Browsing by Author "Chesnokov, Evgeni M."
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Item A Computational Library for Determining the Mechanical Properties of Crystals and Polycrystalline Aggregates(2018-12) Torlucci, Anthony 1983-; Castagna, John P.; Chesnokov, Evgeni M.; Smith, TadComputer modeling of the basic equations of solid mechanics is simplified with a well designed computational library. The weighted arithmetic average and weighted harmonic average are abstract forms of the more concrete upper and lower bounds for the effective elastic moduli of fluid mixtures and solid composites. More rigorous upper and lower bounds for the effective isotropic elastic coefficients of an anisotropic crystal are calculated from the two linear fourth rank tensor invariants. Rock physics transform functions for isotropic homogeneous materials can be used to calculate the compressional wave velocity and shear wave velocity from the mean value of the upper and lower bounds yielding a spherical surface in the three dimensional phase velocity space. The behavior of the velocity surface for a given anisotropic tensor, however, is not easily recognized in the analytical form of the Green-Christoffel equation. The phase-velocity surface for a single crystal deviates from the isotropic velocity due to the inherent nature of the crystal being anisotropic. The amount of deviation and curvature of the surface depends on the symmetry and the values of the stiffness tensor. A generic library of data structures and algorithms makes visualizing and interpreting these results simpler.Item A Relation Between Adiabatic and Isothermal Moduli(2014-05) Myziuk, Nicholas Karl 1986-; Chesnokov, Evgeni M.; Kouri, Donald J.; Hall, Stuart A.Exploration in shale formations has experienced substantial popularity growth in recent history. With this, the importance of understanding the elastic properties of the sub-surface in exploration areas has also grown. Dynamic elastic properties can be extracted from seismic or well log velocity information; however for geomechanical modeling purposes, it is often desirable to obtain static measurements directly from core samples. Accurate static measurements are of significant importance to many applications, namely hydraulic fracturing and reservoir engineering, and are often used to determine reservoir behavior in completions engineering. Widely unavailable or not properly preserved core data has resulted in the development of correlation functions to relate dynamic and static measurements for estimation of static rock properties in exploration regions where static data are not available. The relationship between static and dynamic measurements of both Poisson’s Ratio and Young’s Modulus has attracted some interest with regard to exploration, and has even been proposed as a product indicator for shales. This work is targeted at investigation of this relationship from the perspective of thermodynamics. Results here provide a schematic for relating adiabatic and isothermal measurements of elastic properties in shales and various aggregates, and the effect due to anisotropy. This method uses elastic velocity data to extract the adiabatic material properties, coupled with compositional information and thermal characteristics for estimation of the isothermal material properties. Variation due to anisotropy is examined by manipulating the tensor of thermal expansion for the isothermal calculations. Analysis was conducted for several core samples found throughout the referenced literature for Barnett, Haynesville, and Bossier shales. Results of this work conclude only a qualitative understanding of the extent to which static properties can be estimated via the adiabatic-isothermal relationship. As such, the developed formulae described here do not accurately depict the differences between static and dynamic deformation, and consequently cannot be used for estimation of static properties from dynamic measurements as originally hypothesized. Further developments in this area may provide an alternative mechanism for estimation of these properties.Item A study of frequency dependent analyses on Stratton Oil Field, South Texas.