Extending the Applicability of Chemical EOR in High Salinity, High Temperature & Fractured Carbonate Reservoir Through Viscoelastic Surfactants

Abstract

Abstract Carbonate reservoirs possess the greatest challenge for chemical EOR methods. The challenges limiting the applicability of chemical EOR in carbonate reservoirs are the harsh reservoir conditions and the presence of fractures. Harsh conditions include high salinity, hardness and temperature. These conditions make most of the conventional surfactants and polymers ineffective. Fractures in carbonate reservoir provide the easy conduit for injected slugs to break through the production wells, thereby reducing the sweep efficiency drastically. Thus the carbonate reservoirs are not the best candidate for chemical EOR methods. Viscoelastic surfactant (VES) is the self-assembling surfactant that contributes to displacement and sweep efficiency through the formation of wormlike micelles (WLM). WLM can generate higher viscosity especially at the harsh conditions. The positive impact of VES towards salinity, hardness and temperature could favor its applicability as an EOR fluid. Elastic nature of VES could block the fractures. Three different Viscoelastic surfactants (Ethomin, Armovis and Aquadat) are screened based on WLM growth and IFT. The optimum VES is chosen then. The optimum VES is studied at various concentrations. Surfactants and polymers are added to VES forming S/VES and VES/P system. High Viscosity meant for mobility control and low IFT meant for oil mobilization are the two important parameters which any formulation in chemical EOR is desired for. Hence, ViscosistyIFT ratio of VES, S/VES and VES/P systems are studied individually with sea water of 57000 ppm at the temperature of 70°C. The potential formulation is reported. The potential of VES as the diversion fluid is also studied. Results indicated that Armovis could endure the harsh conditions among the three VES studied. VES system performs better followed by VES/P. VES can be a potential diversion agent.