DESIGN AND APPLICATION OF A NEW ACID-ALKALI- POLYMERIC SURFACTANT FLOODING FORMULATION FOR ENHANCED OIL RECOVERY

In this study, new chemical flooding formulations have been developed to overcome the precipitation problems caused by the divalent metal cations prevalent with conventional ASP flooding. The purpose of the new design was to make an economical and effective chemical flooding project using natural sea water. To accomplish this objective, this research work was divided into two parts. In the first part, a series of new polymeric surfactants (PS) were produced by the sulfonation and polymerization of methyl esters derived from non-edible Jatropha oil. The PS was designed to graft the sulfonated group to the polymer backbone as one component system for interfacial tension (IFT) reduction and viscosity control. In the second part, two chemical formulations were developed using the screened PS. The first formula consists of acid-alkali-polymeric surfactant (AAPS) and second formula consists of alkali and polymeric surfactant (APS). The AAPS formula was aimed to overcome the precipitation problems using natural sea water. The second formula was developed to simulate the conventional ASP flooding and also to examine the performance of the polymeric surfactant with alkali using softened water. A comprehensive approach has been taken to study the feasibility of the new formulas with the produced PS. The approach included fluid-fluid interaction tests, interfacial tension measurements, phase behavior tests, and, surfactant adsorption tests, and physical simulation using Berea core samples. The purpose of these tests was to establish the optimum chemicals concentrations for Angsi crude oil and to determine the technical feasibility and the injection strategy of the proposed formulas.
As results of various experiments, the polymeric surfactant showed an excellent performance for IFT reduction and viscosity control with Angsi crude oil. The compatibility tests showed that all alkali employed were not compatible with either sea or softened water. However, the acid effectively prevented calcium and magnesium precipitations and all solutions remained clear in the presence of sea water maintained for 90 days at 90oC. A combination of alkali and surfactant was found to significantly reduce the IFT and surfactant adsorption with the use of softened water. The IFT measurements indicated an increase in the IFT as the acid concentrations increased with either surfactant or alkali, despite a slight decrease on the IFT when the three components were combined. It is of note that the viscosity of the AAPS solutions increased in the presence of the alkali and remained constant when the alkali concentration was as high as 0.2-1.2 wt%.
Based on series of core flood tests, the optimum chemicals concentrations were found to be 0.99% acid, 0.6% alkali, 0.6% polymeric surfactant for the usage of sea water and 0.8% alkali, 0.6% polymeric surfactant for the softened water. Injection of 0.5PV of the formulated AAPS slug followed by chase water produced an additional 18.8% OOIP. Meanwhile, 16.3% OOIP was recovered when 0.5PV of the formulated APS slug was injected and followed by extend water flood. The benefit of the new system is the use of sea water rather than softened water while maintaining the desired slug properties. This makes the new AAPS formula an attractive and cost-effective agent for chemical EOR particularly for offshore field application.