Xu Yang

Existing research rarely considers the rough surface morphology of natural fractures and the radial migration of particles within the fractures along with their plugging behavior simultaneously. This study innovatively establishes a radial wedge-shaped flow space model of rough fractures using numerical fracture surface synthesis techniques. The computational fluid dynamics-discrete element method was used to simulate the radial migration, bridging, and plugging processes of particles under different factors. The results show that the size of rock samples does not constrain the high-precision digital reconstruction method for fractures. It can be adjusted to the appropriate size according to research needs. In rough fractures, the radial migration of particles exhibits strong disorderliness, with high probabilities and intensities of particle collisions, making effective plugging rather challenging. In contrast, within flat wedge-shaped fractures, forming annular plugging zones at different locations for particles of varying sizes, thus achieving higher plugging efficiency. When drilling encounters high-angle or vertical fractures in straight wells, linear flow tends to occur. However, when encountering nearly horizontal fractures, radial flow prevails more often, causing significant disturbances between streamlines in local areas. Higher-viscosity fluids exhibit poorer mobility, which delays the timing of particle bridging and plugging. Additionally, the reduced fluid mobility lessens the disordered movement of particles within the fracture, thereby decreasing the intensity of particle collisions. Excessively low fluid pressure results in insufficient driving force for particle migration, thereby failing to plug the fractures effectively. This research provides new insights into the mechanisms of fluid loss during deep shale gas development and potential control strategies.

The Dengying Formation within Pengtan 1 well area in the Sichuan Basin is a vital gas reservoir for exploration and development. The reservoir is situated in a complex fault block structure characterized by multistage fault evolution, leading to a complicated distribution of tectonic fractures crucial for the accumulation and migration of oil and gas. This study establishes a geological model to describe the fault patterns observed in the region and conducts numerical simulations of the paleotectonic stress field. Moreover, we combine rock fracture criteria and strain and surface energy theories to predict tectonic fractures quantitatively. Our findings indicate that the tectonic fractures in the study area predominantly consist of shear fractures, with primary development of low‐angle and oblique fractures and, to a lesser extent, high‐angle fractures. These fractures generally exhibit trends in the north–northwest (NNW), northeast (NE), nearly east–west (EW), and nearly south–north (SN) directions. Most fractures formed during the Yanshanian–Himalayan period are identified as effective fractures. The maximum and minimum principal stress values recorded for the Himalayan period of tectonic activity were 150–180 and 120–150 MPa, respectively. Faults significantly influence the distribution of tectonic stress, and stress concentration usually occurs near the fault. A significant correlation exists between tectonic stress and burial depth, exhibiting lower stress levels at shallower depths. In addition, the linear density of fractures gradually decreases from the fault core to its periphery and further decreases to areas far away from the fault. In these three regions, fractures mainly develop in the order of high angle, oblique, and low angle. This study enhances our understanding of the fracture dynamics within the Dengying Formation, contributing valuable insights into the region’s geomechanical properties and potential hydrocarbon exploitation strategies.

The extent of fracture development is associated with the degree of enrichment of a natural gas reservoir and its productivity. Based on numerical simulation results of the paleotectonic stress field, a set of evaluation methods for determining the degree of development of reservoir tectonic fractures were established using rock rupture criteria. Taking the fourth member of the Leikoupo Formation in the Pengzhou area of western Sichuan as an example, a finite element (FE) method was employed to simulate the paleo-tectonic stress field during the period of fracture development, and the degree of tectonic fracture development was further evaluated using the above methods. The results indicated that effective fractures were created in the Himalayan period. In this time, mainly NE–NEE and nearly E–W strike tectonic fractures were developed in the target layer. The fractures were mainly low-angle and oblique fractures, while the high-angle fractures were less developed. According to the integrative fracture index (F), five typical fracture development areas were determined: the fault zone, and the northern, eastern, southeastern, and central regions of the study area. The reliability of the fracture prediction results was verified using fracture distribution statistics and gas production test results.