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| Study on meso-damage mechanism of shale reservoir rock based on digital cores |
| LI Jing1，LIU Chen1，LIU Huimin2，WANG Jiandong2，ZENG Zhiping3，XIE Yetong1 |
| (1. School of Pipeline and Civil Engineering，China University of Petroleum，Qingdao，Shandong 266580，China；2. Manage Center of Oil and Gas Exploration of SINOPEC Shengli Oilfield Company，Dongying，Shandong 257017，China；3. Research Institute of Exploration and Development，Shengli Oilfield，SINOPEC，Dongying，Shandong 257015，China) |
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Abstract Rock damage has a significant impact on the mechanical properties and seepage characteristics of reservoirs. In order to study the meso-damage mechanism of reservoir shale，CT scanning test was carried out to reconstruct three-dimensional digital cores. Subsequently，rock mechanical parameters were obtained based on the uniaxial compression test and the Brazilian test，and the uniaxial compression numerical simulation was carried out by using the rock plastic damage constitutive model. The results show that：(1) When the shale is compressed，the damage starts from the pore dense area，then the damage value increases，and finally the damage range expands until each damage area penetrates，forming shear oblique cracks. (2) There are different stress thresholds for the compression damage and the tensile damage. When the shale is compressed，the compressive stress first reaches the stress threshold of the compression damage and the compression damage occurs at once. The tensile damage，showing hysteresis，occurs where the compression damage is larger，and its damage volume is smaller than that of the compression damage. (3) The distribution range of the pore equivalent diameter of shale is 0–200 μm，and the pores with an equivalent diameter of 10–40 μm contribute the most to porosity. As the porosity increases，the decrease rate of the post-peak strength decreases and the ductility of the rock gradually increases. (4) The spatial distribution of pores has a great influence on the damage propagation form and the failure form of shale. Fractal dimension is introduced to characterize the complexity of the pore structure. The fractal dimension affects the peak strength of rock only when the porosity is large. Under the same porosity，the larger the fractal dimension，the lower the peak strength. The fractal dimension has little influence on the elastic modulus of rock. Both the porosity and the fractal dimension have a great influence on the damage volume of rock. The larger the porosity and the fractal dimension，the larger the damage volume.
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2022, Vol. 41 
