Source-reservoir-oil characteristics and evolution model of Chang 7 shale in Ordos Basin

Based on hydrocarbon generation simulation experiments, this study investigates oil generation, storage, and discharge, as well as the thermal evolution characteristics of the Chang 7 mudstone in the Ordos Basin. Through the integration of high-pressure mercury injection, liquid nitrogen adsorption, nuclear magnetic resonance, and other testing methods, the generated crude oil and its mobility was discussed, culminating in the establishment of a comprehensive evolution model for the oil . The findings indicate that the peak oil generation of Chang 7 mud shale occurs near a maturity level of Ro = 1. 0%, corresponding to approximately 120 mg / g TOC. Subsequently, as maturity increases, the quantity of liquid hydrocarbons gradually decrease while gaseous hydrocarbons show a gradual increase. The cumulative hydrocarbon generation continues to rise. The discharge of liquid hydrocarbons reaches its maximum (about 64. 55 mg / g TOC) at a Ro of 1. 15%. As maturity further increases, the discharge rate of liquid hydrocarbons decreases rapidly. With the increase of thermal evolution degree, the micropore volume of Chang 7 mud shale continues to increase, while the mesopore volume initially increases and then decreases. The macropore volume exhibits an initial decrease followed by an increase. The movable fluid saturation experiences an initial increase, followed by a decrease, and then another increase with increasing thermal maturity. On average, the movable fluid content in mudstone with varying maturity levels is 23. 17%. Based on the data pertaining to hydrocarbon generation, expulsion, retention, pore evolution, and movable fluid, the evolution process of Chang 7 mudstone can be divided into four stages: low maturity, mature self-saturation, mature drainage, and mature-high maturity. © 2024 University of Petroleum, China. All rights reserved.