Fracture propagation mechanism and application of supercritical CO2 fracturing in shale: A review

Abstract

With the increasing demand for energy, traditional oil resources are facing depletion and insufficient supply. Many countries are rapidly turning to the development of unconventional oil and gas resources. Among them, shale oil and gas reservoirs have become the focus of unconventional oil and gas resources exploration and development. Based on the characteristics of shale oil and gas reservoirs, supercritical CO 2 fracturing is more conducive to improving oil recovery than other fracturing technologies. In this paper, the mechanism of fracture initiation and propagation of supercritical CO 2 in shale is analyzed, including viscosity effect, surface tension effect , permeation diffusion effect of supercritical CO 2 , and dissolution-adsorption effect between CO 2 and shale. The effects of natural factors, such as shale properties, bedding plane and natural fractures , and controllable factors, proppant , temperature, pressure, CO 2 concentration and injection rate on fracture initiation and propagation are clarified. The methods of supercritical CO 2 fracturing process, thickener and proppant optimization to improve the efficiency of supercritical CO 2 fracturing are discussed. In addition, some new technologies of supercritical CO 2 fracturing are introduced. The challenges and prospects in the current research are also summarized. For example, supercritical CO 2 is prone to filtration when passing through porous media, and it is difficult to form a stable flow state. Therefore, in order to achieve stable fracturing fluid suspension and effectively support fractures, it is urgent to explore new fracturing fluid additives or improve fracturing fluid formulations combined with the research of new proppants. This paper is of great significance for understanding the behavior mechanism of supercritical CO 2 in shale and optimizing fracturing technology.

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