Meitan kexue jishu (Sep 2023)
Simulation investigation on spatial deflection of multiples fractures of multistage perforation clusters in hydraulic fracturing
Abstract
The morphology of complex fracture network in hydraulic fracturing engineering in deep tight oil and gas reservoir is a crucial factor affecting oil and gas recovery, and it is necessary to accurately evaluate and optimize the fracture propagation behavior. Multistage fracturing of horizontal wells with multiple perforation clusters involves thermal diffusion, fluid flow and deformation of rock matrix between the reservoir and fluid in pores and fractures. Thermal diffusion effect and multi-physical field coupling are typical characteristics of fracturing in deep tight rock reservoirs. At the same time, the propagation of fracture network is related to the disturbance between adjacent fractures. The perforation clusters spacing and initiation sequence in fracturing process will lead to different degrees of unstable propagation of parallel fractures. It is of great significance to understand the influence mechanisms of internal and external factors for the effective evaluation of fracture networks, such as the coupling of multiple physical fields and fractures disturbance. The thermal-fluid-solid coupling effect in deep reservoir was considered comprehensively to investigate the stress shadow effect and the disturbance deflection behaviors of multiple fractures in three-dimensional (3D) propagation process of hydraulic fracture network. 3D engineering scale numerical model for multistage fracturing in horizontal wells was established. The influence of thermal diffusion effect on 3D fracture, and the propagation disturbance behaviors of 3D fracture network under different perforation cluster spaces and different fracturing scenarios (sequential, simultaneous and alternate fracturing) were analyzed in typical engineering conditions. The results shown that, the stress disturbance region caused by fracture propagation in deep tight oil and gas reservoirs had superposition and overlaying behaviors in multiple fractures, forming a stress shadow effect and spatial deflection of fractures. The decrease of space between multiple perforation clusters in horizontal wells would increase the stress shadow areas and aggravate the mutual interaction between fractures. Compared with the sequential fracturing of multiple perforation clusters, the simultaneous fracturing would increase the stress shadow areas, and the alternate fracturing may conversely reduce the stress shadow areas to alleviate 3D propagation disturbance of fracture network to form an effective scheme for optimizing the spatial morphology of fracturing fracture network. The heat transfers between the fracturing fluid and the rock matrix in deep tight rock reservoirs, and the fracture propagation area and volume under each fracturing scheme were significantly enhanced, indicating that the thermal effect promoted fracture propagation and became an important factor affecting the fracture propagation.
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