Potential of foam enhanced oil recovery process for a strongly oil-wet and heterogeneous carbonate reservoir

The feasibility of foam enhanced oil recovery (EOR) for a heterogeneous carbonate reservoir in the Middle East with medium temperature (55°C) and high formation salinity (above 16% TDS) is presented here. The promising surfactant formulations were firstly evaluated based on solubility tests and bulk foam tests. Afterwards, a series of core flooding experiments both in the absence and in the presence of crude oil were performed on Estaillades Limestone, a heterogeneous carbonate presenting reasonable similarities with the actual formation. In these foam tests, the influence of foam quality, injection velocity and surfactant concentration on foam strength and incremental oil recovery were investigated. Then, the lab results were reproduced by numerical simulation using a commercial reservoir simulator, where the model parameters were obtained after history matching. Finally, a synthetic 2D heterogeneous model was established to investigate how foam can assist in improving oil recovery for a stratified heterogeneous reservoir. An Alkyl Poly-Glycoside (APG) surfactant was firstly selected based on its prominent foamability and foam stability from bulk foam tests. The optimal foam quality is found to be around 70% from foam quality scan tests in the absence of crude oil. Moreover, foam still can be generated under strongly oil-wet conditions, and it is observed that the presence of oil and surfactant concentration have negligible effects on the optimal foam quality. However, the foam strength in high quality scheme is largely dependent on the surfactant concentrations. More than 20% OOIP of the water flooded residual oil was recovered after co-injecting 5.0 total pore volume (TPV) of nitrogen and 0.5 wt.% APG surfactant (in synthetic seawater brine) at 70% foam quality (4 ft./d). The numerical simulation results indicate that the permeability effect on foam strength and foam stability need to be considered in order to accurately model the foam behavior in heterogeneous reservoirs. In this presentation, the foam dry-out, shear thinning, surfactant concentration, permeability and oil saturation effects on foam transport in a heterogeneous carbonate were systematically investigated. The results of this study demonstrated the feasibility of foam EOR for a strongly oil-wet and heterogeneous carbonate reservoir with medium temperature and high formation salinity.