Micro-fracture propagation and numerical simulation of fracture propagation under thermal simulation experiment of organic-rich shale: Chang-7 source rock in Yanchang, Ordos Basin

Abstract

Organic-rich shale as a high-quality source rock which is usually deposited in a high-temperature and high-pressure environment, and its internal organic matter will gradually transform into hydrocarbon and be discharged from shale. However, shale has polar porosity and permeability, making it difficult for hydrocarbon to be discharged from the shale through the pore throat. The latest research suggests that due to the strong hydrocarbon generation potential of shale rich in organic matter, the pressure generated by hydrocarbon can cause micro-fracture in the shale, leading to the expulsion of hydrocarbon from the micro-fracture. Therefore, this article uses hydrocarbon generation simulation experiments and Comsol Multiphysics to analyze the mechanical characteristics and damage propagation of micro-fracture during shale hydrocarbon generation process. The results show that with the increase of temperature and fluid pressure, micro-fracture of different lengths have different initial fracture pressures, and during the diffusion of micro-fracture, the stress inside the shale matrix and micro-fracture exhibits different diffusion characteristics.