Assessment of Foam for GOR Control to Optimize Miscible Gas Injection Recovery

Abstract

Abstract Miscible gas flood in a CEPSA-operated oil field has matured and, over the years, oil has been produced at an increasing gasoil ratio (GOR). Even though the gas displacement mechanism is miscible, or close to miscible, the poor mobility ratio between injected gas and displaced oil has led to inefficient sweep of the reservoir. The use of foam for gas mobility control is a proven IOR technology that can greatly improve gas injection conformance and hence improve volumetric sweep efficiency in secondary or tertiary recovery processes. This paper presents the results of comprehensive laboratory studies undertaken to define a foam system that will reduce gas mobility and preclude any risk of affecting formation injectivity. We evaluated four surfactants to establish the Foaminess, Mobility Reduction Factor (MRF) and impact of hardness, oil presence and surfactant concentration on foam strength: AOS C12-14 and AOS C14-16, LAS and Fluorobetaine. We found AOS C12-14 and AOS C14-16 to be the best foamers under screening conditions (60 bar, 90 °C): both significantly reduced mobility. AOS was not brine-sensitive but in the presence of oil, the foam performance was reduced. Optimum concentration regarding cost and effectiveness was found to be 5000 ppm. We demonstrated that strong foam can be formed under reservoir conditions (200 bar, 96 °C), using the Surfactant-Alternating-Gas injection technique. We have submitted a request for approval of a field pilot test which will be the first application of foam as an IOR technology in this field. If success is demonstrated in the field, the proposed approach should be helpful for field operators facing similar production optimization challenges or, for example, Foam-Assisted Water Alternating Gas (FAWAG) projects.