AN UNSTABLE POROUS FLOW MODEL OF MARINE-CONTINENTAL TRANSITIONAL SHALE GAS RESERVOIR

Marine-continent transitional shale is often interbedded with coal seams and sandstone. The reservoir has poor continuity, rapid lateral change, and high heterogeneity. Hydraulic fracturing technology is the key method to obtain economic production. However, there is currently a lack of effective unstable porous flow model of Marine-continent shale gas reservoirs. In response to this problem, considering the characteristics of shale gas adsorption/desorption, diffusion, fractures, and shale heterogeneity, a heterogeneous shale gas mathematical model was established and solved by using boundary element method. First, a vertically fractured well model in MCT shale-gas reservoir is built. Second, Radial composite model is used to reflect the high heterogeneity, and Langmuir isothermal adsorption curve is applied to describe the gas adsorption/desorption and diffusion. Dual-porosity model, boundary element model, and Pedrosa’s substitution are respectively used to simulate the natural fractures, hydraulic fractures, and effect of stress-sensitive permeability The analysis results show that the unstable flow characteristics in Marine-continent transitional shale gas reservoir include flow early stage, bilinear flow, linear flow, inner radial flow, shale gas desorption, transition section, outer radial flow and boundary-dominated flow stage. This model has been applied in the process of well testing of Marine and continental transitional shale gas in Ordos Basin, and the actual effect is good. The research results can provide some theoretical support for the fracturing evaluation of similar shale gas reservoirs, and it has a good application prospect.