不同煤体结构煤的水力压裂裂缝延伸规律

Fracture extension law of hydraulic fracture in coal with different structure

查明不同煤体结构煤水力压裂时裂缝延伸规律能为合理井网部署奠定基础。以沁水盆地柿庄区块为研究对象,对钻井煤心裂隙进行观测,划分出4种裂隙发育程度煤。基于岩体力学理论,建立了水力压裂过程中裂缝尖端应力场计算模型和水力裂缝能否穿过天然裂隙的判断准则。根据煤层气井实测资料,验证了理论分析的可靠性,得出了不同煤体结构煤的水力压裂裂缝延伸规律。结果表明:考虑诱导应力前后,2组天然裂隙发育煤的水力裂缝延伸规律不同,随着缝长增加,诱导应力随之增大,水力裂缝单一延伸方向变为双向延伸;1组天然裂隙发育煤的发育方向与最大主应力方向夹角较小,导致考虑诱导应力前后水力裂缝的延伸方向变化不明显,整体延伸趋于天然裂隙发育方向;在粒状偶见及粉状无裂隙发育煤中,水力裂缝总是沿着最大主应力方向延伸。研究成果为该区不同应力和裂隙发育下井网合理布置提供了理论依据。

To find out the fracture extension law of coal hydraulic fracturing with different coal body structures can lay a foundation for reasonable well pattern deployment.Taking Shizhuang block of Qinshui basin as the research object,the fracture of coal core was observed,and four kinds of coal with fracture development degree were divided.Based on the theory of rock mass mechanics,the stress field calculation model of fracture tip and the judgment criterion of whether hydraulic fracture can pass through natural fracture in hydraulic fracturing process were established.According to the measured data of CBM wells,the reliability of theoretical analysis was verified,and the fracture extension law of hydraulic fracturing of coal with different coal body structures was obtained.The results show that the hydraulic fracture extension of two groups of natural fracture development is different before and after the induced stress is considered.With the increase of fracture length,the induced stress increases,and the hydraulic fracture extends from single direction to bidirectional direction.For a group of coal with natural fracture development,because the angle between the development direction of natural fracture and the direction of maximum principal stress is small,the extension direction of hydraulic fracture before and after considering induced stress is not obvious,and the overall extension tends to the natural fissure development direction.Hydraulic fractures always extend along the direction of maximum principal stress for granular occasional and powdery fractured coal.The research results provide a theoretical basis for the reasonable arrangement of the well network under different stress and fracture development in this area.