Coplanar perforation is a new perforation technology with unique perforation position that can improve the efficiency of hydraulic fracturing of horizontal wells in low permeability reservoirs which have low porosity, low permeability and are difficult to explore. So it is important to know how fractures initiate and propagate as well as the optimal perforation parameters. A large-scale true tri-axial hydraulic fracturing simulation experiment is conducted to study fracture initiation characteristic and propagation pattern of coplanar perforation in horizontal wells under different in-situ stresses, compared with conventional helix perforation in horizontal wells under the same in-situ stresses. In the meantime, the three-dimensional finite element method is used to study the influences of different perforation parameter combinations set according to field data on fracturing pressure in horizontal wells, including shot length, shot diameter and shot density. The experiment results show that the coplanar perforation has simpler fracture propagation pattern under higher stress difference and has following advantages compared to conventional helix perforation: (1) reducing the fracturing pressure, (2) controlling the fracture propagation to reduce the complexity of near-wellbore fracture and (3) reducing the near-wellbore friction resistance. The numerical simulation results show that: (1) the fracturing pressure does not decrease linearly as the shot density increases, it falls rapidly when the shot density increases from 9 to 15 holes per meter, but when the shot density increases from 15 to 21 holes per meter, it falls slowly and finally remains almost constant, (2) the fracturing pressure decreases as the shot diameter increases, and (3) the fracturing pressure stays the same as the shot length increases. Through the conclusions of experimental and numerical simulation, we could provide some valuable suggestions to the hydraulic fracturing on filed. During hydraulic fracturing process in low permeability reservoirs, coplanar perforation technology with high shot density (21 holes/m) and large shot diameter (0.03m) should be used. The experimental and numerical simulation conducted in this paper show a real process of hydraulic fracturing with coplanar perforation. The advantages and optimal perforation parameters of coplanar perforation are proposed to give guidances for hydraulic fracturing on field.
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