synthetic seismic data. Normal and tangential weaknesses of fractures ∆_N and ∆_T, the Thomsen anisotropy parameters ε, δ, γ, the crack density and the aspect ratio (crack opening) are considered. We develop a neural network model for solving this problem. Trained on synthetic seismograms, it provides quite accurate results. The effectiveness of Deep Learning for the inverse problem is demonstrated. The prospects for the development of this method for more complex rock-physics models are outlined.
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Prestack Data Enhancement with Phase Substitution and Phase Corrections Guided by Local Multidimensional Stacking
Authors A. Bakulin, D. Neklyudov and I. SilvestrovSummaryWe revisit enhancement with local stacking in the context of seismic data corrupted by near surface scattering. We discover that phase spectra derived from local stacking contains critical information that could be used as direct estimate of signal phase (phase substitution method) or as a guide (phase corrections method) to correct frequency-dependent distortions obstructing prestack data. Combining corrected phase with original amplitude spectrum, we arrive at much better estimate of enhanced data compared to conventional multi-dimensional local stacking. Specifically, we eliminate loss of higher frequencies and preserve original amplitudes, while making originally invisible reflections to become discernable and coherent for further processing. While we only present example of two possible methods, this discovery paves the way to plethora of new approaches finally enabling removing corrupting effects of complex scattering near surface beyond conventional surface-consistent processing.
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(When) Do Earthquakes Respect Traffic Lights?
Authors S. Baisch, P. Carstens, R. Vörös and K. WittmannSummaryTraffic light systems (TLSs) for limiting the strength of induced seismicity are used in different energy technologies. We use physics-based numerical models for investigating under which circumstances TLSs may not provide a robust mitigation measure. For seismicity induced by fluid injection, TLS efficiency can be limited by trailing effects caused by post-injection pressure diffusion and stress concentrations at the periphery of previous seismic activity. Seismicity caused by gas production exhibits a ‘characteristic earthquake’ pattern where earthquakes with similar (maximum) magnitude occur in the course of reservoir depletion. The characteristic earthquakes reflect repeated slip of the same reservoir fault patches. The maximum earthquake magnitude of a sequence can occur without precursors. Although trailing effects do not occur in an idealized reservoir with infinite conductivity, the lack of precursory seismicity limits the robustness of a TLS.
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Moving Toward Direct DNN-Based Enhancement of 3D Pre-Stack Seismic Data
Authors K. Gadylshin, A. Bakulin and I. SilvestrovSummaryPre-stack data enhancement with multidimensional stacking is indispensable part of modern data processing that very compute-intensive since multiple wavefront attributes need to be estimated on dense spatial/temporal grid. At the core of this demand are conventional local or global optimization techniques. We propose two alternative approaches based of artificial intelligence that can greatly reduce computational effort of estimation stage. First approach performs traditional computations on sparser grid and inpaints to dense grid using deep neural network (DNN) with partial convolution layers. Second approach is direct DNN-based attributes estimation from the pre-stack seismic data itself. Both methods incorporate multiparameter attributes by encoding them into RGB-images. On synthetic and real 3D data examples, we demonstrate, that application of these methods for seismic data enhancement using nonlinear beamforming can greatly speed up the computational time while maintaining similar quality of output data.
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Blended Acquisition with Temporally Signatured/Modulated and Spatially Dispersed Source Array: Productivity Enhancement in a Pilot Survey
Authors T. Ishiyama and T. WeiSummaryRecently, we established a blended-acquisition method: temporally signatured and/or modulated and spatially dispersed source array, namely S-/M-DSA, that jointly uses various signaturing and/or modulation in the time dimension and dispersed source array in the space dimension. We have acquired the first pilot survey with S-/M-DSA onshore Abu Dhabi. In this paper, we introduce this pilot survey and the resulting acquisition productivity enhancement in the time dimension. Furthermore, we discuss how this method could enhance the acquisition productivity in the space dimension as well. These show that S-/M-DSA significantly enhances the acquisition productivity compared to conventional blending methods.
