科研之友
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摘要
As the development of unconventional gas resources has progressed, the heterogeneity and complexity of shales as gas and oil reservoirs have become apparent. The production histories from shales. both within a sequence of interbedded strata and from adjacent wells, commonly exhibit inexplicable variations and predictions from numerical modeling are rarely accurate. As a result of the variability in the reservoir and rock parameters of gas shales, the complex interaction between the shale properties and the producibility of the reservoir is seldom apparent One of the most difficult parameters to quantify is the fabric. This study compares the relative importance of the fabric parameters of gas shales on their producibility using a commercial numerical simulator and field and laboratory determined rock properties. The fabric parameters include the stress-dependent fracture permeability, which controls the gas transport through the fracture network, as well as the effective fracture spacing, which controls the path length for gas transport through the matrix, and the stress-dependent matrix permeability, which controls the gas transport through the matrix. The results of the numerical simulations show that for a wide range of stress-dependent fracture permeabilities, stress-dependent matrix permeabilities, and fracture spacings, the productivity of a gas shale reservoir is limited by inefficient gas transport through the matrix. The matrix permeability below which gas production is subeconomic is not a specific value, but varies with the effective fracture spacing and with fracture permeability. The matrix permeability and effective fracture spacing have a greater impact on the producibility of strata with larger fracture permeabilities. The influence of the effective fracture spacing on production is greater than the influence of the matrix permeability. The lower production associated with a large fracture spacing (or a small matrix permeability) can be offset by a large matrix permeability (or a small fracture spacing). The production simulations also show the strong dependence on the geomechanical properties of the rock, which affect how the gas transport through the matrix and fractures changes with stress. The influence of the geomechanical properties on the producibility depends on whether the production is limited by the gas transport through the matrix. When the fabric parameters result in a matrix-independent production (small fracture spacing, large matrix permeability, small fracture permeability), the production is solely controlled by the stress-dependent fracture permeability, with larger initial fracture permeability, larger Young's modulus, and larger Poisson's ratio resulting in higher production. In this case, Young's modulus is much more influential than the Poisson's ratio. When the fabric parameters result in a matrix-limited production, the rock mechanics parameter a, which relates the exponential decline of matrix permeability with effective stress, has the strongest influence on the producibility. The influence of Poisson's ratio on producibility not only varies with the fabric parameters, but also with the Young's modulus and a. When the production is matrix-limited, a smaller Poisson's ratio results in a higher production for all cases except when both a and Young's modulus are small.
- 出版日期2012-12-1
