Experimental Study of Shale Pore Structure Sensitivity to External Fluids in Jiyang Depression in China

The pore structure of shale in the Jiyang Depression is influenced by acid and alkali solutions, and is related to the saturated fluid stage. Revealing the characteristics of external fluid influence on the pore structure of the Jiyang Depression is of great significance for the optimization of shale fracturing fluids and the study of microscale mechanisms to enhance oil recovery in the Jiyang Depression. In this paper, first, microscale pore nuclear magnetic resonance experiments were conducted on shale rock cores before and after the action of fracturing gel breaking fluid, acid solution, and alkaline solution under reservoir temperature and pressure conditions. Then, the influence of external fluid on pore structure under different pore size conditions was analyzed. Finally, a comparative analysis was conducted on the sensitivity of external fluids to porosity and porosity ratio under different pore size conditions. Results show that: (1) the effect of fracturing gel breaking fluid on the total porosity of shale is relatively small. (2) As the acid mass fraction increases, the signal intensity corresponding to the microscale pores in the core increases. (3) The impact of external alkaline fluids on the total porosity of shale is mainly damage. Because clay minerals are sensitive to external fluids, the reservoir is external to foreign fluids.