Study On The Model Of Fluid Flow In HEGF Fracture Network For Horizontal Well In Shale Gas Reservoir

High energy gas fracturing(HEGF) technology can overcome the restrict of water resources to provide support for the development of shale gas in China. According to the characteristics of reservoir matrix in which the nano-pores distribute widely, the features of fracture of HEGF, the exist of adsorbed gas, and the complexity of gas flow patterns, in this paper, first, the formula of adsorption thickness is deduced from Langmuir isothermal adsorption equation, Polanyi adsorption theory, or FHH adsorption theory; second, the critical pore diameter which divides the flow pattern is expressed by Knudsen number; third, the apparent permeability in matrix is derived based on the physical meaning of mass flux considering the coexistence of various flow patterns; last but not least, the model of fluid flow in HEGF fracture network for horizontal well in shale gas reservoir is obtained by correct that the item of gas desorption is added in seepage differential equations. After solving and parameters analysis, the main conclusions are obtained as follows:(1) The thickness of adsorbed gas increases with the pressure growing and gradually stabilizes. The three adsorption thickness calculation methods have different applicability;(2) The critical pore diameter that divide the flow patterns of gas is not affected by temperature. As the pressure is small, the critical pore diameter decreases rapidly with the increase of pressure. When the pressure increases to more than 25 MPa, the value tends to be stable;(3) The apparent permeability decreases with the increase of pressure, and consider the case of adsorption, the value is relatively smaller. At the reservoir pressure, the reduction of apparent permeability considering the adsorption is about 13%; in addition, flow patterns have great influence on the apparent permeability. The apparent permeability of single Fick diffusion has 2 orders of magnitude smaller than single slippage apparent permeability;(4) According to the analysis of the influence factors of shale gas production: ① In the constant production condition, the higher the permeability of matrix and fracture is, or the longer and wider the vertical fracture is, the required production pressure is smaller; ② The greater the Langmuir volume is and the higher the Langmuir pressure is, the reservoir pressure declines more slowly; ③ The pressure drops more slowly for the reservoir with larger proportion of artificial fracturing length or larger shape factor in the constant production condition; ④ The producing pressure of shale gas wells has nonlinear negative correlation with fracture permeability and artificial fracturing length ratio, so the fracture with too high permeability or SRV which is too large are not desirable.