CO2 Low Salinity Water Alternating Gas: A New Promising Approach for Enhanced Oil Recovery

Abstract

It has been recognized that there are significant advantages on combining low salinity waterflooding (LSW) with other enhanced oil recovery (EOR) techniques such as polymer or low tension surfactant flooding. This paper proposes a novel concept of low salinity water-alternating-CO 2 (CO 2 LSWAG) injection under CO 2 miscible displacement conditions. While LSW is an emerging EOR method based on alteration of wettability from oil-wet to water-wet conditions, WAG is a proven method for improving gas flooding performance by controlling the gas mobility. Therefore, LSWAG injection promotes the synergy of the mechanisms underlying these methods (i.e., ion-exchange, wettability alteration, and CO 2 miscible displacement and mobility control) that further enhances oil recovery and overcomes the late production problem frequently encountered in the conventional WAG. These features are demonstrated in this work based on a field case study. To investigate the advantages of CO 2 LSWAG, a comprehensive ion exchange model associated with geochemical processes has been developed and coupled to the multi-phase multi-component flow equations in an equation-of-state compositional simulator. Laboratory core flood simulations of different CO 2 LSWAG schemes are conducted to understand the combined effects of solubility of CO 2 in brine, dissolution of carbonate minerals, ion exchange, and wettability alteration. CO 2 LSWAG performance is then evaluated on a field scale through an innovative workflow that includes geological modeling, multiphase multi component reservoir flow modeling and process optimization. The simulation results indicate that CO 2 LSWAG has the highest oil recovery compared to conventional high salinity waterflood, high salinity WAG, and low salinity waterflood. A number of geological realizations are generated to assess the geological uncertainty effect, in particular clay distribution uncertainties, on CO 2 LSWAG efficiency. Finally, CO 2 LSWAG injection strategies are optimized by identifying key WAG parameters. The proposed workflow demonstrates the synergy between CO 2 WAG and LSW. Built in a robust reservoir simulator, it serves as a powerful tool for screening, design, optimization, and uncertainty assessment of the process performance from laboratory to and field scales. CO 2 LSWAG is a promising EOR technique as it not only combines the benefits of CO 2 injection and low salinity water floods but also promotes the synergy between these processes through the interactions between geochemical reactions associated with CO 2 injection, ion exchange process, and wettability alteration. This paper demonstrates the merits of this process through modeling, optimization and uncertainty assessment. IntroductionThe modification of the injected brine composition could improve the oil recovery factor of conventional waterflooding up to 38% (Web et al., 2004), leading to a new concept of optimal injection brine composition for waterflooding. Other than using high salinity reservoir water

Geochemical Interpretation and Field Scale Optimization of Low Salinity Water Flooding

“…Based on these premises, the novel concept of CO 2 low salinity Water-Alternating-Gas injection under CO 2 miscible displacement conditions has been proposed by Dang et al (2014). While LSW is emerging as an EOR method based on alteration of wettability from oil-wet to water-wet conditions, WAG is a proven method for improving gas flooding performance by controlling gas mobility.…”

Secondary Application of Low Salinity Waterflooding to Forties Sandstone Reservoirs

“…GEM has the additional ability to model enhanced low salinity processes such as the low salinity CO2 WAG process. (Dang et al 2014).…”

Hybrid CO2 EOR using polymer‐assisted carbonated low salinity waterflood to improve CO2 deliverability and mobility

“…A few hybrid EORs have investigated LSWF as a candidate to be implemented in the hybrid CO 2 EOR process . They use the CO 2 ‐WAG process.…”

“…investigated low‐salinity water alternating CO 2 flooding (LSCO 2 ‐WAG) through IFT and contact angle measurements and a core flooding test. Dang et al . numerically modeled the LSCO 2 ‐WAG process by considering both the geochemical reactions and EOS, and evaluated its synergetic effects.…”