A review of chemical methods and testing techniques for enhanced oil recovery in shale reservoirs

In recent years, shale reservoirs have become increasingly important sources of oil and gas. As traditional methods of oil extraction reach their limits, there is a growing interest in exploring alternative techniques to enhance oil recovery from unconventional reservoirs, including shales. Various literature reviews have focused on enhanced oil recovery (EOR) in unconventional reservoirs. However, a comprehensive perspective specifically for shales that concentrates on chemical techniques remains scarce. This study evaluated several chemical strategies that demonstrate the potential of EOR from shales. Through a comprehensive review of these techniques, their feasibility and effectiveness were assessed. Furthermore, this work presents an overview of recent research aimed at enhancing oil recovery in shales using chemical methods. Additionally, it provides a comprehensive summary of current state-of-the-art techniques and their potential practical applications in the field. We identified areas that warrant further exploration, and demonstrated relevant field trials and pilot tests that are presently executed. Among other discussions, we show that the use of a hybrid method of chemical and gas combinations is effective for huff-n-puffs in shales. In addition, anionic surfactant formulations increase oil recovery in siliceous shales, whereas oil recovery increases for calcite-dominant shales using cationic surfactant formulations from different studies. Some studies have shown that the addition of nonionic surfactants to cationic and anionic surfactant solutions further increases oil recovery. Finally, we highlight that application of chemical techniques in shales has the potential to significantly increase oil recovery, provided that processes and procedures are continually refined through innovative research and development.