摘要
液氮压裂是一种采用温度极低的液氮对储层进行压裂的方法。与常规压裂方式不同,液氮的超低温作用会使得储层岩石温度急剧降低,产生强烈的温度应力,诱导储层岩石产生裂缝。为探究液氮超低温作用诱导岩石裂缝的起裂和扩展机制,分别对裸眼井筒、预制裂缝和水力裂缝进行液氮超低温冲击作用模拟实验,获得诱导裂缝分布特征,并测量超低温冲击作用过程中井筒径向和预置裂缝法向温度场变化,研究最大拉应力准则和应力强度因子断裂准则,判定超低温诱导裂缝扩展范围的适用性。结果表明,超低温诱导裂缝主要垂直于裸眼井筒井壁、预制裂缝和水力裂缝等已有裂缝面起裂,且诱导裂缝两侧同样会出现垂直于诱导裂缝起裂的次级诱导裂缝,形成复杂裂缝网络。根据超低温诱导裂缝扩展尺度的实验结果,提出采用最大拉应力准则和应力强度因子断裂准则分别判定诱导裂缝扩展长度下限和上限的方法。此外,提出水力压裂结合液氮压裂改造储层的方法,并进行实验验证。研究结果为液氮压裂可行性和设计提供了依据。
Liquid nitrogen(LN;)fracturing is a method of stimulating reservoir with ultra-low temperature LN;.Different from the conventional fracturing methods,the ultra-low temperature impact of LN;will sharply reduce the reservoir rock temperature,produce strong temperature stress and induce fractures in the reservoir rock.To explore the initiation and propagation mechanisms of rock fractures induced by LN;ultra-low temperature,LN;ultra-low temperature impact simulation experiments were carried out on open-hole wellbores,preset fractures and hydraulic fractures respectively.The distribution characteristics of induced fractures were obtained,and the changes of the temperature fields along the radial direction of the open-hole wellbores and the normal direction of the preset fractures during ultra-low temperature impact were measured.The applicability of the maximum tensile stress criterion and the stress intensity factor fracture criterion to determine the fracture propagation range induced by ultra-low temperature was studied.The results show that the initiation of the ultra-low temperature induced fractures are mainly perpendicular to the existing fracture surface such as the open-hole wellbore wall,the preset fracture and the hydraulic fracture,and the secondary induced fractures perpendicular to the induced fractures also appear on both sides of the induced fractures,forming a complex fracture network.According to the experimental results of fracture propagation scale,the maximum tensile stress criterion and the stress intensity factor fracture criterion are proposed to determine the lower and upper limits of the induced fracture propagation length respectively.In addition,the method of hydraulic fracturing combined with LN;fracturing was proposed and verified by experiments.The research results provide a basis for the feasibility and design of LN;fracturing.
作者
郑学林
张广清
郑士杰
ZHENG Xuelin;ZHANG Guangqing;ZHENG Shijie(College of Petroleum Engineering,China University of Petroleum(Beijing),Beijing 102249,China)
出处
《岩石力学与工程学报》
EI
CAS
CSCD
北大核心
2022年第5期889-903,共15页
Chinese Journal of Rock Mechanics and Engineering
基金
国家自然科学基金资助项目(51774299)
国家杰出青年科学基金资助项目(51925405)。
关键词
岩石力学
液氮压裂
温度作用
诱导裂缝
多级分支裂缝
rock mechanics
liquid nitrogen fracturing
temperature impact
induced fractures
multistage branch fractures
