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The successful production of unconventional resources such as shale gas is highly dependent on its two reservoir properties, organic matter and rock brittleness. High resolution spatially characterization of these two unconventional reservoir properties needs surface reflection seismic data. However, to delineate these two parameters on seismic scale is a challenging task because poor correlation is observed between these parameters and elastic properties of the rock. To encounter this adversity in current study we proposed effective attributes method in which organic shale reservoir properties are divided into their hard and soft elastic response. From the analysis of worldwide laboratory dataset, we find that hard and soft components have shown us much better linear correlation with P- and S- wave impedance. The proposed effective attributes, helped us to reduce the gap between unconventional reservoir properties and seismic characteristics. These attributes are the main controlling factor for rock elastic properties and exhibit information about hydrocarbon generation capacity and rock brittleness. A well data example from Sembar shale has also shown successful results for proposed effective attributes methodology. These attributes application on inverted P-wave impedance seismic data of employed organic shale reservoir have shown productive results to quantify its unconventional prospect on seismic scale. The approach used in this study can be confidently employed to assess unconventional reservoir potential in other parts of the world. [ABSTRACT FROM AUTHOR]

The elastic properties of argillaceous sandstones are significantly controlled, however, by the perplexing distribution of dispersed, cemented and matrix (including structural and layered) clay. The corresponding rock physics models are established to investigate the influence of different clay distribution on the elastic properties of sandstone. The rock physics modelling and laboratory experimental results exhibit that the higher the content of the matrix clay, the lower the elastic wave velocity. The dispersed and cemented clay increases the sandstone's velocity by reducing the porosity; the increase of dispersed clay only causes a slight increase in the elastic wave velocity in sandstone. In contrast, a small amount of cemented clay can significantly increase the velocity in sandstone. Based on these understandings, we construct a cross‐plot of P‐wave velocity and clay content as a template to diagnose clay distribution. Based on the rock physics model and empirical knowledge, we divide the template into four zones, namely, matrix, dispersed, cemented and mixed clay distribution zones. Then, we use the published experimental data and numerical modelling data to validate the template. Based on diagnosing the clay distribution, we introduce how to use the diagnostic results of the template to select a suitable rock physics model for argillaceous sandstone in Shengli Oil Field, East China. The selected rock physics model, guided by diagnosing the clay distribution, predicts P‐ and S‐wave velocity very well. The proposed rock physics template for diagnosing clay distribution also has potential application in well‐logging data interpretation, rock physics modelling and reservoir characterization. [ABSTRACT FROM AUTHOR]

Understanding and modeling the elastic and anisotropic responses of organic shale is crucial for interpreting sonic and seismic data, and hence play a vital role in many fields of Earth and Energy science such as hydrocarbon source rock evaluation, reservoir characterization of unconventional shale plays, cap rock assessment for geological storage of CO 2 and nuclear waste disposal. The thermal maturity level significantly controls the geochemistry signature, geological characteristics and geophysical responses of organic shale. We review the rock physics modeling that links the geological feature with elastic responses of organic shale in general. However, current rock physics modeling of organic shales either ignore or qualitative consider the effects of thermal maturity. To construct a quantitatively maturity-constrained rock physics model for shale, we review the evolutionary characteristics of two types of organic matter (kerogen and bitumen) and organic porosity during thermal maturation. We summarize and quantitatively characterize the maturity-dependent elastic properties of organic matter and fluids. We propose a joint geochemistry-rock physics modeling that use various effective medium theories to quantify the effects of thermal maturity level (Vitrinite reflectance, % R o) on the elastic signatures of inorganic frame, fluids filled porous organic matter as well as their elastic interactions. In particular, the role of kerogen and bitumen on the elastic properties of the organic shale are separately incorporated into the rock physics modeling. The developed rock physics model demonstrates that reservoir parameters (e.g. TOC, porosity and clay content) have distinct impacts on the elastic and anisotropic behaviors of shale reservoirs at different maturity levels. We also use several ultrasonic and sonic logging data sets at various maturity levels, including Jimsar shale formation in NW China, Qingshankou shale formation in NE China and Longmaxi shale formation in SW China, to benchmark the effectiveness of the proposed model. The modeling results show satisfactory agreement with the P-wave velocity, S-wave velocity, density, P-wave anisotropy magnitude, and S-wave anisotropy magnitude, only when the appropriate maturity level is given, illustrating the importance of combining organic geochemistry with rock physics modeling. We also discussed the influence of organic matter morphology, the degree of clay alignment as well as overpressure-induced micro-fractures on the elastic and anisotropic responses of organic shale, which can be also considered within the developed rock physics modeling framework. [ABSTRACT FROM AUTHOR]

By evaluating the consistency of the Gassmann theory with various inclusion‐based effective medium theories, we investigate the impact of elastic interactions between ellipsoidal pores on the poroelasticity. To rule out any factors that can violate the Gassmann condition, other than elastic interactions, we first construct idealized models that contain only a single set of isolated, identical, and vertically aligned ellipsoidal pores. The numerical simulation suggests that the periodic distribution of ellipsoidal pores generate uniform pore pressure distribution, whereas random distribution of ellipsoidal pores generates heterogeneous pore pressure distributions. Then we analyze the precise conditions under which the underlying Gassmann relationship is valid for various inclusion‐based models. The results reveal the following: (1) Noninteracting effective medium theories are always consistent with the Gassmann prediction, simply because the elastic interactions are ignored. (2) The elastic interactions between randomly distributed pores cause heterogeneous pore pressure that violates the essential requirement of the Gassmann theory. The differential effective medium and self‐consistent approximation theories corresponding to this model thus are inconsistent with the Gassmann prediction. (3) The elastic interactions between periodically distributed pores cause uniform pore pressure; therefore, the Gassmann condition is fully satisfied. The T‐matrix approach explicitly takes into account such elastic interactions and thus is consistent with the Gassmann theory. It is interesting to notice that on top of other well‐known common types of heterogeneities, like pore structure or fluid heterogeneities, the distribution of pores and its associated elastic interactions can be a separate source of heterogeneity, and this makes Gassmann equations not valid anymore. Key Points: The essential conditions and physics for various inclusion‐based EMT to be consistent with the Gassmann theory are analyzedThe inconsistency of DEM and SCA with the Gassmann theory is mainly attributed to the random distribution of poresThe consistency of T‐matrix with the Gassmann theory is mainly attributed to the periodic distribution of pores [ABSTRACT FROM AUTHOR]