Enhance liquid nitrogen fracturing performance on hot dry rock by cyclic injection  

作　　者：Chun-Yang Hong Rui-Yue Yang Zhong-Wei Huang Xiao-Ying Zhuang Hai-Tao Wen Xiao-Li Hu 

机构地区：[1]State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing,102249,China [2]Chair of Computational Science and Simulation Technology,Faculty of Mathematics and Physics,Leibniz Universität Hannover,Hannover,30167,Germany

出　　处：《Petroleum Science》2023年第2期951-972,共22页石油科学（英文版）

基　　金：supported by the Youth Program of the National Natural Science Foundation of China(52004299);Major Project of the National Natural Science Foundation of China(52192621);the National Science Foundation for National R&D Program for Major Research Instruments of China(51827804);Beijing Outstanding Young Scientist Program(BJJWZYJH01201911414038);the National Science Foundation for Distinguished Young Scholars of China(51725404).

摘　　要：Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown pressure and results only in single main fracture morphology. Furthermore, HF has also other problems such as the increased risk of seismic events and consuption of large amount of water. In this work, a new stimulation method based on cyclic soft stimulation (CSS) and liquid nitrogen (LN2) fracturing, known as cyclic LN2 fracturing is explored, which we believe has the potential to solve the above issues related to HF. The fracturing performances including breakdown pressure and fracture morphology on granites under true-triaxial stresses are investigated and compared with cyclic water fracturing. Cryo-scanning electron microscopy (Cryo-SEM) tests and X-ray computed tomography (CT) scanning tests were used for quantitative characterization of fracture parameters and to evaluate the cyclic LN2 fracturing performances. The results demonstrate that the cyclic LN2 fracturing results in reduced breakdown pressure, with between 21% and 67% lower pressure compared with using cyclic water fracturing. Cyclic LN2 fracturing tends to produce more complex and branched fractures, whereas cyclic water fracturing usually produces a single main fracture under a low number of cycles and pressure levels. Thermally-induced fractures mostly occur around the interfaces of different particles. This study shows the potential benefits of cyclic LN2 fracturing on HDR. It is expected to provide theoretical guidance for the cyclic LN2 fracturing application in HDR reservoirs.

关 键 词：Hot dry rock Liquid nitrogen fracturing Cyclic injection Thermal stress Fatigue damage 

分 类 号：TE357.6[石油与天然气工程—油气田开发工程]