AN EXPERIMENTAL INVESTIGATION OF GRAVITY DRAINAGE DURING IMMISCIBLE GAS INJECTION IN CARBONATE ROCKS UNDER RESERVOIR CONDITIONS

Gravity drainage is one of the important recovery mechanisms in fractured carbonate and conventional reservoirs. It occurs due to density difference between the gas in fracture and the oil in matrix as well as in conventional tilted reservoirs. Oil phase will form films which are produced under gravity forces (film flow). Many gas injection experiments have been done on laboratory scales with dead oil, but, herein, we would like to recombine oil under reservoir conditions. In this paper, the gravity drainage process is considered during immiscible gas injection in carbonate core saturated with recombined oil at reservoir temperature and pressure. Recombined oil was prepared from dead oil and a solvent (methane and propane) mixed in recombination apparatus. In these experiments, nitrogen gas is injected in a single matrix block at different rates and directions. Since the recovery of oil depends on the gas injection flow rate, the recovery of oil is maximized at a specific flow rate. The results show that gas injection at gravity drainage rate gives the maximum recovery, and ultimate recovery decreases at much higher injection rates. Comparing the gas injection results in horizontal and vertical directions shows that the recovery is higher in the vertical direction than the horizontal direction.