IOR Methods in Unconventional Reservoirs of North America: Comprehensive Review

Abstract

Abstract Unconventional resources have played a significant role in changing oil industry plans recently. Shale formations in North America have huge oil in place, 900 Billion barrels of recoverable oil in Bakken only. However, the predicted primary recovery is still low as less than 10%. Therefore, seeking for improved oil techniques to increase oil recovery in these complex plays is inevitable. In this paper, three stages of review have been combined to find out the applicability of the most feasible IOR methods in these unconventional reservoirs. Firstly, the most common fluid and rock properties of these reservoirs have been investigated and extensively discussed. Secondly, a comprehensive review has been conducted on most of published experimental studies, simulation works, and pilot tests which were performed to examine the applicability of different IOR methods in these unconventional plays. Finally, the performance of different IOR methods in pilots tests have been compared with experimental and simulation observations. These comparisons between field scale approaches (Pilot tests) and lab experiments have been used to diagnose the gap beween what had been reported from lab works and what happened in the field tests. This study found the integration method of different tools such as experimental, simulation, and pilot tests is the proper technique to accurately diagnose the most feasible IOR methods in these poor-quality reservoirs. This research found that CO2, surfactant, and natural gas are the most applicable IOR methods in these unconventional reservoirs. CO2 injection seems the most feasible technique among the reported IOR methods. However, this study found that there is a clear gap between lab-works conclusions and pilot tests performance. This gap mainly happened due to the misleading predicting for that diffusion mechanism would be the most dominant mechanism for CO2 in field conditions due to the pre-reported lab observations. However, pilot tests performance generaly denied any significant role for diffusion mechanisim on CO2 performance. Furthermore, although pilot tests indicated that injectivity problem is not a big obstacle in these unconventional reservoirs, most of the evidences explained that the improvement in the observed injectivity was due to Injection Induced Fractures (IIF) which are the main reason for conformance problems which happened in the reported pilot tests. The slow imbibition rate of surfacatant methods in these types of reservoirs might impair their potentinal success. Pilot tests apparently approved success of natural gas due its high compressibility and avialbility in these fields. Finally, this work specifies the most common problems which could face the most potentional unconventional IOR methods in field applications. Also, this study recommended new directions to be considered for fututure investigations on applicability of some IOR methods in these plays since they are more complex and very different from conventional formations.