The physical simulation experiment of lean gas injection in high-pressure and low-permeability reservoirs

During lean gas reinjection after depletion in high-pressure and low-permeability reservoirs, the fluid composition in the formation changes greatly, the microscopic interaction process among fluids is complex, and the microscopic mechanism of lean gas flooding is not clear to us. In this article, the microscopic experiments were carried out in high-temperature and high-pressure micro-visualization experiment apparatus of independent research and development. The microscopic interaction process between lean gas and formation fluid before and after depletion was studied on the porous models made of glass by etching. The flow law of lean gas after depletion and the mechanism of microscopic oil displacement were discussed. The results from experiments conclude that lean gas flooding should alleviate the Jamin effect caused by gas separated from oil during depleted production. Under the reservoir conditions, the oil is produced by lean gas displacement force primarily, by lean gas extraction for auxiliary. The water barrier prevents the contact between lean gas and residual oil. In unswept areas of lean gas, the residual oil is difficult to be produced as the poor diffusion of lean gas through water barrier into residual oil. While in swept area, lean gas can peel off water film gradually, then contact with residual oil directly, and then drive out oil by dissolving and extracting. Lean gas flooding in high-pressure and low-permeability reservoirs can enhance oil recovery further after depleted production.