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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
1 - 20 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
Authors 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
Authors P. Dell’AversanaSummaryIn 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
Authors M. Mehboob GillSummaryThe 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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