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Mixed Phase Seismic Wavelet Estimation using the Bispectrum
By M. BekaraSummaryThe ability to estimate a mixed phase wavelet is a useful tool for processing and quality control in seismic imaging. The wavelet is estimated using higher order statistics of the data. In practice, these methods tend to show some instability issues when the wavelet length is increased. To improve the stability of the solution, this abstract proposes a new formulation of the wavelet estimation problem that constrains the solution to be a finite duration, phase-only compensation applied to a known base wavelet. The proposed solution works in the frequency domain and consists of three steps. First, the bispectrum of the data is deconvolved using the bispectrum of the base wavelet to increase its bandwidth. This helps to improve the sensitivity of third order statistics to phase information. Then, a phase-only wavelet is estimated from the deconvolved bispectrum using an iterative least-squares approach without phase unwrapping. Finally, the estimated phase-only wavelet is conditioned using a projection onto convex sets type algorithm to enforce the constraint of the finite time duration giving the user a control on the amount of phase deviation from the base wavelet. Test examples on synthetic and real data both show reliable results with robustness to noise contamination.
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Least-Squares Kirchhoff Psdm with a Local Based Inversion Approach and Compensation for Limitations in Modeling.
Authors Ø. Korsmo, S. Crawley, C. Zhou, S. Lee, E. Klochikhina and N. CheminguiSummaryReliable seismic amplitudes are crucial for the estimation of rock properties. In conventional depth imaging, amplitudes and resolution will be influence by propagation effects in the imaging model. These limitations origin from the formulation of the migration operator, implemented as the adjoint rather than the inverse of modeling. Least-squares migration (LSM) tries to eliminate these effects and resolve the real reflectivity model.
In this study, we make use of a newly developed local calibrated image-domain Kirchhoff least-squares migration to deconvolve the system response from the depth migrated gathers. We demonstrate how the inversion de-blurs the image and adjusts the prestack amplitude response, following better the expected response from well synthetic. The method is demonstrated on a North Sea dataset from the Viking Graben area, covering the Verdandi/Lille Prinsen discovery.
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Seismicity-Permeability Coupling in the Breaching and Sealing of Reservoirs and Caprocks
Authors D. Elsworth, Y. Fang, K. Im, C. Wang, T. Ishibashi, Y. Jia, E.C. Yildirim and F. ZhangSummaryThe presence of pre-existing faults and fractures in the upper crust contribute to induced seismicity as a result of fluid injection, in hydraulic fracturing, deep storage of CO2, and stimulation of EGS reservoirs. In all of these, either maintaining the low permeability and integrity of caprocks or in controlling the growth of permeability in initially very-low-permeability shales and geothermal reservoirs are key desires. We explore styles of permeability evolution using both experimental and computational methods to explore how fracture permeability changes in response to fracture/fault reactivation and investigate the roles of (1) mineralogy and (2) fracture roughness in conditioning response; together with (3) intrinsic controls of healing on the earthquake cycle and permeability evolution.
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A Perfectly Matched Layer Technique for the Lattice Spring Model
More LessSummaryThe lattice spring model (LSM) combined with the velocity Verlet algorithm is a newly developed scheme for modeling elastic wave propagation in solid media. Unlike conventional wave equation based schemes, LSM is established on the basis of micro-mechanics of the subsurface media, which enjoys better dynamic characteristics of elastic systems. But LSM is still suffering the boundary reflections and little work has been reported on this topic. The focus of the present study was to develop a special form of absorbing boundary condition based on the perfectly matched layer (PML) concept for LSM. The PML formulation is tested using a homogeneous model and the Marmousi model. The perfectly matched layer concept appears to be very well suited for LSM.
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Design of Non-Replicated Acquisition Geometries for Time-Lapse Measurements
Authors G. Blacquiere and G. BlacquiereSummaryTime-lapse, or 4D seismic is capable of satisfying the continuously increasing demand for high-quality subsurface images to reveal both static and dynamic elements during the field development. However, in practice, challenges of pursuing this strategy lie in different perspectives related to budgetary, operational and regulatory constraints. Seismic surveys, performed in a compressed manner in time and/or space, can provide high-quality seismic datasets in a cost-effective and productive manner. The processing of data acquired in this way usually requires decompression, e.g., deblending and data reconstruction. The decompression performance is of fundamental importance in determining the success of compressed measurements. Our decompression approach deals jointly with deblending and data reconstruction via a sparse inversion, coupled with constraints on causality and coherency. Additionally, we carry out the inversion simultaneously for all available vintages, sharing static information between them while extracting the dynamic changes. We use this inversion as the kernel of a survey-design scheme. We use artificial intelligence (convolutional neural network) to speed up the computations. In our experiment, using time-lapse data from the Troll field, the improvement of designing the acquisition geometry combined with the simultaneous inversion of all available vintages was 6 dB.
