灰岩酸蚀裂缝软化区域力学特性与微观特征  

Mechanical properties and microscopic characteristics of acid etching softening layer in limestone fractures

作　　者：齐宁[1] 马世鑫 章泽辉 周顺明 邹浩然 李满亮[2] QI Ning;MA Shixin;ZHANG Zehui;ZHOU Shunming;ZOU Haoran;LI Manliang(School of Petroleum Engineering,China University of Petroleum(East China),Qingdao City,Shandong Province,266580,China;Northwest China Petroleum Bureau,SINOPEC,Urumqi,Xinjiang,830011,China)

机构地区：[1]中国石油大学(华东)石油工程学院,山东青岛266580 [2]中国石化西北油田分公司,新疆乌鲁木齐830011

出　　处：《油气地质与采收率》2024年第3期147-155,共9页Petroleum Geology and Recovery Efficiency

基　　金：国家科技重大专项“碳酸盐岩复合深度改造优化设计方法及配套技术研究”(2017ZX005030005);山东省自然科学基金项目“基于蚓孔竞争机制的自转向酸酸蚀蚓孔描述及动态酸化模拟研究”(ZR2017ME003)。

摘　　要：碳酸盐岩储层常采用酸化酸压工艺进行改造,酸蚀后岩石表面的微观结构被溶蚀破坏,岩石力学特性发生显著变化,进而影响最终的改造效果。为明确酸蚀对灰岩力学特性和微观孔隙结构变化的影响规律,开展了酸蚀前后灰岩力学特性实验、表面形态特征扫描电镜研究和微观孔隙结构核磁共振表征。结果表明,酸蚀后岩石表面出现了一定厚度的酸蚀软化层,厚度约为11.61μm。值得注意的是,由于酸蚀软化层的存在,灰岩抗压强度、弹性模量与表面硬度均降至酸蚀前的约40%。酸蚀后表层岩石内部产生了大小不一的溶蚀孔洞,并在溶蚀孔洞周边引发应力集中,改变了酸蚀软化层的应力分布。在高闭合应力作用下,溶蚀孔洞易于发生挤压变形或坍塌破坏,这也是酸蚀软化层力学性质改变的主要原因。结合核磁共振T2谱,发现孔径尺寸在1nm~1μm的孔隙数量变化最大,酸液溶蚀改变了灰岩软化层内部的孔隙结构,进而显著影响酸蚀后岩石的力学性质。Carbonate reservoirs are often stimulated by acidizing and acid fracturing techniques,but the microstructure of the rock surface is corroded and destroyed after acid etching,and the mechanical properties of the rock are changed significantly,which further affects the final stimulation effect.The experiment on the mechanical properties,the study on surface morphological characteristics by scanning electron microscopic(SEM),and the microscopic pore structure characterization by nuclear magnetic resonance(NMR)are carried out before and after limestone acid etching to clarify the influence of acid etching on the mechanical properties and microscopic pore structure changes of limestone.The results show that acid etching softening layers with a certain thickness of about 11.61μm appear on the rock surface after acid etching.Remarkably,the compressive strength,elastic modulus,and surface hardness of limestone are all reduced to about 40%before acid etching due to the acid etching softening layers.Dissolved pores of different sizes are formed inside the rock surface after acid etching and stress concentration is induced around the dissolved pores,changing the stress distribution of the acid etching softening layers.Under high closure stress,the dissolved pores are easier to crush deformation or collapse failure,which is also the main reason for the change of mechanical properties of acid etching softening layers.According to the T2 spectrogram of NMR,it is found that there is the largest change in the number of pores with pore sizes between 1 nm and 1μm,and the acid dissolution alters the internal pore structures of the acid etching softening layers,hence further affecting the mechanical properties of rock after acid etching.

关 键 词：灰岩 酸蚀软化 孔隙特征 力学特性 酸压 

分 类 号：TE341[石油与天然气工程—油气田开发工程]