CO2 Soluble Surfactants Assisted Carbon Storage Under Achievable Pressure Gradients: Effect of Surfactant Partitioning Behavior During Continuous CO2 Injection

Abstract

Injecting CO2 into the saline aquifers normally suffers from low sweep efficiency due to the smaller density and viscosity of CO2 compared to brine. The potential of CO2 soluble surfactants assisted carbon storage in carbonate formations was first evaluated by core flooding tests (at 65°C, 150 bar & 90,000 TDS) in Indiana Limestone at different gas fractions, where the surfactants were injected with the CO2 phase (CCI+S). The pressure gradients and CO2 saturation were continuously monitored during the coreflooding tests. It was found that foam was generated during CCI+S when 0.07 wt.% of surfactant was injected with CO2. Moreover, the CO2 saturation at steady states can be significantly enhanced in the presence of foam from experimental observations. The CO2 saturation reached 60% (compared to 32% without surfactant) after 1.5 PV of CCI+S. The maximum pressure gradient was approximately 1.5 psi/ft in 162 mD Indiana Limestone at a Darcy velocity of 1.0 ft./d, which is technically feasible for field applications. Furthermore, an improved foam model incorporating the surfactant partitioning behavior was developed to obtain the foam modeling parameters by history matching the steady-state foam behavior. The effect of surfactant partition on CO2 transport behavior was studied by a 1D synthetic model at a lab scale and 2D synthetic homogeneous/heterogeneous models at the field scale, using modeling parameters and surfactant concentrations that are realistic for field tests. The sensitivity analyses imply that the CO2 storage efficiency largely depends on surfactant partitioning behavior (Ksgw), dispersivity, and formation heterogeneity, etc. The simulation results also indicate that there may always exist an optimal Ksgw for CCI+S, which satisfies both good CO2 sweep efficiency and acceptable injectivity. The advantages of injecting the surfactant with CO2 are more evident in heterogeneous saline aquifers, indicating an enormous potential of CCI+S for carbon storage. The novel injection strategy provides a promising solution for carbon sequestration in saline aquifers.