(2012-05) Ahmed, Hazem; Castagna, John P.; Goloshubin, Gennady M.; Schneider, Robert; Chesnokov, Evgeni M.Frequency dependent analysis has been utilized recently by the industry. It allows the seismic interpreter to see features that could not be clearly seen when dealing with the whole frequency band. This could be related to bed thickness, lithology, or physical properties of the reservoir. Stratton Oil Field was discovered in 1937, and it is well known to be a highly productive area. At the level of Oligocene Frio Formation, the Stratton field is defined by multiple NW-SW trending structures like most of the reservoirs along the Gulf of Mexico. The Frio formation is divided into upper, middle, and lower segments. Our study zone lies in the middle and lower segments. Conventional analysis processes were applied, such as; AVO, inversion, and LMR transform. The investigated zone showed different behavior at each stage of the investigation. Thus, we suggested utilizing a frequency dependent technique to investigate the dataset. Frequency dependent amplitude analysis was utilized, where anomalous behaviors were indicated at the reservoir zone. Further frequency dependent analyses showed the same anomalous behavior at the reservoir zone. The low frequencies could map the reservoir zone much more obviously, where the anomalies on every stage of the analysis had the same behavior that corresponds to the same zone. Frequency dependent analysis can help the seismic interpreter to better understand the reservoir characteristics, and can help to map the reservoir anomalies in a better way.Item AN APPLICATION OF FLUID MOBILITY ATTRIBUTE FOR PERMEABILITY PROGNOSIS WITHIN THE MIDDLE JURASSIC SEDIMENTS IN THE SOUTHERN PART OF WESTERN SIBERIA(2015-05) Rusakov, Pavel 1988-; Castagna, John P.; Goloshubin, Gennady M.; Chesnokov, Evgeni M.; Ren, HaitaoThe study area is located in the southern part of Western Siberia. The main hydrocarbon productivity in this area is related to the middle Jurassic Ju3-4 formation. The target interval is laterally changeable and characterized by weakly anisotropic sandstones with interbedded coal and shale. As a result, there are difficulties in predicting the lateral variations of the transport properties in the Ju3-4 formation. For solving this problem, the dataset of the 3D seismic and well data (core samples, well logs, and formation testing) was utilized. The core measurements of the permeability at room conditions show a weak anisotropy in orthogonal directions and a correlation with porosity. The porosity values in scale of the well log were calculated based on the relative αSP anomalies, accounting for temperature and pressure formation conditions. Permeability in the same scale was predicted based on the porosity values and Kozeny-Carman’s formula. The comparison of permeability from core samples and permeability from well logs illustrates some similarities. For prognosis of the formation permeability in a cross-well space a seismic attribute proportional to fluid mobility was calculated. The attribute is the result of first derivatives of reflection coefficient from a permeable boundary with respect to frequency. Based on the relationship between the attribute values and the average permeability of the formation in the wells, the average formation permeability map was constructed. The map is in the accordance with known production rates in the wells.Item An Investigation of Seismic Reflectivity Spectra, Moments, and Fractal Dimensions(2021-08) Amirzadeh, Maria; Castagna, John P.; Chesnokov, Evgeni M.; Ebrom, Daniel A.; Wang, GuoquanStatistical models for seismic reflectivity spectra provide means of generating numerical reflection sequences as a priori information for seismic inversion, to test geophysical data processing techniques, and to parameterize real reflection sequences for classification purposes. I tested the effectiveness of using parametric and non-parametric statistical methods to estimate optimized reflectivity spectra and to identify the accurate form of the reflectivity distribution of seismic and well log data that best simulates observations. I show that a sum of generalized Gaussian distributions with variable mean, variance, skewness, and kurtosis characterizes measured distributions well. Reflectivity series distributions derived from sonic and density logs in 180 wells from 8 basins worldwide at forty sampling intervals between 0.1 milliseconds and 4 milliseconds show that the reflectivity exhibits a range of spectral shapes, from white to blue. The variation is strongly dependent on the sampling rate which has a remarkable effect on the shape of reflectivity distributions, spectra, and designed deconvolution filters. The sample rate dependence of spectral shape and the earth impulse response is greatly affected by internal multiples and transmission losses. Reflectivity moments and spectra vary with digital sampling interval and thus do not characterize a continuous earth well. I develop a novel technique whereby moments and spectral parameters are extrapolated to zero sample rate.Item Application of Constrained Least-Squares Spectral Analysis(2014-05) Oyem, Arnold Gideon 1978-; Castagna, John P.; Li, Aibing; Chesnokov, Evgeni M.; Gebretsadik, EshetuConstrained Least-Squares Spectral Analysis (CLSSA) is applied to seismic data for (1) stratigraphic layer thickness estimation, (2) stratigraphic