No abstract

After the near-abandoned production wells in the high part of the fault block reservoir are closed for a period of time, the remaining oil in the low part will accumulate at the fault in the high part to produce secondary enrichment. At present, research on the secondary enrichment of the remaining oil mainly focuses on the remigration method of the remaining oil, and there is less research on the mechanism of the secondary enrichment of the remaining oil. In view of the above problems, a planar numerical model is established to analyse the remaining oil secondary enrichment law, combined with the longitudinal numerical model to analyse the mechanism of the remaining oil secondary enrichment, and nine factors are selected to study their influence on the remaining oil secondary enrichment law, further determining the main control factors through sensitivity analysis. Based on the numerical simulation results, the reservoir conditions conducive to the secondary enrichment of the remaining oil are determined. The research shows that the remaining oil secondary enrichment mechanism includes pressure redistribution after well shut-in and the comprehensive effect of the micro force. The increase in the formation dip angle, permeability and water injection intensity before well shut-in is beneficial to accelerate the secondary enrichment of the remaining oil. Permeability and formation dip angle are the main controlling factors of positive correlation parameters, and the shut-in water cut is the main controlling factor of negative correlation parameters and the most sensitive. In addition, when the permeability is greater than 200 mD, the formation dip angle is greater than 9°, and the shut-in water cut is less than 95%, which is conducive to the secondary enrichment of the remaining oil. This study has reference significance for the field to understand the mechanism and influencing factors of the secondary enrichment of the remaining oil.

CO 2 miscible flooding in low permeability reservoirs is conducive to significantly improving oil recovery. At present, the microscopic displacement simulation of CO 2 miscible flooding is mainly reflected in the simulation of the seepage process, but the pressure control of the seepage process is lacking, and the simulation of the characterization of CO 2 concentration diffusion is less studied. In view of the above problems, a numerical model of CO 2 miscible flooding is established, and the microscopic seepage characteristics of interphase mass transfer in CO 2 miscible flooding are analyzed by multiphysics field coupling simulations at the two-dimensional pore scale. The injection velocity, contact angle, diffusion coefficient, and initial injection concentration are selected to analyze their effects on the microscopic seepage characteristics of CO 2 miscible flooding and the concentration distribution in the process of CO 2 diffusion. The research shows that after injection into the model, CO 2 preferentially diffuses into the large pore space and forms a miscible area with crude oil through interphase mass transfer, and the miscible area expands continuously and is pushed to the outlet by the high CO 2 concentration area. The increase in injection velocity will accelerate the seepage process of CO 2 miscible displacement, which will increase the sweep area at the same time. The increase in contact angle increases the seepage resistance of CO 2 and weakens the interphase mass transfer with crude oil, resulting in a gradual decrease in the final recovery efficiency. When the diffusion coefficient increases, the CO 2 concentration in the small pores and the parts that are difficult to reach at the model edge will gradually increase. The larger the initial injection concentration is, the larger the CO 2 concentration in the large pore and miscible areas in the sweep region at the same time. This study has guiding significance for the field to further understand the microscopic seepage characteristics of CO 2 miscible flooding under the effect of interphase mass transfer.