Enhancement of a Foaming Formulation with Zwitterionic Surfactants for GOR Control Application in Harsh Reservoir Conditions

Abstract

This work presents the development of an improved formulation based on an Alpha Olefin Sulfonate (AOS) as the main surfactant for in-situ foam generation. The need for this formulation enhancement is driven by the the harsh reservoir conditions of the presented case study, which push the surfactants to the limit and pose new challenges for foam EOR application. According to literature, anionic surfactants mixed with zwitterionic surfactants (such as betaines), possess strong interaction and profound synergistic effects for improving foam generation ability and foam stability. In this sense, betaines act as foam boosters and are able to expand the range of application of the main surfactants. Unfortunately, laboratory optimization procedures are not widely documented in the literature. Therefore, the aim of this paper is to delimit the applicability range of the AOS surfactant and to investigate its synergistic effects in mixtures with betaines to enhance foam performance. These are important steps to successfully design a robust formulation for a field pilot. For this purpose, we followed a laboratory workflow with a de-risking approach to define the most appropriate formulation for the challenging reservoir conditions of the presented case (high salinity, high divalent concentration, light oil, hydrocarbon gas and high temperature). The experiment setup was the following: Phase 1 defines the most appropriate base surfactant (AOS) among a series of commercial candidates. The negative impact of each variable (salinity, temperature and presence of light hydrocarbons) and differences between different AOS providers are addressed. Phase 2 defines the most appropriate betaine booster to be combined with the previously selected AOS and narrows the surfactant- booster ratio for enhanced synergistic effects in static conditions. Phase 3 optimizes the surfactant-booster ratio in a dynamic co-injection of the formulation, nitrogen gas and slugs of oil through a porous medium with similar characteristics to the reservoir rock. Phase 4 characterizes foam behavior according to critical variables (interstitial velocity, salinity, gas-water ratio) in coreflooding experiments using a core sample with live oil residual saturation. History matching allows to retrieve input parameters for the dynamic simulation. As a result of this study, a mixture of an AOS C14-C16 and cocamidopropyl hydroxysultaine (CAPHS) gave the best performance. The designed formulation has proved its robustness in a wide range of conditions, which will allow to generate strong foam at reservoir conditions and provide stable foam propagation, overcoming variations in salinity, concentration and gas-water ratio along the reservoir.