1. 中国石油大学（北京）油气资源与探测国家重点实验室 2. 中国石油国际勘探开发有限公司 3. Department of Petroleum and Geosystems Engineering, University of Texas at Austin, Austin, TX, USA, 78712
Key problems and solutions in supercritical CO2 fracturing technology
1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China 2. China National Oil and Gas Exploration and Development Co., Ltd, Beijing 100034, China 3. Hildebrand Department of Petroleum and Geosystems Engineering, University of Texas, Austin TX 78712, USA
Supercritical CO2 fracturing is considered to be a new method for efficient exploitation of unconventional reservoirs, such as shale gas, coal bed methane, and tight sand stone gas. Supercritical CO2 has many special properties including low viscosity, high diffusion coefficient, and lack of surface tension, which brings about great advantages for fracturing. However, these properties also cause several problems, such as difficulty in proppant transportation, high friction loss, and high pump displacement. In this paper, the above problems were analyzed by combining field test with laboratory study and specific solutions to these problems are given. The high frictionloss in the pipeline could be reduced by developing a new drag reducing agent and selecting large-size casing. Besides, for the problem of poor capacity in proppant carrying and sand plug, the methods of adding tackifier into supercritical CO2, increasing pump displacement and selecting ultra-low density proppants are proposed. Moreover, for the problem of fast leak-off and high requirement for pump displacement, the displacement can be increased or the pad fluid can be injected into the reservoir. After solving the above three problems, the field test of supercritical CO2 fracturing can be conducted. The research results can promote the industrialization process of supercritical CO2 fracturing.
Jet fracturing tool with with 8-hole 6.5 mm diameter nozzle
2.7
7.5
27
Tab.2
60°C
70°C
80°C
90°C
40 MPa
60 MPa
40 MPa
60 MPa
40 MPa
60 MPa
40 MPa
60 MPa
Viscosity
SC-CO2/(mPa·s)
0.0893
0.1000
0.0823
0.1023
0.0762
0.0957
0.0708
0.0899
Water/(mPa·s)
0.4760
0.4813
0.4143
0.4197
0.3650
0.3705
0.3252
0.3306
Tab.3
Fig.3
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