Chromatographic Separation of Chemicals in Alkaline Surfactant Polymer Flooding in Reservoir Rocks in the Daqing Oilfield

Abstract

Abstract Alkaline-surfactant-polymer (ASP) flooding have been studied and applied in Daqing oil field for more than 15 years, where eight ASP pilot tests of different scales had been conducted and five ASP foods have been pilot tested. Incremental recoveries are from 19.4 to 25%(OOIP). Since the adsorption of each chemical component would have significant impact on the cost-effective and recovery efficiency of the ASP flooding process, laboratory experiments were conducted to investigate the adsorption of each component in reservoir rocks as well as the analysis of the mineral contents and the clay compositions in the reservoir rock taking from the ASP test area in the Daqing Oilfield. In the adsorption study, four chemicals; a surfactant, an alkaline agent, polymers, and a sacrificial agent were used. The results showed that the adsorption of surfactant does not obey the Langmuir adsorption isotherm and has a maximum value of 0.6 mg/m2, but adsorptions of alkali and polymer chemicals do obey the Langmuir adsorption isotherm. Adsorption tests also indicated that the adsorption of surfactant could be reduced by 30% with the addition of 0.15wt% of a bio-surfactant as a sacrificial agent into the key surfactant, ORS-41, solution. In addition to adsorption tests, retention (dynamic adsorption) tests were conducted using reservoir core plugs. The results showed that the sequences and peaks of relative concentration (C/C0) of chemicals in effluent are polymer, alkali, and then surfactant. The results also showed that the adsorption of the surfactant is the greatest among all chemicals. This phenomenon indicates the chromatographic separation of three chemicals transport process in cores. The chemical analysis and the chromatographic separation of these chemicals in produced fluids the previous three pilot tests showed consistent results with laboratory studies, and the degree of retention of the surfactant is proportional to the clay content in field tests. Based on these findings, an ASP flooding pilot test was conducted in the Daqing Oilfield in 1994 with the combination of a bio-surfactant and the key surfactant, ORS-41. Since the adsorption of the bio-surfactant is stronger than ORS-41, the bio-surfactant was used in the ASP pilot test to lower the amount of the more expensive ORS-41. However, the effect of bio-surfactant as sacrificial agent on chromatographic separation of chemicals in ASP flooding (or surfactant lag) is not obvious.