Compared with hydraulic fracturing, CO2 waterless fracturing can an alternative technology for the unconventional resources, such as the tight oil resources and the tight gas resources. It is an environment-friendly fracturing technology. Liquid CO2 fluid can be more easily obtained, and it is safe and non-explosive. Under formation temperature, it has ultra-low interfacial tension in supercritical state, so it has strong penetration ability, which can penetrate into matrix of reservoir and communicate with reservoir deeply. At the same time, it can reduce the viscosity of crude oil. Therefore, it is a kind of ideal fracturing fluid. This technology is significant for clean and efficient development of low-permeability tight oil reservoirs, and worthy of broad application.
The technique is divided into three stages. The large-scale high-pressure injection of liquid CO2 after fracturing, fracturing, continue to inject CO2 throughput, through multiple rounds, cyclic injection, CO2 from the wellbore along the cracks gradually extended to the distal end, increase formation energy, the single well control range and improve the producing rate of the reserves, at the same time to dissolve crude oil extraction, oil viscosity decrease. The CO2 steam soak, enhanced oil recovery rate decreased gradually, while the enhanced oil recovery rate is lower than the economic limit, the implementation of CO2 refractured, further increase the transformation volume, continue to inject CO2 multi cycle throughput, the CO2 can be extended to the depths of the reservoir, and further improve the reserves rate and yield of single well. When the pressure of production wells spread to neighboring distal production wells, injection wells will be part of the production of CO2, forming a rectangle of five wells net, CO2 flooding, establish effective displacement pressure system, supplement the formation energy, to ensure long-term stable production of tight oil wells.
The integrated technology of CO2 waterless fracturing has been used in ten tight oil wells of the north Oilfield in China. During the fracturing. In this treatment 19.8 m3 of proppant and 653.5m3 of liquid CO2 is used. As a result, the production has increased by over 100%. With low viscosity and high diffusion coefficient, supercritical CO2 is good for improving fracturing volume.
In the tight oil reservoir, The realization of artificial energy development, reducing carbon emissions, to further enhance oil recovery, improve the reservoir producing ability. At the same time, to realize large-scale CO2 sequestration and reduce carbon emissions, both realistic and economic, but also great social benefits.