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页岩气储层水力裂缝转向扩展机制
陈勉
0
(中国石油大学石油工程学院,北京 102249)
摘要:
从页岩储层岩石断裂力学角度出发,推导三维空间中水力裂缝激活和转向控制方程,将转向扩展的水力裂缝视为不连续正应力条件下的连续延伸。分析控制裂缝转向扩展形态的关键因素和力学特征并进行实例计算。结果表明:从主裂缝扩展长度方向看,水平地应力差越大,裂缝转向后宽度越窄;压裂液排量和黏度越大,裂缝转向后剩余能量越大,裂缝宽度越大;水力裂缝和天然裂缝初始逼近角约为30°时最容易沿天然裂缝发生转向;水力裂缝发生转向后表观形态有较大变化,裂缝向偏离最大主应力方向扩展,造成裂缝宽度变窄;裂缝打开能量的过多耗散造成裂缝总体长度和体积变小;水力裂缝转向能扩展为2~3种裂缝模式的复合。
关键词:  页岩气  水力裂缝  转向扩展  裂缝形态  岩石力学
DOI:10.3969/j.issn.1673-5005.2013.05.013
投稿时间:2013-07-11
基金项目:国家自然科学基金项目(51234006)
Re-orientation and propagation of hydraulic fractures in shale gas reservoir
CHEN Mian
(College of Petroleum Engineering in China University of Petroleum, Beijing 102249, China)
Abstract:
A three-dimensional model for reactivation and re-orientation of hydraulic fractures in shale gas reservoir was established based on the theory of rock fracture mechanics. The re-orientation of fractures was considered as a continuous propagation process under discontinuous normal stress. Important factors and mechanical characteristics that affect fracture 's geometry were studied in real cases. The results show that, in the direction of main fracture propagation, fracture width dramatically narrows after re-orientation when high horizontal differential stress is subjected. Higher pump rate and higher viscosity of the fracture fluid can generate a wider fracture because higher residual energy is provided after the re-orientation. When the initial angle between hydraulic and natural fractures nears to 30°, the hydraulic fracture tends to re-orientation more easily along the natural fractures. The propagation of the hydraulic fracture after its re-orientation will deviate from the maximum horizontal stress direction, resulting in shorter fracture length and smaller volume since more energy was lost in the re-orientation process. After the re-orientation, the hydraulic fracture can become a complicated fracture network with two to three modes.
Key words:  shale gas  hydraulic fracture  fracture re-orientation and propagation  fracture geometry  rock mechanics
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