In the context of various oil - and - gas (O&G) problems, hydraulic - fracture - modeling research continues to develop. A fully - coupled Finite - Element (FE) framework has been developed, which includes the Cohesive Zone Model (CZM) and the eXtended Finite - Element Method (XFEM). By comparing and validating the simulation results with the analytical solutions of four asymptotic modes of fracture propagation and carefully conducted multi - axial fracturing experiments, this framework is applicable to both conventional and unconventional fracturing problems, including three - dimensional multi - zone injection, Diagnostic Fracture Injection Tests (DFIT), and multi - stage hydraulic fracturing. Moreover, simulations of large - scale length and time have been achieved through high - performance, large - scale parallel computing systems, such as problems of Step - Rate Tests (SRT), Produced - Water Re - injection (PWRI), and Cuttings Re - injection (CRI) at the actual field scale.
At the same time, a two - dimensional Cohesive Zone Model (CZM) coupled with the Continuum Damage Mechanics (CDM) model has also been developed. It expresses the separation criterion according to the damage tensor in adjacent body elements, and the residual tensile strength and shear strength follow a linear softening law and are calibrated according to the published shale triaxial compression tests. Single - cohesive - zone experiments show that this model can simulate the hardening, softening, and failure processes during damage propagation and can predict the strength and stiffness under different states.
Taking the shale reservoir in the gravel - bearing interval of Well A in the Jiyang Depression of the Bohai Bay Basin as an example, a hydraulic - fracturing numerical simulation was carried out. First, the three - dimensional geological model was simplified, and a three - dimensional geometric model of the reservoir was established. Then, a stress - seepage - coupled numerical model was established based on relevant equations, and the field production data and original in - situ stress were used as loading conditions for solution. It was found that the simulated fracture morphology was similar to the actual one, the pressure accumulation was concentrated within the reservoir, the Mises stress at the water - injection point changed significantly, the pore - pressure distribution in the reservoir was in specific areas and could reach a relatively high value, and the fracture width reached a stable value after initiation, indicating that hydraulic fracturing can effectively control fracture propagation.
In conclusion, fracture modeling of oil - gas reservoirs has made remarkable progress in hydraulic - fracturing research. These models and methods provide strong technical support for the development and stimulation of oil - gas reservoirs, and continuous in - depth research and optimization are still required in the future to better serve the development of the energy field.