工程科学学报 (Nov 2020)
Control of fracturing behavior of fractured reservoir under horizontal wells
Abstract
There are many practical engineering problems in the hydraulic fracturing of crack reservoirs, such as the maintenance of wall rock, the efficiency of reservoir's permeability and the prevention of groundwater hazard. In this paper, the control mechanism of fracture pressure under multi-field and multi-phase coupling in horizontal wells and the fracturing evaluation of crack reservoirs were studied deeply to address these issues. Firstly, the transformation effect of the perforation concentration on the original stress field was analyzed. Secondly, the permeability of fracturing fluid in the primary fractures was considered. Finally, based on the strength principle of fracture mechanics, the calculation model of fracture pressure for horizontal wells in the reservoir was established. Furthermore, the influence of the spatial geometric parameters of the fracture field on the initiation pressure was analyzed, and the concept of the characteristic parameters of the fracture field was proposed. The results indicate that the coupling of fluid-solid multiphase in the fields of perforation stress, fracturing fluid permeation and original fracture leads to horizontal well hydraulic fracturing, and the characteristic parameter of fracture field plays a leading role in controlling the initiation pressure. Among them, the biggest controlling factor on initiation pressure is crack width. When the crack width of reservoir is within 200–700 μm, hydraulic fracturing has practical significance for improving reservoir permeability, which solves the problem about the quantification of initiation pressure and the fracturing evaluation in crack reservoirs. By calculating initiation pressure and contrasting to engineering example, it is found that the productivity of the sandstone reservoir is very ideal in the H8 section of the eastern Sulige gas field after hydraulic fracturing, and the theoretical value of fracture initiation pressure is in good agreement with the measured value, which verifies the correctness of the model. These can provide theoretical basis for fracturing construction of horizontal wells.
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