Development of in Situ CO₂ Generation Formulations for Enhanced Oil Recovery

Abstract

The carbon dioxide flooding of oil reservoirs represents one of the most-proven tertiary oil recovery practices. However, there are significant challenges associated with applying CO2 flooding in certain onshore or offshore fields and applications. The common challenges include a limited supply of CO2, transportation, capital cost investment, and corrosion. For offshore flooding, the critical challenge could be more related to extreme remote and significant project cost increase. In this work, we investigated delivering CO2 indirectly to the subsurface formation by injecting the concentrated solution of ammonium carbamate (AC) as CO2 generated species. Ammonium carbamate, a highly water soluble solid (40 wt %) and commercially available, can be dissolved in aqueous solution and injected to the reservoir where it decomposes at reservoir condition, thus releasing products of CO2 and ammonia. The produced CO2 results in lowering oil viscosity and oil swelling. Increase of ammonia concentration also lead to sand wettability reversal due to elevated alkalinity. Tertiary oil recovery performance of ammonium carbamate solution was evaluated by conducting multiple sand packs and core flooding test at various pressure and temperature conditions. Dodecane and several dead crude oils were used as oil phase. Injected AC concentrations tested were ranging from 5 to 35 wt %, with operational pressure, pressure (P) ranging from atmospheric to 4000 psi, and the preset temperature ranging from 96 to 133 °C. The average tertiary recovery observed from all the tests was found to be 29%. Results of laboratory experiments clearly demonstrated the potentials of this novel formulation for tertiary oil recovery. Mainly, it requires minimal capital investment up-front in comparison to CO2 flooding and largely eliminates the occurrence of gravity segregation and reduces adverse fingering behaviors because there is no presence of a free-CO2 phase involved. This endeavor serves as a successful proof of concept for the potential applications in tertiary oil recovery for both onshore and offshore fields.