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以往的研究资料表明应力差对裂缝高度的控制占主导地位,而杨氏模量差的影响则较小。然而,最近一项研究表明模量差对裂缝的几何尺寸和支撑剂的铺置有非常重要的影响。进一步研究,我们考虑模量差和就地应力差对裂缝几何尺寸的联合影响。研究中应用了模量精确分层的拟三维水力压裂模拟器。在相同地应力差的条件下,将平均模量和分层模量计算的裂缝高度进行了比较。基于基本的断裂力学理论和水力压裂中流体压力的耦合作用,对结果进行了分析和解释。其中一个重要发现是低模量的地层也能够控制裂缝高度。研究中得出的结论可应用于中等模量差到较大模量差地层的水力压裂施工。研究的机理也可以部分地解释一些从微地震和测斜仪成像得出的最新结论。这些结论显示了实际裂缝高度小于普通应用拟三维水力压裂模拟器(基于平均模量)预测的裂缝高度。
Previous research data show that the control of the crack height is dominated by the stress difference, while the influence of the Young’s modulus difference is smaller. However, a recent study shows that the modulus difference has a very important influence on the fracture geometry and proppant placement. For further study, we consider the combined effect of modulus difference and in-situ stress difference on fracture geometry. In this study, a quasi-3D hydraulic fracturing simulator with accurate modulus stratification was applied. Under the same condition of stress difference, the crack height calculated by average modulus and stratified modulus was compared. Based on the basic theory of fracture mechanics and the coupling of fluid pressure in hydraulic fracturing, the results are analyzed and explained. One of the key findings is that low modulus formations can also control fracture height. The conclusion reached in the study can be applied to the hydraulic fracturing of poor strata with medium modulus and relatively large modulus. The mechanics of the study may also partly explain some of the latest findings from microseismic and inclinometer imaging. These conclusions show that the actual fracture height is less than the fracture height predicted by the conventional three-dimensional hydraulic fracturing simulator (based on the average modulus).