The Definition and Manufacture of a Seawater Compatible Surfactant for an Offshore Chemical Enhanced Oil Recovery Pilot

Abstract

Experiences from a chemical supplier perspective are presented to define, optimize and manufacture a surfactant for use with seawater in an offshore enhanced oil recovery (EOR) test. This includes laboratory screening test results followed by quality control checks during manufacture. The surfactant concentrate was successfully manufactured, diluted with seawater, and injected as the main component of a surfactant-polymer (SP) formulation. A branched C12,13-alcohol-7PO-sulfate surfactant was designed for use with seawater. Particular pH buffer chemicals were screened for inclusion with the manufactured surfactant concentrate to give compatibility with seawater. The optimization of the surfactant concentrate with buffer included tests to assure acceptable aqueous solubility, storage stability and rheology. A quality control protocol was used that included decision gates with the operator and key stakeholders. Laboratory testing showed good aqueous solubility of the branched C12,13-alcohol-7PO-sulfate in seawater with about 3.5% TDS and 1800 ppm divalent ions (minor calcium and major magnesium ions). The pH buffer selected for this application gave a pH of 7 to 9 to: Prevent precipitation of Ca and Mg divalent cations that could otherwise lead to fluid injectivity issues, andKeep the pH stable and above 7 (preventing acid-catalyzed hydrolysis of the sulfate group) for good storage stability of the surfactant concentrate from time of manufacture to time of use. Ultimately, a 15% AM surfactant concentrate with Newtonian viscosity characteristics was manufactured and deployed due to transfer equipment handling requirements. However, for the future, concentrations of 70+% AM, also with Newtonian rheology, are possible for deployment. Implementation of the surfactants in EOR to date has been largely restricted to onshore applications due to the challenges associated with offshore use. This paper provides a real-world example of the manufacture of a surfactant concentrate that was used in an offshore SP field project from the perspective from a chemical supplier. Information relating to the quality assurance and control during surfactant concentrate upscaling is also critical and included in this paper.