visualization, and (3) Hydrocarbon indication. Results obtained from these analyses are compared with similar analyses from Continuous Wavelet Transform (CWT) and Short Time Window Fourier Transform (STFT), to access improvements on time-frequency resolution associated with these analyses. Results from time frequency analysis of CLSSA spectrum, show apparent time thicknesses that strongly correlate with true stratigraphic thicknesses, demonstrated first from model data and then applied to real seismic data. Conversely, the spectrum of STFT shows underestimation of true stratigraphic thicknesses as a result of spectral smearing. Amplitude maps derived from analyzing the spectra of these methods show CLSSA to reveal more subtleness of hidden stratigraphic features in the seismic data as a result of high amplitude contrast between the stratigraphic features and the background. The spectrum of STFT suffers the limitation of poor amplitude contrast between the target feature and the background as a result of extraneous spectral energy smeared on the horizon. CWT shows a major setback arising from the duo temporal behavior within the data bandwidth. Analysis of CLSSA amplitude spectrum in hydrocarbon fluid-saturated porous medium also indicates strong anomalous amplitudes in the hydrocarbon zone with respect to background brine saturation comparative to CWT and STFT. These analyses demonstrate that spectral decomposition using CLSSA approach has superior time-frequency resolution to CWT and STFTItem Applications of Composite Frequency-Based Seismic Discontinuity Attributes for Robust Fault and Fracture Detection in a Bandwidth-Extended 3D Seismic Dataset in the Paradox Basin, Colorado(2016-05) Sierra, Jose Antonio 1986-; Castagna, John P.; Chesnokov, Evgeni M.; Kayali, AminBandwidth-extension of a 3D seismic dataset from the Paradox Basin in Colorado showed a two-fold improvement in vertical resolution that allows for the interpretation of very subtle lateral discontinuities using seismic attributes. Common seismic discontinuity detecting attributes like coherence, chaos and curvature showed a noticeable increase in fault detection when applied on bandwidth extended data as compared to the original seismic data. A composite attribute was calculated by running these conventional attributes on various frequency band outputs from spectral decomposition and combining them using principal component analysis. This composite attribute can much more reliably delineate and locate very subtle faults compared to the individual input attributes. Validating the different conventional discontinuity attributes and the composite attribute against the seismic amplitude data showed that the subtle faults picked up by the composite attribute correspond to geologically-realistic faint discontinuities that are below the noise level of any of the input attributes alone. The orientations of seismically derived faults were validated by comparing them to faults seen at nearby wells. The reduction of noise and increase in spatial resolution allows for a reliable calculation of a fault density attribute. This attribute was compared against rock physics inclusion models through elastic inversion for quantitative interpretation of fractures in the seismic data showing a relationship between the presence of faults, the concentration of fractures, and the saturating fluid.Item Applying Maxwell's EM Equations in the Low-Frequency Limit to Earth Investigations(2021-05) Neese, John Wesley; Castagna, John P.; Chesnokov, Evgeni M.; Jackson, David R.; Thomsen, Leon; Zheng, YingcaiStandard seismic-processing methods have been applied to numerical simulations for several variations of a standard 1D numerical ISEM model. These calculations were justified by the mathematical similarity between dynamical equations in elastodynamics and electromagnetics, and demonstrated that, in simple cases, numerical ISEM data, appropriately acquired, and processed seismic-style, can be interpreted for subsurface effective resistivity. Previous 1D results are extended in the first section of this dissertation to numerical simulations for a 2.5D numerical ISEM model. Common shot gathers, common offset gathers, CMP gathers, and a proposed Q-compensated “resistivity moveout” correction show promise as indicators of resistivity variations in the subsurface. Naturally, the mathematical similarity is limited by essential differences between the physical quantities described in elastodynamics (underlying seismology) and electromagnetics. I explore these limits by defining an analogy between elastodynamic displacement and electromagnetic electric vector potential. Finally, I present a novel analytical solution for the problem of radiation emanating from an arbitrarily-oriented dipole and scattering