A mathematical model of CO2 miscible front migration in tight reservoirs with injection-production coupling technology

Abstract

The CO2 front migration law and the CO2 breakthrough are of great significance to both of the CO2 flooding and CO2 sequestration. Currently, the numerical simulation study on CO2 front migration mainly focused on the continuous CO2 miscible flooding, is time-consuming, and requires many experimental results, such as the crude oil composition obtained by PVT analyses and the minimum miscibility pressure (MMP) get by slim tube experiments. Besides, there is a little study on the CO2 miscible front migration of tight reservoirs with the injection-production coupling technology (IPCT) and few attentions are paid to build a correlation between the threshold pressure gradient (TPG) and CO2 concentration. In this paper, a correlation between the TPG and CO2 concentration is built firstly, and then a mathematical model of CO2 miscible front migration in tight reservoirs with IPCTs is proposed. The effects of parameters, such as the reservoir property, injection rate, CO2 adsorption, and injection-production cycle, on front migrations or CO2 breakthrough are analyzed, and the effects of continuous CO2 injection and IPCTs on the CO2 breakthrough is presented. From this work, it is concluded that the CO2 miscible flooding of IPCTs can alleviate the CO2 breakthrough when comparing with the continuous CO2 miscible flooding. The CO2 diffusion accelerates the CO2 breakthrough. The most important parameter that affects the CO2 breakthrough is the injection rate, followed by the adsorption effect, injection-production cycle time, and diffusion effect. When the injection volume in a cycle is a constant, a small injection-production cycle time can alleviate the CO2 breakthrough.