Study on numerical well test method of gas reservoirs with large-scale fractures

Fractured gas reservoir has very strong heterogeneity when natural fractures with different scale exist. The traditional Dual Porosity Model and its extended models can't explain precisely about the effect of the fracture factors on the well-test curve, because these models are too idealistic for the gas reservoir. Thus, the paper presents a discrete fracture network model for gas reservoirs which contain large-scale fractures based on Monte Carlo random fractures method and Voronoi Non-Structural grid method, then founds math model of reservoir by Controlling Volume Finite difference method, and uses the fully implicit method for solving problems. Finally, after proving the well test curve of discrete fracture network model by the real well test curve of fractured reservoir, the well-test curve effected by large-scale fracture parameters (including numbers, angles, length) are discussed. The research results suggest that: the late pressure derivative curve is affected by the fracture characteristic parameters; the more number of fractures is, the greater decline of late pressure derivative curve; the longer of the length of fracture is, the earlier of late pressure derivative curve will appear, also the greater decline of late pressure derivative curve; the angle of fracture has little effect on the late pressure derivative curve, but when the fractures' angle is basically the same with the well radial grid direction, the pressure derivative curve decreased the earliest and had the biggest drop.