from an infinite cylinder in 3D space. I then use the solution to perform a numerical study of crosshole electromagnetic tunnel detection.Item ASSESSMENT OF AZIMUTHAL VARIATIONS IN DEPTH MIGRATED MARINE WIDE-AZIMUTH DATA: WORKFLOW DERIVATION AND EXAMPLES FROM THE EAST BREAKS REGION OF THE GULF OF MEXICO(2012-12) Sosa, Armando 1981-; Zhou, Hua-Wei; Whitmore, N. Daniel; Chesnokov, Evgeni M.; Thomsen, LeonCurrent seismic acquisition geometries are designed to record a broader range of azimuths. While illumination of subsalt structures is a major factor when planning these surveys, azimuthal variations due to heterogeneity and anisotropy can also significantly impact the imaging of these targets if they are not well understood. This study presents a practical workflow for detecting and assessing the significance of azimuthal variations on wide-azimuth data, in an effort to start to better utilize the azimuthal aspect of this type of survey. The assessment itself was performed in depth migrated images of wide-azimuth data from the East Breaks region of the Gulf of Mexico, which were decomposed into azimuth-sectored angle-domain gathers post-imaging. This data domain provided great flexibility to the analysis of azimuthal moveout anomalies, as different subsets of common angle volumes were evaluated depending on their level of contributions to the imaging of a given geologic target. As the derived workflow was tested in different scenarios, it became clear that analyzing a variety of attributes, volumetrically or at specific interpreted horizons, delivered qualitative results that confirmed the presence of azimuthal variations and how irregular or chaotic these were, depending on the area of interest. Throughout this study, it was quite important to develop quality control plots that aid the validation of the propose techniques. Particularly significant were the cross-correlation azimuthal residual maps and the attributes used to rule out whether an azimuthal anomaly was being induced by the migration models, since improving the fitting of the data by using a higher order of symmetry system was outside of the scope for this study. It was also concluded that while the resolution of the dataset used in this study was typical for depth migration images in the region, it was not ideal in terms of frequency and azimuthal sampling. However, this analysis did provide multiple insights into the intricacies of assessing azimuthal variations in image space.Item Azimuthal P-wave AVA Inversion for Fracture Orientation and Density(2014-05) Xia, Keyao 1990-; Li, Aibing; Hilterman, Fred J.; Chesnokov, Evgeni M.; Zhao, ZhiyongThis thesis studies the numerical seismic modeling of a simulated fractured medium to analyze variations of seismic reflection amplitudes with incident and azimuthal angles (AVAZ). The intent is to extract the information about the fracture orientation and intensity of a fractured medium. The effective compliance tensor for a fractured medium can be written as the sum of the compliance tensor of the unfractured background rock and the compliance tensor for the set of aligned fractures. Based on the assumption of rotationally invariant fracture sets, two fracture compliances—the normal and tangential compliance—are required to specify the fracture compliance tensor. The stiffness tensor can be attained by inverting the compliance tensor. The P-wave reflection coefficients for arbitrary anisotropic media are obtained by two methods (Chattopadhyay, 2004; Schoenberg and Protazio, 1992). Rüger’s linear approximation can accurately estimate the exact reflection coefficients and hence it is widely used in the linear inversion. Analysis is applied in the decision to choose between the incident angle and the average angle for Rüger’s linear approximation. Linear AVAZ inversions, based on singular value decomposition (SVD), and non-linear AVAZ inversion, based on generalized linear inversion (GLI), for fracture orientation and HTI anisotropy parameters, were applied on P-wave reflection coefficients with variable incident angle and azimuth. However, 90˚ ambiguity in the estimation of the fracture orientation always exists. Sensitivity analysis of the inversion results, including S/N ratio, maximum incident angle used, and error propagation, confirms the accuracy of the amplitude analysis.Item Borehole Seismic Methods: Estimating Anisotropy And The Distributed Acoustic Sensing (DAS) To Geophone Transformation(2023-05-07) Sayed, Ali Yawar; Stewart, Robert R.; Chesnokov, Evgeni M.; Zheng, Yingcai; Kumar, DhananjaySeveral vertical seismic profile (VSP) methods are addressed with the aim of improving accuracy of the results or extracting new insights from the data. An effective horizontal transverse isotropy (HTI) framework was built to relate Thomsen’s