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A Poromechanical Model of Hydraulic Fracturing Volumetric Opening
Engineering Fracture Mechanics ( IF 5.4 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.engfracmech.2020.107172
Li Wang , Hongzheng Xu , Yunxing Cao , Shimin Liu

Abstract In the present study, the hydraulic fracturing volumetric opening is referred to the volumetric opening in per unit bulk volume of rocks, in fact, the increment of porosity due to hydraulic fracturing, including the pore volumetric opening and fracture volumetric opening. The former is an idealized representation of elastic volumetric opening of widely distributed microcracks, fissures, and pores due to porous flow, and the latter is the volumetric opening of newly generated trunk fracture due to breakdown of rock skeleton. The poromechanical model is a set of mechanical formulas to model the evolutions of these volumetric openings in a hydraulic fracturing process, so that to give a proper evaluation of hydraulic fracturing openings in RVE scale. Firstly, a three-staged hydraulic fracturing process is proposed, based on which, staged expressions of volumetric openings are established using the theory of poroelasticity and the damage model of cohesive breakdown. Then, the precise evolutions of these volumetric openings are obtained by incorporating hydraulic fracturing propagation regimes into those expressions aforementioned. Therefore, the poromechanical model proposed in the present study is bridging the gaps between the two classic theories, the poroelasticity and hydraulic fracture in a RVE scale. As examples, four limiting cases of hydraulic fracturing are chosen to show how to use this model to calculate the hydraulic volumetric openings. These limiting cases are corresponding to the four limiting propagation regimes of hydraulic fracturing, the storage-viscosity regime, leak-off-viscosity regime, storage-toughness regime, and leak-off-toughness regime.

中文翻译:

水力压裂体积开孔的力学模型

摘要 目前研究中的水力压裂体积开度是指单位体积体积岩石中的体积开度,实际上是水力压裂引起的孔隙度增量,包括孔隙体积开度和裂缝体积开度。前者是广泛分布的微裂缝、裂隙和孔隙因多孔流动而弹性体积张开的理想化表示,后者是由于岩石骨架破裂而新产生的主干裂缝的体积张开。孔隙力学模型是一组力学公式,用于模拟水力压裂过程中这些体积开口的演变,以便在 RVE 尺度上对水力压裂开口进行正确评估。首先提出了三级水力压裂工艺,在此基础上,使用多孔弹性理论和内聚破坏损伤模型建立了体积开口的阶段表达式。然后,通过将水力压裂传播机制纳入上述表达式中,获得这些体积开口的精确演变。因此,本研究中提出的多孔力学模型弥合了 RVE 尺度中孔隙弹性和水力压裂这两个经典理论之间的差距。例如,选择了四个水力压裂的极限情况来展示如何使用该模型来计算水力体积开口。这些极限情况对应于水力压裂的四个极限扩展状态,即储存粘性状态、泄漏粘性状态、存储韧性状态和泄漏粘性状态。
更新日期:2020-08-01
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