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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
1 - 50 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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