parameters to fracture density and fracture fluid. Direct shear energy present on the horizontal components of vertical-vibrator zero-offset VSP data on two field data examples was used to characterize the fast-shear azimuth along well depth. Parametric wavefield decomposition was used for the strong anisotropy case and the rotation-correlation method was adapted for the weak anisotropy case. The results correlated with independent log measurements and studies. Synthetic signatures of azimuthal VSP data generated from weakly, moderately, and heavily fractured model show that fracture response of dry fractures is stronger than that of fluid-filled fractures. Similar signatures using a dipping interface within isotropic and fractured models show that isotropic subsurface structures can produce an apparent fracture response and they can distort the true fracture response. A structure-consistent orientation workflow was developed to correct for the structural effect and uncover the true fracture response. Beyond conventional VSPs, a transformation was developed to convert distributed acoustic sensing (DAS) measurements to conventional velocity/acceleration measurements. A theoretical framework was developed to show that DAS data are inherently filtered in spatial frequency and amplitude. Synthetic and field data examples are analyzed to show that DAS measurements have a detrimental effect on traveltime picking, Q-estimation, and imaging. These effects are negated by the DAS-to-velocity transform. The methods developed in this dissertation are being actively used to deliver commercial products in the field.Item Case Study: Locating Productive Layers using Pair-Correlation Function in Volve Field North Sea(2019-05) Zerr, Jackson Jay 1993-; Chesnokov, Evgeni M.; Lapen, Thomas J.; Hall, Stuart A.; Gassiyev, AslanA stratigraphic interval with a high probability of containing hydrocarbons and ideal permeability for extraction is actively sought in energy exploration and production. Finding this true productive layer would prove both efficient and economical for drilling and production. This study uses log data from wells within the Volve, North Sea as input data for Pair Correlation Function (PCF) analysis, an application of the Effective Medium Theory (EMT). This approach has the potential to predict a productive layer and physical properties of a reservoir. In the study, calculations are performed over multiple well logs as a test of the approach and to assess the accuracy of the predictions, which are confirmed by production data and geologic interpretations. Based on the PCF results, this approach predicted a productive layer with 81% accuracy within the analyzed wells in the Volve field. Given these promising results, PCF calculations could be a new method, used in conjunction with other reservoir characterization techniques, to better predict a productive layer.Item Case Study: Relationship between Correlation Radius and Permeability, Volve Field, North Sea(2020-05) Suen, Conrad; Chesnokov, Evgeni M.; Lapen, Thomas J.; Metwally, Yasser M.A productive layer is a stratigraphic interval that is prone to contain hydrocarbons with physical parameters favorable for production or extraction. Using the pair correlation function (PCF), a method of Effective Medium Theory (EMT), nine sets of amplitude and correlation radii were determined. These values were then analyzed with permeability (mD) at a given depth in measured depth (ft) to determine relationships between correlation radius and permeability over the productive layer. Previous work completed determined low correlation radius relates to a high amplitude in which a productive interval can be predicted. As permeability is essential for a successful reservoir, high permeability values are expected in such productive intervals. By understanding the relationship between permeability and correlation radius over a productive interval, the determination of defining a productive reservoir interval is increased with knowledge from well log data. Results of this study support the hypothesis that relative high permeability values are synonymous with relative low correlation radii and allow for another analog in which the productive interval can be determined. The goal of this study is connected to the potential to show the link between measured characteristics (amplitudes and radii of various correlation functions) and unmeasured characteristics (permeability).Item Characterization of Depositional Layering Based on Spectral Seismic Interpretation(2017-08) Meza, Ramses G. 1975-; Castagna, John P.; Chesnokov, Evgeni M.; Zheng, Yingcai; Florez, Juan M.Depositional sequences layering parameters such as net-to-gross ratio can affect seismic signatures and their frequency spectra. Various means of