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Application of Stochastic Method for Geomechanical Parameters under Uncertainty Quantification to Design Mud Window
Authors M.A. Ebrahimi, M.J. Ameri and M. AhmadiSummaryA novel methodology is developed to design a reliable safe mud window based on most updated geometrical uncertainty distribution. The developed approach allows to estimate the uncertainty ranges for geometrical parameters and their dependent parameters such as collapse pressure and fracture pressure. A trustable mud window design based on posterior probability reduces the risks of wellbore stability problems and less kick.
In this research, the Markov chain Monte Carlo simulation used to quantify the geomechanical uncertainties in order to make it more clear and trustable.
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Seismic Quality Factor Estimation with a Simulated Annealing Approach: A Practical Example of the Sichuan Basin
More LessSummaryFluid movement and grain boundary friction are the two main factors responsible for the anelastic attenuation of seismic data. The quality factor Q quantifies the degree of anelastic attenuation and is commonly used in assisting the identification of gas reservoirs. We propose to employ the seismic reflections at near offset as referred seismic signals in the quality factor computation while the seismic reflections at medium and far offsets are regarded as target seismic signals. We then employ simulated annealing to simultaneously obtain the quality factor values of the targeted seismic signals. The proposed method is applied to both synthetic and real seismic data to demonstrate the validity and effectiveness. The application of SiChuan field data demonstrates that the estimated Q values using our method can be used as direct indicator the for gas reservoir.
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Multicomponent 3D-3C Data Acquisition and Processing in the Bandurria Norte Concession, Neuquén Basin, Argentina
More LessSummaryHydraulic well stimulation requires knowledge of rock mechanical parameters to reduce uncertainty attached to development of shale oil prospects. Multicomponent 3D-3C seismic data provide more reliable estimation of rock physical parameters needed for fracture stimulation in low permeability unconventional reservoirs. The design and processing of a special 3D-3C seismic survey in the Bandurria Norte concession is illustrated, whereby the Jurassic/Cretaceous Vaca Muerta Formation interval is the main target.
Seismic characterization of unconventional reservoirs necessitates: 1) high resolution input data with a high trace-to-trace correlation, 2) high signal-to-noise ratio, 3) reliable amplitudes and 4) preserved post-migration azimuthal information. Multicomponent seismics make analysis of seismic anisotropy and shear wave splitting possible. The PP-PS joint inversion scheme generates more accurate elastic properties (e.g. Young’s modulus). For these reasons, a static cable-less acquisition spread of 600 three-component (3C) receivers was laid out during the standard P-wave seismic acquisition in the Bandurria Norte Block. The multicomponent data was successfully processed and interpreted. Estimation of shear wave splitting effects improves the velocities with a positive impact on the PreSTM imaging. Directional dependency of the seismic velocities is thought related to fracture distribution and local stress regime.
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What is the Benefits of Carbonated Water Injection in Heavy Oil Reservoirs: A Case Study
Authors M. Shokriafra, H. Norouzi, B. Rostami and P. AbolhosseiniSummaryAdvantage of CWI over WI and CO2 injection for an Iranian heavy oil reservoir, is studied through core flooding experiments. Five different experiments were conducted in different wettability states using secondary and tertiary injection scenarios. The results showed that CWI is more beneficial than WI and CO2 injection. Higher sweep efficiency, more stable front, CO2 diffusion to oil and subsequent oil viscosity reduction and swelling are the reasons for better CWI performance. Moreover, due to the lower sweep efficiency of WI and low resistance channels created along the flow axis, tertiary CWI is not capable to recover all the bypassed oil, so its recovery is less than secondary CWI. The results of aged experiments indicated that by shifting wettability toward mixed wet, CWI performance decreased in both WI and secondary CWI. In mixed wet wettability several pores which were accessible for injection fluid in clean sand, are not reachable in aged sand anymore which accelerated injection fluid breakthrough and decreased ultimate recovery. Besides, it was observed that the proportion of recovery after breakthrough to the total recovery was increased for SCWI while decreased for WI, this is attributed to the acidic nature of carbonated water and consequent wettability alteration.
