Experimental performance of selective simultaneous water alternating nitrogen (SSWAG-N2) technique for oil recovery in sandstone and carbonate

Although there were techniques such as Water Alternating Gas-Nitrogen (WAG-N2) to minimize the problems of viscous fingering and density tonging; however, water gas segregation problem occurred. Water gas segregation leads to early Water Breakthrough and Gas Breakthrough. In this study, a technique of selective simultaneous water alternating gas (SSWAG-N2) was modified by injecting nitrogen gas at the lower part while water was injected at the higher part of the oil-producing zone. This technique was implemented to prolong the distance in the reservoir before water and gas segregation occurs; to delay water and gas breakthroughs. The main objective of this study was to investigate the effect of the modified SSWAG-N2 on the recoverability of sandstone and carbonate sand packs and the influence of Water and Gas Breakthroughs on the Oil Recovery Factor (ORF). This study also investigated the recoverability in conventional Enhanced Oil Recovery methods such as WF, GF, WAG, SSWAG process, and the early Water and Gas Breakthrough that usually associate these processes in order to compare them with the modified SSWAG-N2. A detailed comparison between the results of sandstone and carbonate sand packs has been achieved to investigate the effect of early water and gas breakthroughs on oil recovery of each method. In sandstone sand packs, three injection pressures: 2000 psi (137.9 bar), 1500 psi (103 bar), and 1000 psi (68.95 bar) were examined by studying the influence of injection pressure on delaying the water and gas breakthroughs; and consequently, prolong the distance before gas-water segregation. The better ORF inferred from this study when injecting N2 with brine using EOR injecting modes in sandstone and carbonate sand packs, was obtained when applying modified SSWAG-N2. In sandstone, the recoveries of the modified SSWAGN2 and conventional SSWAGN2, were 73.44, 71.95 respectively. Similarly, in carbonate, the recovery factor had the same arrangement with the following results: Modified SSWAG (73.72%), and conventional SSWAG (70.00%). The results of Oil Recovery Factor (ORF, %) in sandstone and carbonate sand pack cores were close. This added more reliability to the obtained results. Gas breakthrough (GBT) occurred at 39 min after implementation of the modified SSWAG; however, it occurred after 28 min in the conventional SSWAG in sandstone sand packs. Similarly, in carbonate sand packs, GBT occurred after 35 min in modified SSWAG compared with conventional SSWAG (21 min). During the implementation of the three different injection pressures, which were applied on sandstone sand packs using modified SSWAG technique, the better result of recovery was obtained when applying the injection pressure of 2000 psi and then followed by 1000 psi; whereas, the lowest recovery factor was when applying the injection pressure of 1500 psi