Browsing by Subject "SWAG"
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Item A simulation study to verify Stone's simultaneous water and gas injection performance in a 5-spot pattern(Texas A&M University, 2008-10-10) Barnawi, Mazen TaherWater alternating gas (WAG) injection is a proven technique to enhance oil recovery. It has been successfully implemented in the field since 1957 with recovery increase in the range of 5-10% of oil-initially-in-place (OIIP). In 2004, Herbert L. Stone presented a simultaneous water and gas injection technique. Gas is injected near the bottom of the reservoir and water is injected directly on top at high rates to prevent upward channeling of the gas. Stone's mathematical model indicated the new technique can increase vertical sweep efficiency by 3-4 folds over WAG. In this study, a commercial reservoir simulator was used to predict the performance of Stone's technique and compare it to WAG and other EOR injection strategies. Two sets of relative permeability data were considered. Multiple combinations of total injection rates (water plus gas) and water/gas ratios as well as injection schedules were investigated to find the optimum design parameters for an 80 acre 5-spot pattern unit. Results show that injecting water above gas may result in better oil recovery than WAG injection though not as indicated by Stone. Increase in oil recovery with SSWAG injection is a function of the gas critical saturation. The more gas is trapped in the formation, the higher oil recovery is obtained. This is probably due to the fact that areal sweep efficiency is a more dominant factor in a 5-spot pattern. Periodic shut-off of the water injector has little effect on oil recovery. Water/gas injection ratio optimization may result in a slight increase in oil recovery. SSWAG injection results in a steady injection pressure and less fluctuation in gas production rate compared to WAG injection.Item Experimental and Simulation Studies to Evaluate the Improvement of Oil Recovery by Different Modes of CO2 Injection in Carbonate Reservoirs(2011-02-22) Aleidan, Ahmed Abdulaziz S.Experimental and numerical simulation studies were conducted to investigate the improvement of light oil recovery in carbonate cores during CO2 injection. The main steps in the study are as follows. First, the minimum miscibility pressure of 31?API west Texas oil and CO2 was measured using the slimtube (miscibility) apparatus. Second, miscible CO2 coreflood experiments were carried out on different modes of injection such as CGI, WF, WAG, and SWAG. Each injection mode was conducted on unfractured and fractured cores. Fractured cores included two types of fracture systems creating two shape models on the core. Also, runs were made with different salinity levels for the injected water, 0 ppm, 60,000 ppm, and 200,000 ppm. Finally, based on the experimental results, a 2-D numerical simulation model was constructed and validated. The simulation model was then extended to conduct sensitivity studies on different parameters such as permeability variations in the core, WAG ratio and slug size, and SWAG ratio. The results of this study indicate that injecting water with CO2 either simultaneously or in alternating cycles increases the oil recovery by at least 10 percent and reduces the CO2 requirements by 50 percent. The salinity of the injected water has shown a detrimental effect on oil recovery only during WAG and SWAG injections. Lowering injected water salinity, which increases the CO2 solubility in water, increases oil recovery by up to 18 percent. Unfractured cores resulted in higher recovery than all fractured ones. CGI in fractured cores resulted in very poor recovery but WAG and SWAG injections improved the oil recovery by at least 25 percent over CGI. This is because of the better conformance provided by the injected water, which decreased CO2 cycling through the fracture. CO2 injection in layered permeability arrangements showed significant decrease in oil recovery (up to 40 percent) compared to the homogenous case. For all injection modes during the layered permeability arrangements, the best oil recovery was obtained when the flow barrier is in the middle of the core. When the permeability was arranged in sequence, each injection mode showed different preference to the permeability arrangements. The WAG ratio study in the homogenous case showed that a 1:2 ratio had the highest oil recovery, but the optimum ratio was 1:1 based on the amount of injected CO2. In contrast, layered permeability arrangements showed different WAG ratio preference depending on the location of the flow barrier.