不同相态二氧化碳前置酸压碳酸盐岩裂缝形成规律  

Formation of fractures in carbonate rocks by pad acid fracturing with different phases of carbon dioxide

作　　者：郭建春[1] 詹立 苟波[1] 张然 刘超 李骁 任冀川 GUO Jianchun;ZHAN Li;GOU Bo;ZHANG Ran;LIU Chao;LI Xiao;REN Jichuan(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China;College of Mechanical Engineering,Xihua University,Chengdu 610500,China;Research Institute of Yanchang Petroleum(Group)Co.Ltd,Xi'an 710065,China;Shaanxi Key Laboratory of Lacustrine Shale Gas Accumulation&Exploitation(under planning),Xi'an 710065,China)

机构地区：[1]西南石油大学油气藏地质及开发工程国家重点实验室,成都610500 [2]西华大学机械工程学院,成都610500 [3]陕西延长石油(集团)有限责任公司研究院,西安710065 [4]陕西省陆相页岩气成藏与开发重点实验室(筹),西安710065

出　　处：《石油勘探与开发》2021年第3期639-645,共7页Petroleum Exploration and Development

基　　金：国家自然科学基金项目“裂缝型碳酸盐岩温度-裂缝渗流-酸岩反应-应力损伤耦合酸化机理研究”(51704249);油气藏地质及开发工程国家重点实验室开放基金资助项目“不同相态CO_(2)作用下煤岩裂缝扩展机理研究”(PLN2020-1)。

摘　　要：选取延安气田下古生界马五1亚段碳酸盐岩露头,开展了清水、液态CO_(2)、超临界CO_(2)作用下的真三轴压裂实验,同时采用CT扫描技术,分析了碳酸盐岩中压裂裂缝的起裂和扩展规律。研究表明,超临界CO_(2)黏度低,扩散性强,压裂过程中滤失量大,有利于提高井筒周围岩石孔隙压力,明显降低碳酸盐岩的破裂压力,但压裂过程中井筒压力上升缓慢,致裂岩石所消耗的超临界CO_(2)体积远大于清水;天然裂缝不发育的碳酸盐岩,采用清水、液态CO_(2)压裂易发生张性破坏,压裂裂缝主要沿最大水平主应力方向扩展,采用超临界CO_(2)压裂易发生剪性破坏且水平应力差对压裂裂缝形态影响较小,近井筒处压裂裂缝扩展方向与最大水平主应力方向呈45°夹角,随扩展延伸距离的增加,在离井筒较远处逐渐转向最大水平主应力方向,裂缝迂曲度与前者相比有所增加;天然裂缝发育的碳酸盐岩,清水易沟通低逼近角天然裂缝,压裂后易形成“阶梯状”裂缝,裂缝形态相对简单,液态CO_(2)黏度低,易沟通高逼近角天然裂缝,压裂后易形成多方向缝,裂缝形态相对复杂,沟通高逼近角天然裂缝是碳酸盐岩压后形成复杂裂缝的关键。Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan'an gas field to conduct true tri-axial hydraulic fracturing experiments with water,liquid CO_(2) and supercritical CO_(2).CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks.The experiments show that supercritical CO_(2) has low viscosity,strong diffusivity and large filtration during fracturing,which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks.However,it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing.For carbonate rocks with few natural fractures,tensional fractures are generated by fracturing with water and liquid CO_(2),and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures,whose morphology is rarely influenced by horizontal stress difference.Besides,the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°,and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore,leading to an increase of fracture tortuosity compared with the former.For carbonate rocks with well-developed natural fractures,fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology.The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle.It is easier for liquid CO_(2) with low viscosity to realize such connection.Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).

关 键 词：碳酸盐岩 前置酸压 液态CO_(2) 超临界CO_(2) 裂缝起裂 裂缝扩展 

分 类 号：TE344[石油与天然气工程—油气田开发工程]