Abstract
Fracturing technology is an effective measure to exploit shale gas and the fractures improve the seepage ability of shale reservoir after fracturing. In this paper, taking Chang 7 of Yanchang Formation as the study area, a double porosity seepage model considering natural fracture was established and it was solved by finite element method of COMSOL5.5; then, shale gas seepage was analyzed under different angles between hydraulic fracture and natural fracture finally. Meanwhile, angles between hydraulic fracture and natural fracture were optimized by analyzing both the reservoir pressure distribution and bottom hole flowing pressure. Also, a permeability experiment with liquid was conducted to verify the accuracy of the numerical simulation result. Both numerical simulation and permeability measurement experiment get a uniform result that the optimal angle between hydraulic fracture and natural fracture is 90°. Permeability is the highest, shale gas seepage rate is the fastest, bottom hole flowing pressure is the highest, and also it is beneficial to the desorption of adsorbed gas in the matrix system and then effectively supplements reservoir pressure and bottom hole flowing pressure. The research results will provide some theoretical guidance for fracturing design.
Highlights
As one of the vital unconventional reservoirs, low porosity and very low permeability of shale reservoir make the development more difficult by traditional development method
It can be explained that free shale gas in fracture system makes a major contribution at the beginning of shale gas extraction with fixed production rate, gas migrates through a highly conductive fracture system, and different angles between hydraulic fracture and natural fracture have no interference with shale gas seepage
(2) Based on the established double porosity model, the seepage law and migration mechanism were studied by comparing the reservoir pressure and bottom hole flowing pressure of six types of angles between hydraulic fracture and natural fracture (15°, 30°, 45°, 60°, 75°, and 90°) through numerical simulation
Summary
As one of the vital unconventional reservoirs, low porosity and very low permeability of shale reservoir make the development more difficult by traditional development method. Some research results show that horizontal well and fracturing technologies are effective measures to improve single well productivity of shale gas [1,2,3]. In order to enable fractures to communicate with the reservoir effectively, it is necessary for the development of a low permeability oilfield to optimize the orientation of hydraulic fractures [4, 5]. Erefore, scholars have made the following research on the optimization of hydraulic fracture orientation. In order to research the influence of fracture orientation on productivity, Lemon et al [6] studied whether or not fracture orientation can improve the productivity of fractured well based on single-phase two-dimensional reservoir simulator technology.
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