Key problems and solutions in supercritical CO₂ fracturing technology

Abstract

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.

Key words： supercritical CO₂; fracturing; friction loss; proppant carrying; flied test problem

Acknowledgments

This study was supported by the National Natural Science Foundation of China (Grant Nos.51221003, 51874318), the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2017ZX05039-003).

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