Low-tension gas process in high-salinity and low-permeability reservoirs

Abstract

Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging, as well as high-pressure gradients in these reservoirs. Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine. Low-tension gas (LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity. In LTG flooding, the interfacial tension between oil and water is reduced to ultra-low values (10−3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood. Gas (nitrogen, hydrocarbon gases or CO2) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced (oil) and displacing phases, thus improving the displacement efficiency of the oil. In this work, the mechanism governing LTG flooding in low-permeability, high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments. The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality, and how they influence oil mobilization and displacement efficiency. Qualitative assessment of the results was performed by studying oil recovery, oil fractional flow, oil bank breakthrough and effluent salinity and pressure drop characteristics.

Impact of Injection Gas on Low-Tension Foam Process for EOR in Low-Permeability Oil-Wet Carbonates

“…The entire slug is 0.3 LPV, meaning that by the time 1 PV of total injection was reached, only 67% of the slug had been injected. This would also contribute to the poor oil recovery at 1 PV of total injected fluid, since not all the desired amount of surfactant in the slug was injected [30].…”

Technical Evaluation of Conformance Improvement Technology with Anionic Surfactant-Stabilized Microemulsions in Porous Media

“…Microemulsion-assisted conformance improvement technology (ME-CIT) is based on the cyclic injection of microemulsion/surfactant slugs in surface conditions and sufficient viscosity within the targeted pore regions (Das et al, 2020;Quintero et al, 2015;. It relies on two important attributes: stability and viscosity (Divandari et al, 2021;Sagbana and Abushaikha, 2021;X.…”