石灰岩酸压裂缝蠕变闭合机理研究  

Creep closure mechanism of acid-etched fractures in limestone

作　　者：齐宁[1,2] 马腾飞 章泽辉 刘湘华 刘练 QI Ning;MA Tengfei;ZHANG Zehui;LIU Xianghua;LIU Lian(College of Petroleum Engineering,China University of Petroleum-East China,Qingdao,Shandong 266580,China;Key Laboratory of Unconventional Oil&Gas Development,Ministry of Education//China University of Petroleum-East China,Qingdao,Shandong 266580,China;Sinopec Northwest Oilfield Company,Urumqi,Xinjiang 830011,China)

机构地区：[1]中国石油大学(华东)石油工程学院,山东省青岛市266580 [2]非常规油气开发教育部重点实验室·中国石油大学(华东),山东省青岛市266580 [3]中国石化西北油田分公司

出　　处：《天然气工业》2024年第12期73-82,共10页Natural Gas Industry

基　　金：山东省自然科学基金面上项目“深层碳酸盐岩酸压酸蚀裂缝导流能力演化规律研究”(编号:ZR2024ME106)。

摘　　要：石灰岩储层渗透率低、非均质性强,油气开发过程中常采用酸压进行储层改造,但酸蚀后岩石力学性质会发生明显改变,在高闭合压力作用下酸蚀裂缝的稳态蠕变速率显著增大,裂缝更容易发生蠕变闭合,致使导流能力下降甚至丧失,揭示酸蚀石灰岩蠕变机理对于深层油气储层改造与高效开发具有重要意义。为此,在研究酸蚀石灰岩蠕变特征基础上,提出了酸蚀石灰岩的蠕变方案及模型,结合酸蚀石灰岩的三轴蠕变实验,采用ABAQUS有限元分析方法,研究了石灰岩酸蚀后蠕变和酸蚀裂缝壁面微凸体对导流能力的影响。研究结果表明:①石灰岩酸蚀后表现出显著的蠕变特性,低围压时,酸蚀石灰岩峰值强度显著下降,高围压时,酸化对石灰岩峰值强度影响不大;②在初始蠕变阶段与稳态蠕变阶段、稳态蠕变阶段与加速蠕变阶段之间没有明显的界限;③轴向应力是控制酸蚀裂缝闭合的主控因素,酸蚀软化层的存在使石灰岩裂缝的强度显著下降,软化层承担的应力是酸蚀石灰岩内部的4~6倍;④酸蚀石灰岩裂缝的蠕变本构关系满足虎克体与麦克斯韦尔体的并联关系,酸蚀石灰岩裂缝的蠕变表现出滞弹性。结论认为,虎克体与麦克斯韦尔体的并联模型可有效预测酸蚀石灰岩的蠕变特性,提高了深层石灰岩油气藏酸化酸压作业风险防范效率,为深层、超深层石灰岩储层改造与高效开发提供理论指导,建议持续深化对酸蚀后不同岩性岩石力学特性的研究,以推动石灰岩储层改造的技术创新和高质量发展。Limestone reservoirs are of low permeability and high heterogeneity,and acid fracturing is often employed for reservoir stimulation in the development of such oil and gas reservoirs.After being acid etched,however,limestone changes significantly in mechanical properties.Under high closure pressure,the steady-state creep rate of acid-etched fractures increases greatly,making these fractures more susceptible to creep closure,which can lead to a decline or even a complete loss of conductivity.Therefore,revealing the creep mechanism of acid-etched limestone is crucial for the stimulation and efficient development of deep oil and gas reservoirs.In this paper,a creep pattern and a model of acid-etched limestone are proposed by investigating the creep characteristics of acid-etched limestone.Then,a triaxial creep experiment of acid-etched limestone is carried out,and the influences of creep of acid-etched limestone and the micro-asperity on the wall surface of acid-etched fractures on conductivity are studied by using the ABAQUS finite element analysis method.And the following research results are obtained.First,acid-etched limestone exhibits pronounced creep characteristics,with a significant reduction in peak strength at low confining pressures,but less influence of acidizing on peak strength at high confining pressures.Second,there is no distinct boundary between the initial creep stage and the steady-state creep stage,nor between the steadystate creep stage and the accelerated creep stage.Third,axial stress is the main factor controlling the closure of acid-etched fractures,the presence of the acid-etching softened layer significantly reduces the strength of the limestone fractures,and the stress applied on the softened layer is 4 to 6 times that within the acid-etched limestone.Fourth,the creep constitutive relationship of acid-etched limestone fractures conforms to a parallel model of Hookean and Maxwell bodies,exhibiting anelastic behaviors.In conclusion,the parallel model of Hookean and Maxwell bodies can effect

关 键 词：石灰岩酸蚀蠕变 裂缝闭合 酸蚀软化层 微凸体 蠕变本构模型 麦克斯韦尔模型 ABAQUS有限元分析 

分 类 号：TE357[石油与天然气工程—油气田开发工程]