Investigating effects of water on shale oil formation by using cyclic gas injection technique- an experimental study

In this paper, effects of water on shale recovery factor (RF) was investigated under different conditions experimentally. Some samples were saturated with oil at specific conditions. Other samples were partially saturated with water (NaCl), then saturated with oil. Then, number of cycles of N₂ and CO₂ injections were performed at fixed pressure, ambient temperature, and different operating conditions (e.g., soaking and production times). Results showed that as the number of cycles increased, RF also increased, and this increase depended on different parameters (e.g., soaking time). Results demonstrated increasing the soaking period results in higher RF. RFs of samples that were partially saturated with water were 17.34 % lower than RF of the base experiment by using N₂ injection and 45.15 % lower by using CO₂ injection. The RF achieved after conducting three cycles of CO₂ injection was 36.33%, 6.14% higher than RF after performing five cycles of N₂ injection. The results revealed that the efficacy of injecting CO₂ to produce fluid from the core samples is higher than N₂ at the same operating parameters. Results also demonstrated that presence of water has a negative impact on RF. Increasing flowback of drilling and fracturing fluids should be considered.