天然裂缝对干热岩水力压裂裂缝扩展的影响规律  

Influence of natural fractures on the propagation of hydraulic fractures in hot dry rock

作　　者：谢紫霄 黄中伟[1] 熊建华[2] 武晓光[1] 李根生[1] 邹文超 龙腾达 XIE Zixiao;HUANG Zhongwei;XIONG Jianhua;WU Xiaoguang;LI Gensheng;ZOU Wenchao;LONG Tengda(State Key Laboratory of Petroleum Resources and Prospecting//China University of Petroleum,Beijing 102249,China;Sinopec Jiangsu Oilfield Company,Yangzhou,Jiangsu 225009,China)

机构地区：[1]油气资源与探测国家重点实验室·中国石油大学(北京) [2]中国石化江苏油田分公司

出　　处：《天然气工业》2022年第4期63-72,共10页Natural Gas Industry

基　　金：国家自然科学基金国际(地区)合作与交流项目“分支井眼辅助干热岩注采井缝网沟通机理研究”(编号:52020105001);国家自然科学基金重大项目“干热岩地热资源开采机理与方法”(编号:52192621);教育部高等学校学科创新引智基地(111计划)“深部地热资源开发基础研究”(编号:B17045);博士后创新人才支持计划“干热岩液氮压裂复杂缝网形成机理”(编号:BX20200382)。

摘　　要：地热能是一种清洁、环保的可再生能源,具有低碳环保、稳定高效等特点,水力压裂技术是有效开发干热岩地热资源的重要技术手段。目前高温花岗岩水力压裂时天然裂缝对水力裂缝扩展的影响未进行广泛地研究,对其水力裂缝扩展规律的认识尚不清楚。为此,以常见的干热岩类型(花岗岩)为研究对象,开展了实时高温下真三轴水力压裂实验,探究两种类型花岗岩在不同温度下的裂缝扩展特征及导流能力,揭示了干热岩水力裂缝在天然裂缝影响下的扩展规律,评价了压后裂缝的导流能力。研究结果表明:①随着花岗岩温度的上升,其起裂压力降低,裂缝面迂曲度提高,水力裂缝扩展路径更加随机;②不同温度下花岗岩压裂后裂缝的导流能力不同,随着花岗岩温度的上升,水力裂缝的导流能力也随之提高;③相同条件下,裂缝型花岗岩起裂压力低于致密型花岗岩的起裂压力,且压裂后裂缝型花岗岩的裂缝导流能力显著高于致密型花岗岩的裂缝导流能力。结论认为,寻找天然裂缝发育的干热岩储层是高效开发利用地热能的关键地质因素,实验结果对指导干热岩储层水力压裂提供了理论支撑,有助于我国地热资源的有效开发。Geothermal energy is a kind of clean and environmentally friendly renewable energy source and it is characterized by low carbon,environment protection,stability and high efficiency.Hydraulic fracturing is an important method to develop geothermal resources of hot dry rock(HDR)efficiently.At present,however,the influence of natural fractures on the propagation of hydraulic fractures during the hydraulic fracturing of high-temperature granite is not studied extensively and the propagation laws of hydraulic fractures are not clarified yet.Taking a common type of HDR(granite)as the research object,this paper carries out true-triaxial hydraulic fracturing experiments under high temperature in real time.Then,the propagation characteristics and conductivity of fractures in two types of granites under different temperatures are analyzed,the propagation laws of hydraulic fractures in HDR under the influence of natural fractures are revealed,and the fracture conductivity after fracturing is evaluated.And the following research results are obtained.First,with the increase of granite temperature,the fracturing initiation pressure decreases,but the tortuosity of fracture surface increases and the propagation paths of hydraulic fractures get more random.Second,the fracture conductivity after the fracturing of granite varies with temperatures.With the increase of granite temperature,the conductivity of hydraulic fractures also increases.Third,under the same situation,the fracturing initiation pressure of fractured granites is lower than that of tight granites and the fracture conductivity of fractured granites after fracturing is significantly higher than that of tight granites.In conclusion,searching for HDR reservoirs with developed natural fractures is the key geological factor to develop and utilize geothermal energy efficiently.The experimental results provide theoretical support for guiding hydraulic fracturing of HDR reservoirs and can promote the efficient development of domestic geothermal resources.

关 键 词：干热岩 真三轴水力压裂 水力裂缝 天然裂缝 裂缝扩展 起裂压力 裂缝导流能力 渗透系数 

分 类 号：P314[天文地球—固体地球物理学]