Experimental evaluation of foam for mobility control in water alternating gas enhanced oil recovery in a Middle Eastern carbonate reservoir

Various enhanced oil recovery methods (EOR) suffer from poor sweep efficiency due to viscous fingering, channeling, and gravity segregation issues. The water-alternating-gas method (WAG) used in the Al-Shaheen’s Shuaiba reservoir has encountered similar problems, whereby injected gas preferentially flows into higher permeability zones and sweep efficiency is impacted. The goal of this research work was to develop an effective, and economically viable foam system that can utilize waste gas in the Al-Shaheen reservoir as a mobility control solution. This research focused on an optimized surfactant formulation that can generate foam with methane gas at the reservoir conditions in the presence of oil and an oil wet/mixed wet rock. The formulation was tested in water wet and oil wet core flood experiments. Enhancements to the formulation were tested and their improvement to the foam strength was quantified. An anionic surfactant group alkyl-polyglycoside (APG) was first chosen through screening experiments. The bulk foam stability was then evaluated with and without oil presence and showed APG-5 as the best among the APGs. Its adsorption to carbonate Estaillades limestone was estimated around 2.5 mg/g of rock at 55 °C and the reservoir brine salinity of 144,000 ppm. Core flood experiments revealed that a concentration of 3500 ppm is required to achieve strong foam. The foam rheology of APG-5 and methane gas was found to be shear thinning. The ideal foam quality resulting in the strongest foam was found to be between 30 and 50 %. The impact of oil on the APG-5 foam was studied, and found to produce effective foam in presence of residual oil in water wet cores and oil wet cores, with mobility reduction factor (MRF) values of 28 for the former and 24 for the latter. It was also shown through mobile oil experiments that foam can develop even in presence of mobile oil. Oil wet environments were shown to have weaker foams. The use of a wettability altering agent TGT-1 improved the foam propagation and steady state strength. MRF values of ~ 47 were achieved, an increase of 150%. A foam booster (Lauryl Betaine) was tested and found to enhance the propagation and steady state strength of the foam with MRF values of 52. Combining the wettability alteration, and foam boosting in a final formulation achieved and MRF of 85