Experimental investigation of heavy oil recovery from fractured reservoirs by secondary steam - Gas assisted gravity drainage

In this study, gas-oil gravity drainage process and steam-gas assisted gravity drainage processes for heavy oil recovery from fractured models were investigated experimentally. For each test, six oil- wet saturated outcrop cores, 8.7 cm in diameter and 15 cm length, were stacked in a long core holder. In the first step, gas injection was started into the model at reservoir condition that results in oil production under gas-oil gravity drainage mechanism. In the second round of tests when no more oil was produced by gas injection, the tests were continued using steam-gas assisted gravity drainage process. In this stage, gas was injected together with specific steam/gas ratio at saturated temperature condition. In the course of experiments, oil and water productions, pressure and temperatures of system were monitored carefully. The experiments were performed using three different combination of gases consist of pure CO₂, pure N₂ and mixture of 15 % CO₂ and 85% N₂ as synthetic flue gas. The results showed that after gas breakthrough and fracture depletion, the ultimate oil recovery for CO ₂ injection was 58.4 % (14.8% for gas injection and 43.6 % for steam-gas co-injection), in the case of flue gas injection, it was 73.8 % (9.8 % for gas injection and 64% for steam-gas co-injection) and for N₂ injection was 47% (13.5 % for gas injection and 33.5% for steam-gas co-injection). The results indicate the high performance of flue gas injection for heavy oil recovery from fractured reservoirs during gas-oil gravity drainage and steam-gas assisted gravity drainage processes.