ABSTRACT The objective of the work detailed was to develop an alkaline-surfactant-polymer (ASP) and achieve good oil recovery at low surfactant concentrations. A combination of phase behavior tests, interfacial tension (IFT) measurements (by spinning drop tensiometer) and coreflood tests were used to develop a solution for an oil that had an API gravity of 15 and viscosity of 2,000 cP.
The percentage of heavy oil in world oil production continues to rise as more light oil reservoirs have either depleted or reached their economic limit. However, the recovery factor from heavy oil reservoirs by both primary and secondary production is low, making these reservoirs candidates for chemical EOR technologies.
Phase behavior tests were used as the primary screening method to identify surfactant formulations qualitatively and the promising candidates were validated by IFT measurements (between the surfactant solution and oil) at different salinities to identify the lowest IFT formulation. Static adsorption tests with reservoir core material were used as a further screening step to ensure formulation was a viable option. Finally, linear coreflood tests were performed at reservoir temperature to validate the formulation and optimize chemical concentration. In one coreflood, 80% of waterflood residual oil was recovered using only 0.15% total surfactants and 2,000 ppm polymer.
The success of the ASP coreflood validates the ASP design for this heavy oil. Typically, heavy oil reservoirs may require lower surfactant concentrations due to higher permeability. As a result, such projects could potentially have a higher reward- risk ratio than ASP projects in conventional oil reservoirs.