Thermal fracturing in reservoir rocks can cause significant increase in permeability. The change in permeability due to fracturing was predicted using the change in elastic wave velocity, density, and elastic moduli. Westerly granite samples were thermally treated to 250, 450, 650 and 850 °C. Increasing the temperature produces an increase in fracture length, aperture and density that is isotropically distributed. The permeability was measured at 10, 30 and 50 MPa effective pressure using deionized water as the pore fluid. The permeability was correlated to P- and S-wave velocities, bulk density, and static bulk modulus that were measured at similar effective pressures on the same suite of samples. Kachanov’s (Elastic solids with many cracks and related problems, in: John, Theodore (eds) Advances in applied mechanics, Elsevier, pp 259–445, 1994) model was used to calculate the evolution of fracture density. Closure of fracture, due to increasing effective pressure, caused the permeability and fracture density to decrease, and the other parameters to increase. Thermal treatment caused a systematic increase in permeability and fracture density, and a decrease in the other parameters. Empirical relationships with high correlation coefficient exist between permeability and the other parameters for both dry and saturated conditions, which vary with effective pressure. Overall, we conclude that the elastic wave velocity, density and bulk modulus can be used to predict the change in permeability due to isotropic fracturing. However, a reliable method would be required to upscale these laboratory measurements for modelling and describing the permeability within a granitic reservoir.

中文翻译：

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使用速度、密度和体积模量预测微裂缝岩石的渗透率演变

储层岩石中的热压裂可导致渗透率显着增加。使用弹性波速度、密度和弹性模量的变化来预测由于压裂引起的渗透率变化。西风花岗岩样品经过热处理至 250、450、650 和 850 °C。提高温度会导致各向同性分布的裂缝长度、孔径和密度增加。使用去离子水作为孔隙流体，在 10、30 和 50 MPa 有效压力下测量渗透率。渗透率与 P 波和 S 波速度、体积密度和静态体积模量相关，这些是在相同的一组样品上在类似的有效压力下测量的。Kachanov 的（具有许多裂纹和相关问题的弹性固体，在：John, Theodore（编辑）应用力学进展，Elsevier，第 259–445 页，1994）模型用于计算裂缝密度的演变。裂缝闭合，由于有效压力增加，导致渗透率和裂缝密度降低，其他参数增加。热处理导致渗透率和裂缝密度的系统性增加，以及其他参数的降低。在干燥和饱和条件下，渗透率与其他参数之间存在具有高相关系数的经验关系，这些参数随有效压力而变化。总的来说，我们得出结论，弹性波速度、密度和体积模量可用于预测各向同性压裂引起的渗透率变化。然而，需要一种可靠的方法来提升这些实验室测量值，以模拟和描述花岗岩储层内的渗透率。