An experimental study of the effect of water saturation on cyclic N2 and CO2 injection in shale oil reservoir
Altawati, Faisal S.
The purpose of this study is to investigate the effect of the water saturation on oil recovery in shale oil reservoirs by cyclic N2 and CO2 Injection. The effect of water saturation on the oil recovery factor using Eagle Ford Shale outcrop cores was investigated. Cyclic gas injection technique was performed on Eagle Ford shale outcrop cores. Nitrogen and Carbon dioxide gases were used to conduct the experiments. First, some of core samples were saturated with heavy oil (Decane) only, and the other cores were partially saturated with water of 15 % of NaCl, then they were saturated with Decane. Afterwards, cyclic N2 and CO2 injection were conducted on all core samples at fixed soaking pressure (2000 psi), and under different conditions such as number of cycles, soaking periods, and production periods. The oil recovery data were analyzed. Initially, we attempted to find oil recovery from the cores partially saturated with water. Later, we found that we cannot split the amount of oil and water produced. Therefore, for the cores partially saturated with water, the recovery factors calculated are the total oil and water produced divided by the original oil and water saturated in the core. Results show that the recovery from the cores partially saturated with water was 17.34 % lower than that from the cores fully saturated with oil on the average for five cycles of N2 injection, and 45.15 % lower for three cycles of CO2 injection. In fact, these results show that the existing water will have a negative effect on oil recovery, indicating that increasing flow back of drilling and fracturing fluids will improve oil recovery. Moreover, the results show that the oil recovery factor from three cycles of CO2 injection was 36.33%, compared with 30.19% for five cycles of N2 injection. Likewise, the results confirmed that CO2 injection has higher oil recovery than N2 injection. Indeed, it is the first time to investigate the water saturation effect on oil recovery in the laboratory. The novelty of this experimental study is to demonstrate that the increasing flow back of drilling and fracturing fluids will improve oil recovery.