Evaluation of Surfactants for CO₂ Mobility Control in Dolomite Reservoirs

Laboratory studies were conducted to find the best surfactant for generating CO₂ foam in the presence of residual oil for two dolomite reservoirs. Conventional anionic and nonionic surfactants did not foam very well in core tests at reservoir conditions. The poor performance was attributed to the oil-wet nature of the dolomite cores. A new surfactant formulation was developed that alters wettability and has much better oil tolerance. CO₂ foams were generated easily with the new formulation and were more stable. Field tests are planned to demonstrate improvement of sweep efficiency using the new surfactant.

Evaluation of surfactants for mobility control applications involved a series of tests that measured brine compatibility, bench foam height, flow resistance in corefloods, and adsorption on reservoir rock. Bench foam tests, often used for surfactant screening, were unable to predict the effects of oil in the corefloods. Even the low oil saturation remaining after immiscible- or miscible CO₂ injection was detrimental to foam generation. The new surfactant formulation works over a wide range of brine salinities, controls CO₂ mobility better than conventional surfactants, and has moderately low adsorption on dolomite rock.