APPARENT PERMEABILITY FOR SHALE GAS CONSIDERING ADSORPTION AND FLOW PATTERNS: TAKING THE LONGMAXI SHALE GAS RESERVOIR OF SICHUAN BASIN AS AN INSTANCE

The flow pattern is unique in a certain range of pore size divided by the Knudsen number. In order to characterize permeability of nano-pore in shale gas reservoir more accurately, and solve the issue of apparent permeability calculation, the formulas of nano-pore permeability are put forward considering the influence of adsorption gas and pore size distribution, taking the chang7 shale gas reservoir of of Ordos Basin as an instance. After the calculated results were compared and analyzed, the conclusions are obtained as follows: (1) Pore size is the main factor to determine the flow pattern; (2) There are three main flow pattern in the shale reservoirs nano-pore, slip flow, Fick diffusion and transition diffusion, meanwhile Darcy percolation and Knudsen diffusion do not exist; (3) Flow pattern has great influence on apparent permeability and adsorption has a greater impact in a high pressure condition (greater than 20 MPa).