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 引用本文: 孙可明, 张树翠. 含层理页岩气藏水力压裂裂纹扩展规律解析分析[J]. 力学学报, 2016, 48(5): 1229-1237.
Sun Keming, Zhang Shucui. HYDRAULIC FRACTURE PROPAGATION IN SHALE GAS BEDDING RESERVOIR ANALYTICAL ANALYSIS[J]. Chinese Journal of Theoretical and Applied Mechanics, 2016, 48(5): 1229-1237.
 Citation: Sun Keming, Zhang Shucui. HYDRAULIC FRACTURE PROPAGATION IN SHALE GAS BEDDING RESERVOIR ANALYTICAL ANALYSIS[J]. Chinese Journal of Theoretical and Applied Mechanics, 2016, 48(5): 1229-1237.

## HYDRAULIC FRACTURE PROPAGATION IN SHALE GAS BEDDING RESERVOIR ANALYTICAL ANALYSIS

• 摘要: 页岩气蕴藏在页岩层中，页岩层的层理性构造使其水力压裂裂纹扩展与常规均质储层不同.为研究页岩储层水力压裂的裂纹扩展规律，基于复变函数保角变换，得出裂纹尖端应力集中解，考虑页岩非均质、强度各向异性特点，通过比较裂纹沿各方向扩展所需的裂缝尖端水压力，推导出水力压裂裂纹垂直于最小地应力方向稳定扩展过程中在斜交层理后的扩展判据.分别定义了水力压裂裂纹在层理处起裂和沿层理扩展的弱层和岩石基体临界强度比，根据两个临界强度比确定水力压裂裂纹遇层理时在层理处起裂和沿层理扩展的层理弱面强度范围，以此表示水力压裂裂纹转向层理扩展的难易程度.通过对裂纹扩展判据的分析得出：层理起裂弱层和岩石基体临界强度比随层理走向线与第一主应力夹角和层理倾角的减小以及第三主应力和岩石基体强度的增大而增大；层理走向角小于35.26°时，层理起裂弱层和岩石基体临界强度比随第一主应力的减小以及第二主应力的增大而增大；反之，层理起裂弱层和岩石基体临界强度比随第一主应力的减小以及第二主应力的增大而减小；层理扩展弱层和岩石基体临界强度比随层理走向线与第一主应力夹角、层理倾角和地应力差的减小以及岩石基体抗拉强度的增大而增大.层理起裂条件与层理扩展条件同时满足时，水力压裂裂纹转向层理方向扩展.

Abstract: Shale gas deposits in shale reservoirs, whose bedding structures are different from conventional heterogeneous reservoirs. This also makes the shale reservoirs have different crack propagation laws in hydraulic fracturing. In order to investigate the crack propagation laws of shale reservoir hydraulic fracturing, complex variable function and conformal transformation is adopted here to deduce the solutions of crack tip stress concentration. The fracture propagation criterions have been put forward when the perpendicular to the minimum in-situ stress hydraulic fracture meets oblique bedding by considering shale reservoirs heterogeneity as well as strength anisotropy and then comparing fluid pressure satisfied fracture propagation in all directions. In order to show how difficult the hydraulic fracture turning to bedding, the critical strength ratios of bedding and rock mass are defined respectively when the fracture just initiates in bedding and propagates along bedding. Based on these two critical strength ratios, the bedding strength range which fracture initiates in bedding and propagates along bedding can be obtained. Analytical analysis show as follows:the critical strength ratio of bedding crack initiation increases with the decrease of bedding strike angle and dip angle and the increase of min-principal stress and the rock strength. The critical strength ratio of bedding crack initiation increases when the max-principal stress decreases and the middle-principal stress increase if the strike angle is less than 35.26°. Otherwise the critical strength ratio of bedding crack initiation decreases when the max-principal stress decreases and the middle-principal stress increase if the strike angle is greater than 35.26°. The critical strength ratio of bedding crack propagation increases when bedding strike angle, dip angle and in-situ stress difference decrease and the rock strength increase. Only when the critical conditions of bedding crack initiation and propagation all are satisfied do the hydraulic fractures turn to bedding.

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