Fracturing Simulation and Design Optimization of Fracture Network in Non-Uniform Stress Field of Deep Shale Gas

Abstract

Abstract The deep shale is influenced by multiple tectonic movements, resulting in well-developed reservoir faults and a non-uniform distribution of the stress field near the wellbore. The volume of the fracture network may be impacted by non-planar, asymmetric, and irregular behavior during hydraulic fracturing. One important aspect influencing gas well productivity is the volume of the fracture network. In the complex structure of deep shale gas reservoirs, a model is established in this study to define the non-uniform stress field near faults and to predict the propagation of fracture network. By contrasting the models with microseismic monitoring data from the mining field, the models' dependability is confirmed. The impact of fault type, fault offset, length, height, strike, dip, and distance on the fracture network volume is quantitatively investigated, and the influence of fault characteristic parameters on the stress field is quantitatively calculated. The ideal stimulated reservoir volume (SRV) is the design objective for hydraulic fracturing inter-cluster spacing, which is optimized based on the fault characteristics of the Y101 well area in southern Sichuan. The findings indicate that the stress field rotates clockwise near reverse faults and right-lateral strike-slip faults, and counterclockwise near normal faults and left-lateral strike-slip faults. A bigger fracture network volume results from the small stress difference near normal faults and right-lateral strike-slip faults, whereas a smaller fracture network volume results from the significant stress difference near reverse faults and left-lateral strike-slip faults. The following is a ranking of the fault structural parameters that have an impact on the volume of the fracture network: dip > strike > displacement > distance > height > length. In the case of I fault, the ideal distance between clusters is smaller the closer to the fault the larger the horizontal stress difference, which prevents the fracture network from propagating. When the strike angle for Grade II, III, and IV faults is less than 50°, the closer the fault is to the fault, the larger the horizontal stress differential. This does not promote the fracture network's growth, and it also results in a smaller ideal spacing between clusters. When the strike is more than 50°, the ideal distance between clusters of perforations is bigger and the horizontal stress difference is less the closer the strike is to the fault, which promotes the propagation of the fracture network. Horizontal wells have to be positioned appropriately away from faults; a distance of more than 2000–4000 meters is recommended for level I faults, more than 1500–2500 meters for level II faults, more than 700–1200 meters for level III faults, and a closer distance is permissible for level IV faults.