Laboratory Investigation of a Novel Hybrid Surfactant-Gas Enhanced Oil Recovery for Tight Oil Reservoirs

Abstract

Enhanced oil recovery in unconventional reservoirs is gaining momentum. Many operators are commercially implementing gas injection enhanced oil recovery in their shale assets, using carbon dioxide (CO2) or enriched hydrocarbon gas. The injected gas produces oil through oil swelling and vaporization. Recently, surfactant-based enhanced oil recovery (EOR) is being considered for improving recovery in unconventional reservoirs. This study is a proof of concept of applying a combined surfactant and gas injection EOR to shale reservoirs. In this study, a combination of surfactant assisted spontaneous imbibition (SASI) and CO2 injection in a silica-rich tight oil-wet rock representing shale reservoir conditions is investigated. The core flood experiments were conducted on tight Scioto core plugs with micro-darcy permeability. The core plugs were saturated and aged in Bakken and Eagle Ford oil. The surfactants (nonionic, cationic, and anionic) were delineated based on contact angle, IFT measurements, and spontaneous imbibition experiments prior to conducting core flood experiments. The core flood experiments show an additional oil recovery by gas injection over the high initial recovery by surfactant imbibition, irrespective of the type of surfactant used. There is at least an additional 2.8% recovery by gas injection which followed the initial high recovery of at least 50% by surfactants.