Enhanced Recovery Technologies for Unconventional Oil Reservoirs

Abstract

Management Unconventional resources have transformed the landscape of the oil and gas industry. The primary oil recovery factor ranges from 2–8% for the various shale plays throughout the US. Hence, it is imperative to develop the vast potential of unconventional reservoirs and increase the recovery factors beyond primary depletion by implementing IOR/EOR methods. This article describes the role of effective reservoir management and summarizes the detailed review of the advances in IOR/EOR technologies applied to unconventional oil reservoirs, as performed by the Energy Industry Partnership Team (EIP) at the University of Houston (Balasubramanian et al. 2018). That review•included: A thorough review of the pertinent published literature on IOR/EOR Results of EOR application to unconventionals shared by various operators in their investor presentations and from press reports Classifying IOR/EOR studies as laboratory experiments, numerical modeling, and field laboratory trials•(pilots) Analysis of field trials based on the representative shale plays. Most studies performed for the application of EOR technologies to unconventional oil reservoirs have been limited to experimental investigations and numerical simulation studies. The research revealed that miscible gas injection (produced field gases, CO2, etc.) is the most promising method among the EOR techniques, including miscible gas, waterflooding, surfactant, chemical, and polymer. Experimental studies showed the following: CO2 injection had the highest potential of improved recovery in unconventionals followed by produced gas injection. Surfactant injection showed the next best potential to increase oil recovery by altering the wettability of rock in laboratory experiments. The produced field gas injection pilots showed that sufficient injectivity was achieved mainly due to the injection-induced fractures and did not exhibit any significant effect of diffusion. Conformance control remains a big challenge due to the channeling of the gas through the fractures. Produced field gas injection pilots in the Eagle Ford formation have demonstrated the greatest success in increasing oil recovery. Many inconsistencies exist between laboratory investigations and field trials that need reconciliation and further research to bridge the gap. This methodical study elicits the learnings and challenges from the application of different IOR/EOR technologies to unconventionals at various scales (micro to macro to field scale). In addition, ideas for future research are recommended to improve the understanding of the complex mechanisms of EOR in unconventional oil reservoirs. Unconventional resources have changed the landscape of oil and gas industry in the US and the world. Oil production from unconventional tight oil reservoirs have accounted for more than 50% of total oil production in the US in the recent years. Todd et al. reported that unconventional oil reservoirs contributed to more than a 4 million•B/D increase in production between 2011 and•2014.