Self-adaptive rock physics modeling method for tight sandstone reservoirs
ZHANG Jinqiang1,2,3, LIU Zhenfeng1,2,3, LIU Xiwu1,2,3, Han Lei1,2,3
1. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 102206, China; 2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 102206, China; 3. State Energy Center for Shale Oil Research and Development, SINOPEC, Beijing 102206, China
Abstract:In traditional rock physics modeling, the mi-neral components are known, and the equivalent elastic modulus of the rock matrix is solved with the Voigt-Reuss-Hill model. In the practice of rock physics modeling for tight sandstone reservoirs, accurate mineral component interpretation cannot be provided due to incomplete logging data. As a result, the accuracy of conventional rock physics modeling is affected. To tackle the problem, we propose a self-adaptive method for the rock physics modeling of tight sandstone reservoirs. The me-thod uses both the Gassmann equation and the criti-cal porosity model to estimate the elastic modulus of the rock matrix. According to the interpreted shale content curves, the upper and lower bounds of elastic moduli of shale and sandy components are estimated with the least square method and Voigt and Reuss models. A simulated annealing algorithm is employed to find the approximate elastic moduli of shale and sandy components. The values are fine-tuned according to the principle of constant P-wave modulus, and finally, the reasonable para-meters for rock physics modeling are obtained. Area M in the southern Ordos Basin is subject to rock physics modeling with this method and the results show that the elastic parameters of shale and tight sandstone can be well distinguished. Shale is cha-racterized by a high P-wave/S-wave velocity ratio and a low P-wave velocity. For sandstone, the P-wave/S-wave velocity ratio and the P-wave velocity decline as the porosity increases.
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