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A Multi-Axial Perfectly Matched Layer for Finite-Element Time-Domain Simulation of Elastic Wave Propagation
More LessSummaryWe develop a novel M-PML absorbing boundary condition for the second-order finite-element elastic wavefield simulation. We first derive the M-PML formulation and then incorporate the M-PML into the second-order wave formulation in the time domain with fewer split terms to reduce memory requirement and consequentially improve the computational efficiency. Numerical wavefield simulations are carried out to demonstrate the stability and efficiency of the proposed M-PML. The proposed algorithm can also be extended to 3D anisotropic elastic simulation of wave propagation with reasonable efforts.
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A Novel Nonlinear Joint AVA Inversion Method for Russell Fluid Factor
More LessSummaryFluid factor, as an important characterization parameter for reservoir fluid identification, is mainly estimated by the inversion methods based on the linear approximations of Zoeppritz equations. For complex hydrocarbon reservoirs, the calculation accuracy of the linear approximate formulas is low, which greatly limits the estimation accuracy of the fluid factor. To solve this problem, a nonlinear fluid factor inversion method directly based on the Zoeppritz equations is presented in this abstract. Firstly, based on poroelasticity theory, we performed several substitutions to convert the Zoeppritz equations from the classical form to a new form containing the chosen fluid factor, shear modulus and density (FMR). Then, the objective function was constructed using the new equations in a Bayesian framework. The Cauchy and Gaussian distributions were used for a priori distribution and the likelihood function, respectively. Lastly, the nonlinear objective function was solved by using the Gauss-Newton method. Both synthetic and field data show that the proposed method can stably estimate the fluid factor with high accuracy, and the accuracy is higher than that of the method based on Russell approximate formula.
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Nonlinear AVA Inversion Based on Bayesian Theory for VTI Media
More LessSummaryFor shale reservoirs with VTI anisotropy characteristic, the inversion methods based on linear approximate formulas are commonly used to estimate the elastic parameters and anisotropy parameters. However, the calculation accuracy of linear formulas is low, which limits the estimation accuracy of these parameters. In fact, the linear approximation formulas are made up of isotropic and anisotropic terms. Numerical experiments show that if we use the exact Zoeppritz equations to replace the isotropic term in these formulas, the calculation accuracy of reflection coefficients can be improved. This can reduce the influence of the calculation error introduced by the forward operator on the inversion result. Therefore, in order to improve the estimation accuracy of reservoir parameters, we constructed a Bayesian nonlinear inversion objective function based on the combined equation obtained by substitution. In addition, the differentiable Laplace distribution blockiness constraint term was also added to the Cauchy background prior model to further improve the vertical resolution of inversion results. Synthetic data test shows that the proposed method can not only inverts Thomsen anisotropy parameters stably, but also accurately estimates the vertical P- and S- wave velocities and density, which demonstrates the effectiveness of this method.
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Ambient Noise Reverse Time Migration Based on Velocity Flood for Fault Imaging
More LessSummaryWe propose a novel ambient noise Transmitted Surface Wave Reverse Time Migration (TSW-RTM) method to image interfaces of fault zones where the crystalline basement rocks truncate against the surrounding sediments. The source and receiver wavefields are propagated in the sediment flood velocity and crystalline flood velocity, respectively. The migrated image is then obtained by applying the zero-lag cross-correlation imaging condition to the forward and backward wavefields. The synthetic test demonstrates that the transmitted surface wave can provide sufficient information to form correct images at the fault surface. We then apply the proposed TSW-RTM method to image a major fault of Tanlu fault Zone near Chao Lake in eastern China, using the surface wave retrieved from the ambient noise data. Compared with the conventional ambient noise tomography method, our method provides a better imaging result with much higher resolution and certainty where both the interface position and dipping angle of fault are well consistent with the previous study. This novel ambient noise imaging method enables us to image the fault interfaces without a priori information of the fault position, which is especially useful in the study areas that are less illuminated by seismic surveys or earthquake events.
