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我国很多油气田在投入开发初期就进行了压裂,获得了很好的开发效果。但目前主力油气田大多都已进入开发中后期,重复压裂作为老油气田稳产的技术措施,是亟待研究的重大课题。而现行的重复压裂技术大致延原裂缝方向延长且存在水力压裂的普遍问题所以不能完全满足我们的需求。于是我们提出将液氮压裂技术应用于重复压裂。该技术将低温高压的液氮压入地层。充入原裂缝的液化氮气在地层内吸热迅速汽化,体积急速膨胀,同时岩石温度由地层高温迅速降低到液氮汽化的温度(约77K),使岩石的体积收缩产生各向裂缝形成网络。作为重复压裂弥补了液氮压裂液冲击力不足难以形成大口径裂缝的缺陷,也解决了普通重复压裂裂缝方向单一的缺点。
Many oil and gas fields in our country were fractured in the early stage of investment and development, and achieved good development results. However, at present, most of the major oil and gas fields have entered the middle and late stages of development. Repeated fracturing, as a technical measure to stabilize production in old oil and gas fields, is a major issue that needs urgent study. However, the current technology of repeated fracturing extends the fracture direction and extends the general problem of hydraulic fracturing. Therefore, it can not fully meet our needs. So we propose to apply liquid nitrogen fracturing technology to repeated fracturing. The technology will be low temperature and pressure liquid nitrogen into the formation. The liquefied nitrogen filled into the original fractures vaporizes rapidly in the formation and rapidly expands in volume. At the same time, the temperature of the rock rapidly decreases from the high temperature of the formation to the temperature of liquid nitrogen vaporization (about 77K), causing the volumetric shrinkage of the rock to form an all-directional fracture network. As the repeated fracturing to make up for the impact of liquid nitrogen fracturing fluid is difficult to form large-diameter fracture defects, but also to solve the common direction of a single crack fracturing the shortcomings.