Enhanced oil recovery (EOR) is a process for extracting oil that cannot be retrieved through the primary or secondary oil recovery techniques. A significant parameter that affects chemical (EOR) operations is chemical adsorption, which has a major impact on rock permeability, wettability, and the overall oil production.
Therefore, dynamic flooding experiments on an unconsolidated sand-pack model was conducted to investigate the chemical adsorption by calculating the amount of adsorption and the residual resistance factor at different injection conditions (injected chemical types and concentrations, salinity, temperature, flow rate, lithology and additive nano-silica). Two chemicals, i.e., bio-polymer (xanthan gum, XG), and anionic surfactant (sodium dodecylbenzene sulphonate, SDBS) were used as displacement fluids in sandstone formations.
Design Expert software was used to provide the number of experimental runs to each investigated factor, develop a predicted model for the amount of chemical adsorption and the residual resistance factor, and provide an optimum amount of chemical adsorption to enhance recovery.
The results showed that increasing the biopolymer concentration from 500 to 1500 ppm in sandstone formation at different injection conditions (flowrate from 2 to 6 ml/min, salinities ranging from 0 to 10 wt%, and temperature from 20◦C to 70◦C) resulted in increasing chemical adsorption from an initial value of 0.2 mg/g to 1.15 mg/g after stabilized condition of chemical adsorption. Similar trend was observed in case of SDBS such that increasing the surfactant concentration from 2000 ppm to 5000 ppm resulted in increasing adsorption from an initial value of 0.11mg/g to 1.07mg/g at the same injection conditions.
Using of nano-silica particles (NSP) as a co-injectant to the SDBS and XG enhanced the polymer adsorption by 67.8% and the surfactant adsorption by 60.2%. A previously proposed mechanism for the adsorption of XG/NSP and SDBS/NSP blends on sandstone was confirmed by the results obtained from the oil contact angle experiments. Finally, the adsorption optimization runs resulted in a recovery factor of 78.9% for the polymer folding, 67% for the surfactant, and 77% for the polymer-surfactant blend compared to 58% for the waterflooding base case.