estimating net-sand thickness were tested in an oil field with sufficient well penetrations providing known thicknesses to evaluate the seismic predictions. Map-based detuning of the signal strength in proportion to the net-to-gross ratio allowed statistically significant estimates of net-sand thickness. The impedance-based Seismic Ney-Pay method resulted in more accurate estimates (mean absolute prediction error at well validation locations under 3.0 m ± 1.5 m) than those of a reflectivity-based detuning method (4.0 m ± 2.7 m) or multiple linear regression (5.9 m ± 5.8 m); the latter with weak statistical significance. Time-frequency and time-phase analysis showed that for a thin-bed in a binary-impedance setting, there is no observable sensitivity in preferential illumination as NTG changes, while mutual thin-bed interference can significantly change the preferred phase component for each participating target. This phenomenon is largely driven by the embedded seismic wavelet, which determines the nominal seismic response of an isolated thin layer and what phase component would preferentially illuminate it. The joint time-frequency and time-phase analysis applied to field seismic data resulted in a new interpretation of the syn-depositional character of secondary faults cutting the reservoir; raising the possibility of lateral changes in reservoir quality that had not been previously recognized. Forward modelling of depositional sequences yielded P- and S-wave impedances and broad-band reflectivities whose time-invariant spectral magnitude responses follow a power-law of frequency. This allowed using some fractal statistics to relate the spectral magnitude attributes with changes in the underlying layering characteristics, such as the empirical parametrization of the Cumulative Distribution Function. Weak global empirical correlations were found between spectral magnitude attributes and layering parameters when using a limited well-log database. Spectral-magnitude attributes were calculated for a field 3D seismic survey at each trace location for each calculated reflectivity wave mode, with poor statistical significance for correlations between these spectral-magnitude attributes and the layering parameters estimated at the collocated wellbores. These results are inconsistent with the broad-band forward modelling results.Item COMPARISON AND INTEGRATION OF FREQUENCY MULTIATTRIBUTTES IN THIN LAYER VISUALIZATION: A STRATTON FIELD CASE STUDY(2014-05) Atekpa, Musa Ibrahim 1982-; Castagna, John P.; Chesnokov, Evgeni M.; Kouri, Donald J.THE CHOICE OF THE RIGHT WINDOW SIZE IN SPECTRAL ANALYSIS HELPS TO CAPTURE THE BEST THICKNESS VARIABILITY ASSOCIATED WITH TUNING EFFECTS IN THIN LAYERS.THIS RESEARCH IS A FIDELITY COMPARISON BETWEEN SPECTRAL DECOMPOSITION METHODS SUCH AS DISCRETE FOURIER TRANSFORM (DFT), CONTINUOUS WAVELET TRANSFORM (CWT) AND CONSTRAINED LEAST SQUARES SPECTRAL ANALYSIS (CLSSA), WHICH IS AN INVERSION- BASED ALGORITHM THAT COMPUTES SPECTRAL DECOMPOSITION. RESOLUTION OF A 'D' SAND SERIES CHANNEL IN FILL SANDSTONE WITH SPLAY DEPOSITS OF THE MIDDLE FRIO FORMATION IS SUPERIOR USING THE INVERSION METHOD AT DIFFERENT ANALYSIS WINDOWS. INTEGRATION OF THE ATTRIBUTES IS DONE IN A SYNERGISTIC MANNER TO GO BEYOND THE LIMIT OF SPECTRAL DECOMPOSITION USING MULTIVARIATE ANALYSIS TO VISUALIZE SUBTLE FEATURES. AT SMALLER SPECTRAL DECOMPOSITION ANALYSIS WINDOW AND LARGER PRINCIPAL COMPONENT ANALYSIS (PCA) WINDOWS RESPECTIVELY, RESULT SHOWS THAT THE FOURIER METHOD, THOUGH HAVING A FLUCTUATING HEISENBERG UNCERTAINTY PRODUCT AT PEAK SPECTRAL FREQUENCIES, PRODUCES AND ENHANCEMENT BEYOND THE SPECTRAL DECOMPOSITION BANDWIDTH LIMIT DUE TO STRONGER CORRELATION OF THE ATTRIBUTE FREQUENCIES AFTER AXIS ROTATION IN ITS PRINCIPAL COMPONENTS. FINALLY, THE MULTIPLICITY OBSERVED IN THE ENERGETIC TRENDS OF THE FREQUENCY SPECTRA IS COMBINED TO ENHANCE THE STRATIGRAPHIC FEATURES USING PRIMARY COLORS.Item Comparison of Pre-stack Noise Suppression Techniques for AVO Analysis(2012-12) Liu, Dong 1982-; Castagna, John P.; Chesnokov, Evgeni M.; Portniaguine, OlegSynthetic study has proved that post-stack Structural Filter (SF) applied to Common Offset (CO) gathers with pilot-stack showed better performance over FK Dip Filter and FX Decon with regard to fault preservation, noise suppression, and amplitude preservation; in Common Midpoint (CMP) domain, Radon Filter and Structural Filter suppressed random noise, spikes, and multiples with high efficiency. SF with padded intercept was superior to Radon Filter, because it preserved the reflection amplitude with offset variation. The application of Structural Filter in Stratton Field data showed that the best workflow was the cascaded process. The cascaded SF has been demonstrated to be superior over conventional noise suppression