Semi-analytical modeling of transient pressure behaviour for a multifractured horizontal well in a gas reservoir with a complex fracture network by considering effects of slippage, stress-sensitivity, and gas adsorption/desorption

Abstract

A semi-analytical technique has been developed, validated, and applied to quantify the pressure behaviour of a multifractured horizontal well (MFHW) in a gas reservoir with discrete fracture networks and an arbitrary boundary. Considering stress-sensitivity and the slippage effect in the matrix subsystem, a pseudo-pressure is incorporated into the gas flow equations. To weaken the strong nonlinearity from such a combined effect, the dual-reciprocity boundary element method (DRBEM) is applied to efficiently and effectively linearize the governing equations by replacing the nonlinear function with a series of particular solutions. Comparing with the boundary element method (BEM), not only can the DRBEM be used to obtain the accurate solution in any space and time domains, but also it is flexible to deal with the nonlinearity restriction in the governing equations. The finite volume method (FVM) is then adopted to simulate gas flow behaviour in the fracture subsystem with different fracture geometries. Not only can the proposed model be applied to a complex fracture network and operating schedules, but also capture complex gas flow behaviour including the Langmuir sorption, slippage effect, and stress-sensitive effect in a gas reservoir with a discrete fracture network and an arbitrary boundary. The mathematical formulations have been validated and then extended to field applications. A strong stress-sensitive effect is found to result in a large pressure drop and offset the permeability-enhancing effect from the slippage effect. In addition, a decrease in pressure drop derived from gas desorption would restrict the stress-sensitive effect. Furthermore, it can be found that each individual factor imposes a significant impact on the linear flow and boundary dominated flow regimes. On the basis of a mutual interference, the combined effect (i.e., stress-sensitivity, slippage effect, and gas adsorption/desorption) may be weaker than that of each individual factor. In the late boundary-dominated flow regime, the effect of boundary shape becomes more obvious on the pressure distribution curves since the pressure wave would reach the boundaries near fractures within a relatively short time.