Feasibility Study of Low-Tension-Gas Flooding Application in High Temperature High Salinity Sandstone Reservoirs

Abstract

Abstract Low-tension-gas (LTG) flooding has been demonstrated in the laboratory to improve oil recovery for tight formations with sub-20-md permeability. High temperature and high salinity (HTHS) reservoir conditions still pose significant challenges for this hybrid surfactant and gas enhance oil recovery (EOR) method. This paper presents a systematic study that includes developing low interfacial tension (IFT) surfactant formulation, investigating LTG flooding, and lab-scale reservoir simulations to evaluate the feasibility of LTG for field application in harsh reservoir conditions. The brine and crude oil analysis showed that the formation water and injection water from the interested field have total dissolved solids (TDS) up to 70,000 ppm and divalent cations, such as calcium (Ca2+) and magnesium (Mg2+) over 2,000 ppm, and the crude oil contains over 5% asphaltene and has total acid number of > 0.5 mg KOH/g. A novel synergistic blend of two commercially available long-alkyl-chain surfactants with a co-solvent was developed with ultralow IFT and acceptable foamability at 92°C. The foam injectivity core flood showed that a foam quality of 50-80% demonstrated a stable foam. The surfactant polymer (SP) core flood test using outcrop cores demonstrated the efficiency of the developed ultra-low IFT surfactant formulation. LTG core flood experiments using reservoir core plugs were performed by injecting the same low tension surfactant formulation along with gas at 50% quality followed by foam drive with the mobility control foam at 80% quality. The residual oil saturation was reduced to less than 5% by LTG flooding. The lab observed recovery was accurately modeled using UTCHEM, a chemical flooding simulator. Our experimental work demonstrates the effectiveness of LTG flooding in high temperature sandstone reservoirs with high divalent cations in high salinity formation brine. Our mechanistic models and numerical simulations for this complex surfactant and gas EOR method matched the experimental results.