methods, because it preserved relative amplitude, removed random noise, flattened seismic reflectors, and enhanced faults and fractures. In addition, by applying Structural Filter to pre-stack time migrated gathers, the improved velocity produced better stack sections for further structure identification and interpretation. Using the conditioned CRP gathers in AVO analysis, it improved intercept and gradient sections and AVO cross-plot. The intercept and gradient sections showed negative intercept and gradient for top reservoir sand, indicating a class III AVO response. AVO cross-plots showed that SF defined a clustered background trend which allowed us to differentiate deviations associated with top and base of the reservoir. Both synthetic study and real data application proved that SF is an AVO compliant noise suppression technique, and is a great tool for AVO data conditioning. The application of Structural Filter in Stratton Field data for AVO analysis may potentially help to find new prospect for exploitation and production in the Gulf Coast Basin.Item Compressional-To-Shear-Wave Velocity Ratio in Organic Shales and Acoustic Dispersion in Low Permeability Unconventional Reservoir Rocks(2019-12) Omovie, Sheyore John 1977-; Castagna, John P.; Chesnokov, Evgeni M.; Zheng, Yingcai; Myers, Michael T.In situ P-wave and S-wave velocity measurements in a variety of organic-rich shales exhibit compressional-to-shear-wave velocity ratios that are significantly lower than lithologically similar fully brine-saturated shales having low organic content. It has been hypothesized that this drop could be explained by the direct influence of kerogen on the rock frame and/or by the presence of free hydrocarbons in the pore space. Theoretical bounding equations, using pure kerogen as an end-member component without associated gas, indicate that kerogen reduces both the P-wave and S-wave velocities but does not in general reduce their ratio. The theoretical modeling is consistent with ultrasonic measurements on organic-shale core samples that show no dependence of velocity ratios on kerogen volume alone. Sonic-log measurements of compressional and shear-wave velocities in seven organic-rich shale formations deviate significantly from the Greenberg-Castagna empirical brine-saturated shale trend towards lower velocity ratios. In these formations, and on core measurements, Gassmann fluid substitution to 100% brine saturation yields velocity ratios consistent with the Greenberg-Castagna velocity trend for fully brine-saturated shales, despite the high organic content. These measurements, as well as theoretical modeling, all suggest that the velocity-ratio reduction in organic shales is best explained by the presence of free hydrocarbons. The limitation of the Greenberg-Castagna shear-wave velocity prediction method when applied to organic-rich shales has been resolved, by modifying the original Greenberg-Castagna algorithm. The modified workflow accurately predicts shear-wave velocity for seven organic-shale formations with appreciable solid organic matter to within ±1% percent mean error. For a number of low-permeability well-lithified shales, utilizing laboratory measurements on dry and fully brine-saturated samples as well as comparing to log data and theoretical modeling, we find no statistically significant intrinsic dispersion from seismic to sonic and laboratory-measurement frequencies due to fluid effects. At in situ stress conditions, the Gassmann zero-frequency P-wave velocity prediction for a Permian-basin sample was within 0.2% to 2.2% of the measured velocity on the brine-saturated sample at ultrasonic frequency. Based on the Biot-Gassmann model, the characteristic frequency occurs at about 10^10 Hz. Applying a squirt-flow model also predicts a transition to the high-frequency regime occurring at about 10^9 Hz.Item CONNECTION OF ELASTIC AND TRANSPORT PROPERTIES: EFFECTIVE MEDIUM STUDY IN ANISOTROPIC POROUS MEDIA(2013-05) Jiang, Tao 1982-; Chesnokov, Evgeni M.; Castagna, John P.; Goloshubin, Gennady M.; Kouri, Donald J.The elastic property of a porous medium is closely related to the elastic properties of all the components, such as stiffness, density, orientation distribution, and the microstructure properties, such as porosity, pore shape, and pore connection. On the other hand, the permeability doesn’t feel the properties of solid matrix and is closely related to the transport properties of the pore fluid and microstructure properties. Therefore, the permeability can be correlated to the elastic properties when we neglect the effect from the matrix. A first attempt has been made to investigate the different influence from microstructure to the elastic property and permeability, using General Singular Approximation (GSA) effective medium