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Elastic Least-Squares Reverse Time Migration in the Rugged Seabed Structure
More LessSummaryThe marine deep water is rich in oil and gas resources. However, the severe rugged seabed structure brings great difficulties to seismic imaging in the marine environment. To accurately image the target layer under the rugged seabed interface, an elastic least-squares reverse time migration (LSRTM) in the rugged seabed structure is proposed. This method is based on a coupled equation method, which uses the acoustic wave equations in seawater and the elastic wave equations in the underlying elastic medium. The pressure and the stress are transmitted steadily and continuously by using the acoustic-elastic control equation at the seabed interface. To overcome the influence of the rugged seabed interface, the acoustic-elastic model is meshed into non-uniform curvilinear grids, and the corresponding mapping technique is used to transform the model with the rugged seabed interface to a horizontal one in the curvilinear coordinate system through the coordinate transformation. Therefore, in this paper, we overcome the limitations of the traditional finite difference method in imaging the rugged seabed structure environment caused by its regular rectangular grid generation, and proposed the LSRTM method of the acoustic-elastic coupled medium. Finally, the method of this paper was tested by a typical model trial.
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P-Wave Anisotropy Estimation from 3D VSP Data Acquired with Geophones and DAS at Otway Site
Authors S. Popik, R. Pevzner and A. BonaSummaryStage 2C of the Otway Project involves monitoring of a small-scale (15 kt) CO2-injection using an extensive time-lapse active seismic program. The main components of this seismic monitoring program are 4D surface seismic and 4D VSP surveys acquired before, during and after the injection. Data analysis reveals significant seismic anisotropy of the subsurface, which needs to be estimated and taken into account to improve the quality of imaging with both VSP and surface seismic data.
A wide range of offsets obtained during fifth monitoring survey of the project provides a unique opportunity for anisotropy estimation from 3D VSP data. In this study we compare geophone and Distributed Acoustic Sensor (DAS) VSP data and their applicability for anisotropy analysis. Analysis of DAS data gives anisotropy parameters for the entire depth of the well.
We estimate P-wave anisotropy by analyzing direct-wave VSP arrival times. The study demonstrates significant presence of both polar and azimuthal anisotropy. While vertical-plane anellipticity remains almost constant at 0.1 level for the whole depth range, azimuthal anisotropy changes significantly with depth: from negligibly small in the shallow part with significant increase below the 600 m depth, which most probably indicates the change of stress field at this depth.
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A Comparison of Predicted and Actual Reservoir Quality of Geothermal Projects in the Slochteren Formation
Authors L. Borst, N. Buik, W. Van Leeuwen and N. ShawSummaryNow that four geothermal projects have successfully been completed in the Slochteren Formation, the formation has proven as a valid aquifer for geothermal heating purposes. Before drilling a project, the local reservoir parameters need to be determined in order to determine the economic feasibility of a project. However, predicting this is not an easy task: permeabilities are often strongly overestimated, while temperatures and (net) reservoir thicknesses are often underestimated. This has several causes: first, the available resources for geothermal projects are limited. Therefore, geothermal feasibility studies need to be done with limited amount of time using publicly available data, mostly from hydrocarbon wells. Second, these hydrocarbon wells are drilled with a different objective than geothermal wells, which introduces difficulties when translating the datasets into one another. Thirdly, not all planned geothermal project locations have a high density of well data, which can introduce a large uncertainty in interpreted reservoir properties. As a result, comparing data from these indicative studies to the actual results after drilling of the well discloses certain discrepancies. This study helps to understand where these discrepancies come from, and may improve the accuracy of the estimated geothermal doublet performance on basis of hydrocarbon well data.
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Rock Physics Modelling of Gas Dissolved in Water Sandstone, Nakajo Field, Japan
Authors T. Fukano, T. Mizukami, T. Aoyama and Y. MaeharaSummaryNatural gas dissolved in water (GDW) is a common form of hydrocarbon occurrence in Japan, and gas production from the GDW accounts for 17% (approximately 290 mmscf/day) of total natural gas production in the country. Nakajo field is one of the fields which has long production history from the GDW reservoir. However, as GDW sandstone itself has not been well understood in aspect of the petrophysics and rock physics behaviour, it was a new finding for us that gas-effect and gas-effect-like sonic responses were observed in the GDW sandstone. In this paper, we show result of rock physics modelling, fluid substitutions, synthetic seismogram calculations, wedge modelling and AVO modelling for GDW sandstone. The rock physics modelling results revealed presence of isolated gas in GDW reservoir. Besides, water saturation estimated from rock physics modelling was regarded as useful tool to detect GDW reservoir with gas isolation. An application to seismic data is also encouraged according to synthetic seismogram calculations and AVO modelling. These outcomes allow a better evaluation approach of the surrounding area where future exploration and development potential may exist.
