Numerical Simulation of Hydraulic Fracturing Process of Shale in Jiyang Depression Layer

Abstract

ABSTRACT As an important unconventional energy source, shale oil is widely distributed and has huge reserves, which is one of the alternative energy sources in the future. In this paper, the shale reservoir of the grain-bearing layer of Well A in the Jiyang Depression in the Bohai Bay Basin was used as the research object to carry out the numerical simulation of hydraulic fracture. Firstly, the 3D geological model of shale oil reservoir is simplified, the spatial distribution of reservoir fracturing fractures and textured shale is described, and the 3D geometric model of the reservoir is established by ABAQUS. Secondly, based on the stress balance equation and fluid continuity equation, traction separation criterion and flow equation of cohesion unit, a coupled numerical model of reservoir stress-seepage flow is established. Then, using on-site production and original in-situ stress as the loading conditions, the required parameters are input into the model, and the finite element method is used to solve the model. It is found that the simulated fracture morphology is similar to the actual single hydraulic fracture morphology, the pressure accumulation is mainly concentrated in the reservoir, and the Mises stress at the water injection point reaches a maximum at the beginning of injection, and the stress gradually decreases as the fracturing progresses. The pore pressure in the reservoir is mainly distributed near textured shale reservoirs and fractures, and the pore pressure near the fractures can reach more than 10MPa. The width reaches a stable value after cracking, indicating that hydraulic fracturing can effectively control fracture spread and produce a relatively stable fracture structure. INTRODUCTION The Jiyang depression in the Bohai Bay Basin is rich in shale oil resources, with a resource volume of 4.1 billion tons. The shale in the Jiyang Basin is characterized by low evolution, deep burial, large shale thickness, and abnormally high temperature and high pressure. The shale structure is so dense that there are almost no cracks in the cores taken from deep underground, but there are obvious lamellar structures. Lamellar shale bedding developed a lot, the height of the development of bedding joints, bedding joints in the state of unfilled or semi-filled, with high seepage capacity. The lamellar facies has the characteristics of high porosity, large pore diameter, and good connectivity. According to the oil testing results, the shale facies with the most industrial oil flow are shale laminar argillaceous limestone and limestone argillaceous mudstone intercalated with thin sandstone or carbonate rock.