Mechanical Properties and Fracture Propagation in Shale with Different Types of Mineral Cementation: A Case Study of the Longmaxi Formation

During the extraction of shale oil from the Longmaxi Formation in the Sichuan Basin, it is found that the core samples contain natural fractures cemented by various minerals. However, the core extraction process is complex and expensive. In order to further investigate how cracks propagate and initiate in samples containing cementing layers under compression conditions, this study developed an experimental method involving plug cutting and mineral cementation reconstruction for the preparation of representative semi-artificial core samples. Through comprehensive analysis using computed tomography (CT), stereomicroscopy, and mechanical testing, we have demonstrated a high degree of consistency between artificial cemented cracks and natural cemented cracks. Through triaxial compression and Brazilian splitting experiments on artificially cemented samples, we found that low and high confining pressures significantly affect crack morphology. By using Abaqus finite element simulation to add crack propagation modes during the compression process of cement layers, we showed that different mineral cements (quartz, clay, and calcite) have secondary effects on crack morphology on the basis of confining pressure.