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Role of Prolonged Successive Fluid Flow on the Performance of Relative Permeability Modifiers in Gas Reservoirs
Authors F. Alshajalee, M. Seyyedi, M. Verrall, C. Wood and A. SaeediSummaryExcessive water production is becoming common in many petroleum reservoirs. Relative permeability modifiers (RPM) have been used to disproportionately reduce water permeability (DPR) with minimum effect on the gas/oil phases. This manuscript reports the results of an experimental study where we examined the effect of prolonged successive water-gas injection on RPM’s performance in gas/water system. The results show that the volume of water coming in contact with the polymer-treated porous medium has a direct impact on the extent of polymer swelling and thus the water permeability of the medium. It was also shown that over a large volume of gas injection, treated porous medium presents a better permability for gas at later times compared to the early times of injection. The reason could be the dehydration of the polymer layer adsorbed to the pore surfaces of the medium. It was found that successive water-gas injection could lead to stronger performance of polymer towards reducing water permeability, but it comes with the cost of a further reduction in gas relative permeability.
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Seismic Noise Attenuation Based on Higher-Order Directional Total Variation
More LessSummaryNoise attenuation is one of the key problems in seismic data processing. Total variation (TV) has played an important role in seismic data denoising and reconstruction. We develop a high-order directional total variation method for seismic data denoising that considers the structural direction of the seismic data. It involves a parameter to balance higher-order derivatives, thereby reducing the staircasing effect of the bounded variation functional. We test the method on a model where the data are contaminated by different types of noise. The corresponding denoising performance is compared with the TV and conventional directional total variation method from two aspects of signal-to-noise ratio and effective signal leakage degree. The model test and field data application illustrate the advantage of this functional as a regularization term for seismic noise attenuation.
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Squeezed Diapirs of the Timan Pechora Basin: Structure, Evolution and Petroleum Prospectivity
Authors K. Sobornov, I. Korotkov, K. Kudryavtsev and R. AnisimovSummaryReprocessing and integrated interpretation of vintage and newly available data provided new insight into structural framework of thrust belt in the northeastern part of the Timan Pechora basin. It showed that structural evolution of the fold and thrust belt was influenced by the multiphase development of salt diapirs which finally were squeezed during pulses of the orogenic shortening. This was accompanied with expulsion of salt and the development of divergent thrusting. The improved seismic imaging has allowed for more accurate definition of the structure and stratigraphy below thrust sheets including salt sole in frontal zone of the fold and thrust belt. The updated interpretation shows new exiting opportunities for petroleum exploration provided by subsalt traps.
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Stratigraphic Forward Modelling Applied to Reservoir Characterisation of Pre-Salt Carbonate Reservoirs, Santos Basin, Brazil
SummaryThis work proposes the use of stratigraphic forward modelling to test and quantify concepts about the evolution of the carbonate platform of a Pre-Salt field, as well as to use the results as trends for stochastic simulations of facies in geocellular reservoir models. The facies model was performed in three steps: (1) facies interpretation in the wells using rock data (core and sidewall samples) and image logs; (2) forward modelling simulation to control the carbonate reservoir geometry and low-frequency heterogeneities; (3) stochastic simulations of the facies, which aims to generate a high-frequency variability of facies and honour the well data. Subsequently, this final facies model, based on geological knowledge and geostatistic approach, will be the background for the propagation of the petrophysical rock properties (porosity and permeability).
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Characterization and Modeling of the Vug and Fracture Network Affecting a Carbonate Reservoir (Kmz - Mexico)
SummaryThe Cretaceous reservoir of the KMZ field consists of brecciated, carbonate rocks characterized by the presence of a complex system of natural fractures and solution vugs. As this high-permeability system plays a major role on the fluid circulation in the field, it is crucial to build-up a 3D model in order to quantify its dynamic impact. To do this, we applied the methodology for the analysis of fractured reservoir FracaFlowTM developed by the IFPEN/Beicip-Franlab group, integrating BHI data, structural information (3D seismic) and dynamic data.
Both diffuse and fault-related fractures were recognized in the field, whereas vugs largely affect mainly the brecciated layers of the reservoir. The innovation of the present study is the modeling of the vugs, with the software FracaFlowTM, as independent objects overprinting the matrix properties and distributed independently from fractures. This allows to take into account and calibrate separately the permeability of the vugs and fractures.
