Abstract：Formation pressure affects the elasticity of shale reservoirs, and in deep high-pressure conditions, fracture structure is an important factor influencing the elasticity of shale reservoirs. At present, few seismic rock physical modeling methods for deep shale reservoirs consider the influence of pressure. Firstly, based on Toksöz inclusion theory, this paper considers the influence of effective pressure on the aspect ratio of cracks, establishes a quantitative relationship between effective pressure and the aspect ratio of cracks, and introduces the influence of effective pressure into the Eshelby Cheng model for pressure correction. Secondly, the corrected Eshelby Cheng model is em-ployed to couple the horizontal fractures affected by effective pressure into the background medium in the form of inclusions and build a seismic rock physics model of deep shale reservoirs considering pressure effects. Finally, the built seismic rock physics model is applied to the actual work area and compared with the non-pressure corrected Eshelby-Cheng model for estimating the P-wave and S-wave velocities. By analyzing the effects of effective pressure on the aspect ratio of fractures, Thomsen anisotropy parameters, and P-wave and S-wave velocities in the reservoir, the results show that in the early stages of effective pressure changes, the aspect ratio of fractures and Thomsen anisotropy parameters decrease with the increasing effective pressure. The P-wave and S-wave velocities of reservoirs increase with the rising effective pressure, and when the effective pressure increases to a certain limit, all three of the above tend to stabilize, which means that changes in effective pressure no longer affect the reservoir. The P-wave velocity and S-wave velocity prediction in deep shale reservoirs through this method is highly consistent with actual data, thus proving the applicability of this model for deep shale reservoirs.
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WU Chenyue, YIN Xingyao, YIN Linjie, LI Kun. Rock physical modelling for deep shale reservoirs involving the influence of pressure. Oil Geophysical Prospecting, 2023, 58(4): 893-901.
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