Comparative analysis of the fracturing effect of H2O, liquid CO2, and supercritical CO2 on tight sandstone reservoir

Abstract

At present, tight oil and gas reservoirs exploitation mainly adopts water (H2O)-based fracturing technology, which not only consumes huge amounts of water, but also restricts the process of industrial exploitation in water-scarce areas. In addition, the clay will expand in contact with water, resulting in poor reservoir stimulation effect and low recovery factor. In order to avoid the problems caused by hydraulic fracturing, carbon dioxide fracturing is used to replace hydraulic fracturing technology, so as to achieve the purpose of reservoir stimulation. While transforming the reservoir, CO2 fracturing technology can also realize the geological storage of CO2, thus achieving the ultimate goal of carbon capture, utilization and storage (CCUS). In this study, comparative experiments of H2O-based, L-CO2 and SC-CO2 fracturing with core holder, porosity, permeability and CT scanning tests were carried out to study the breakdown pressure of the sandstone samples used in the experiment and the internal reconstruction images obtained. The research results show that with the increase of fracturing pressure, the viscosity of H2O remained unchanged, and the viscosity of L-CO2 and SC-CO2 increased slowly. Compared with hydraulic fracturing and L-CO2 fracturing, the porosity and permeability of shale fracturing with SC-CO2 are the highest. In particular, the permeability of post-fractured cores after SC-CO2 fracturing was three orders of magnitude higher than that of H2O-based and L-CO2 fracturing, the permeability of SC-CO2 fracturing was 8.4139md, while the permeability of L-CO2 and H2O fracturing was only 0.01 md and 0.009md, respectively. In addition, hydraulic fracturing is more likely to produce smooth single fractures in the highest pressure regions of the shale sample. L-CO2 fracturing is prone to produce short and small main fractures, accompanied by the formation of micro-fractures. Sc-CO2 fracturing has the potential to form a local fracture network, and the required penetration pressure is the lowest.

Keywords: tight sandstone reservoir, H2O-based fracturing, CO2-fracturing, supercritical CO2, fracture propagation, CO2 geological storage