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Seismic Acoustic Impedance Estimation by Learning From Sparse Wells via Deep Neural Networks
Authors H. Di, X. Chen, H. Maniar and A. AbubakarSummarySeismic acoustic impedance is one of the most important properties closely related to the subsurface geology, and thus robust acoustic impedance estimation from seismic data is an essential process in subsurface mapping and reservoir interpretation. For compensating the limited bandwidth in seismic data, one feasible approach is to integrate 3D seismic volume with 1D wells that are usually sparsely distributed within a seismic survey, and such integration aims at finding the optimal non-linear mapping function between them. Most of the existing mapping methods, particularly these powered by machine learning, are performed in 1D and/or require down-sampling of well logs to the seismic scale, which run of the risk of limiting the estimation valid only around the training wells and fail to provide consistent prediction throughout the entire seismic survey.
We present a semi-supervised learning workflow for estimating the acoustic impedance over a given seismic survey by learning from a small number of sparsely-distributed wells via two deep neural networks. Applications to the synthetic SEAM dataset of a complex salt intrusion demonstrates its capability in reliable seismic and well integration, particularly in the zones of poor seismic signals due to the presence of geologic complexities, such as saltbodies.
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Diffraction Separation and Holistic Migration: High-Resolution Imaging Beyond Nyquist
Authors L. Gelius and V. Stenbekk ThorkildsenSummaryIn case of a broken hologram, an image of the complete object can still be obtained from one of the fragments. The reason is that each diffraction point of the object sends out waves that reach every point on the hologram. As an analogy, we propose to separate diffractions from standard seismic reflection data. The use of a decimated version of such data (violating the Nyquist sample condition) should still contain all necessary information to obtain an image of the finer details of the subsurface employing the concept of holographic migration. The feasibility of the proposed approach is supported by a field data example from the Barents Sea.
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Langevin Dynamics Markov Chain Monte Carlo Solution for Seismic Inversion
Authors M. Izzatullah, T. van Leeuwen and D. PeterSummaryIn this abstract, we review the gradient-based Markov Chain Monte Carlo (MCMC) and demonstrate its applicability in inferring the uncertainty in seismic inversion. There are many flavours of gradient-based MCMC; here, we will only focus on the Unadjusted Langevin algorithm (ULA) and Metropolis-Adjusted Langevin algorithm (MALA). We propose an adaptive step-length based on the Lipschitz condition within ULA to automate the tuning of step-length and suppress the Metropolis-Hastings acceptance step in MALA. We consider the linear seismic travel-time tomography problem as a numerical example to demonstrate the applicability of both methods.
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A New Integrated Workflow to Generate Avo Feasibility Maps for Prospect De-Risking
Authors P. Avseth, I. Lehocki, K. Angard, T. Hansen, E. Shelavina and S. SchjelderupSummaryA new integrated workflow for generation of AVO feasibility maps to be used in prospect de-risking is presented. We demonstrate the workflow on data from the Barents Sea. The methodology enables rapid extrapolation of expected rock physics properties away from well control, along selected horizon, constrained by seismic velocity information, geological inputs (basin modelling, seismic stratigraphy and facies maps) and rock physics depth trend analysis. The workflow should allow for more rapid, seamless and geologically consistent DHI de-risking of prospects in areas with complex geology and tectonic influence. The AVO feasibility maps can furthermore be utilized to generate non-stationary training data for AVO classification.
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Rock Physics Analysis of Volcanic Lava Flows and Hyaloclastites
Authors P. Avseth, J. Millett, D. Jerram, S. Planke and D. HealySummaryA study is conducted to investigate the rock physics properties of volcanic facies from available core measurements (72 samples available from Iceland and Hawaii). The main goal is to investigate the rock physics properties of a set of volcanic rock samples, and to establish predictive rock physics templates for these rocks, as a function of facies and rock texture, fluids and minerology. We focus on lava flows and hyaloclastites from Iceland and Hawaii. We find that both these facies can be modelled using modified Hashin-Shtrikman upper elastic bounds, and we create rock-physics templates for varying porosity and fluid saturations. Dry or gas-filled hyaloclastite facies plots with low acoustic impedances and low Vp/Vs ratios and are nicely separated from brine-filled hyaloclastites. Dry and wet high-porosity/high-permeability vesicular lavas will have similar AI and Vp/Vs values, and therefore these rocks will be more difficult to discriminate seismically.
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