theory. The GSA method takes into account the pore connection of the microstructure in porous media by the friability parameter. In this dissertation, first the microstructure properties of Barnett shale have been obtained by GSA inversion; second a GSA-based fluid substitution method has been introduced. The results are given for different pore connection and compared with Gassmann substitution; third and the most important, the GSA method has been used to model both the effective stiffness and effective permeability for the same model at the same time. Thus a series of GSA modeling has been done for the full range of friability and porosity in isotropic and anisotropic models, as a result, three categories of the correlations have been discovered: (1) the correlation between microstructure properties and the elastic properties, including stiffness tensor, Thomsen parameter, velocities, and Biot’s alpha parameter; (2) the correlation between microstructures properties and the permeability; and (3) the correlation between the permeability and the elastic properties, which shows nearly linear relation in the direction parallel to cracks, and hyperbolic relation in the direction vertical to cracks.Item CONVEX HULL METHOD FOR SRV ESTIMATION(2014-05) Lombardi, Michael Edward 1982-; Chesnokov, Evgeni M.; Kouri, Donald J.; Li, AibingThe prevalent use of induced hydraulic fracturing, commonly known as fracking, in reservoirs for shale gas demands that changes in geophysical properties within the fractured rock be studied. Hydraulic fracturing events typically take place over several hours. During this time, the seismic anisotropy of the reservoir rapidly changes. These dynamic seismic velocities can be modeled from reservoir attributes and properties that change during the fracking process. One such dynamic property is the stimulated reservoir volume (SRV) which has been investigated using the Cube and Surfer methods (Adejuyigbe, 2013). For this thesis, we present a new method for modeling the SRV based on minimum convex hulls. This method was implemented and tested using data from the Dollie Thorell Well in the Barnett shale in North Texas. Results from those tests show that the convex hull method is robust at modeling scattered microseismic event sets of spherical or cylindrical character. For these microseismic event sets, this modeling technique yielded a logarithmic increase in stimulated reservoir volume over time. The minimum convex hull method was implemented as a module within a 4D software framework to allow for the uniform data representation, processing flow, and visualization of future research methods. This work provides a starting point for SRV estimation research by investigating the minimum convex hull method while delivering effective 4D tools for future SRV estimation studies.Item Correlstion between the volume of slurry and the volume of fracture in Barnett Shale(2013-08) Adejuyigbe, Olawale John 1974-; Chesnokov, Evgeni M.; Goloshubin, Gennady M.; Leite, RenatoMicroseismic fracture mapping has revealed that large fracture networks can be generated in many shale reservoirs and create multiple of plan complex structure. The ultra-low permeability in Barnett shale requires hydraulic fracturing to generate wellbore contact with the reservoir in order to achieve economic gas rates by the concept of a single fracture half-length. This is the reason for using fracture half-length of the hydraulic fracture area dimensions through the total fracture network length to estimate the volume of hydraulic fracture from a Dollie Thorell IV well in Barnett Shale. All data were released by Devon Energy for the purpose of this study. As a way to better evaluate the effective producing network of the shale reservoir, Surfer VI and discrete bin method were used to estimate of the volume of hydraulic fracture. The results of the analyses from Surfer VI were from (i) Trapezoidal rule; and (ii) Simpson’s rules, which gave an average result of 6.7 x 1010 cubic ft, the discrete bin method was calculated from the equation of fracture network half-length where length (2xf) and width (xn) represented the fracture spacing in the shale reservoir. The discrete bin method analysis gave a total result of 6.7 x 1010 cubic ft; this is the estimated figure for the volume of hydraulic fracture in very tight reservoirs. The correlation between the volume of slurry and the volume of the hydraulic fracture will establish the crack density. The graphic result of the correlation between the volume of slurry and the estimated volume of fracture showed that the crack density increases when the volume of the fracture increases. The crack density is always less than 1 due to leak-off of fracturing fluid into the reservoir during the hydraulic fracturing treatment.