Enhanced Oil Recovery in Carbonate Reservoirs Using Single Component Synthesized Surfactants under Harsh Reservoir Conditions

Surfactantsare commonly used for enhanced oil recovery(EOR) applicationsin carbonate hydrocarbon reservoirs due to their ability to reduceoil/water interfacial tension (IFT) and/or alter rock wettabilitytoward more water-wet conditions. They are usually used as formulationsconsisting of more than two surfactants to achieve optimum performance.Although this approach may result in extra recovery in corefloodingexperiments, there is a risk of chromatographic separation and potentialphase separation when these surfactants are injected into the reservoir.The current study, however, focuses on injecting a single componentethoxylated quaternary ammonium cationic Gemini surfactant (GS) ora betaine-type zwitterionic surfactant (ZIS), both synthesized in-house,to mitigate these potential issues. Several coreflooding experimentswere conducted using Indiana limestone samples at 100 & DEG;C, pressuresgreater than 3000 psi, and seawater and formation water salinitiesof 57,745 ppm and 213,768, respectively. Continuous injection of eithersurfactant solution (at 2500 ppm in seawater) after seawater floodingrecovered almost 11-12% of the initial oil in the core (OOIP).The results demonstrate that the GS or the ZIS alone can achieve thisrelatively high oil recovery without the need for additional cosolvent(s)or cosurfactant(s), unlike most of the previously developed surfactantformulations. Injecting a one-pore-volume slug of a standard acrylamidecopolymer at 2000 ppm between the seawater and the surfactant floodsincreased the oil recovery by either surfactant to around 16-17%OOIP. This improvement in oil recovery was mainly due to wettabilityalteration from oil-wet to intermediate-wet conditions, as revealedby the contact angle and oil/water IFT measurements. Effluent analysisof the produced aqueous phase showed surfactant dynamic retentionvalues of 0.44 and 0.61 mg/g-rock of both the GS and the ZIS, respectively.Such high oil recovery and low dynamic retention reflect the highefficiency of the GS and the ZIS for EOR applications in carbonatereservoirs.

Automated summary

Surfactants are commonly used in carbonate hydrocarbon reservoirs for enhanced oil recovery. This study focuses on injecting a single component surfactant to mitigate the risk of chromatographic and phase separation. The results show that the single component surfactant alone can achieve high oil recovery without the need for additional cosolvents or cosurfactants, and injecting a polymer can further improve the oil recovery.