An investigation of factors affecting Low Tension Gas process for enhanced oil recovery in carbonate reservoirs

Laboratory scale experiments have established LTG (Low Tension Gas) flooding to be a promising EOR method in low permeability and high salinity carbonate reservoirs for both tertiary and secondary recovery. In this work, three important factors that strongly influence the performance of LTG process are investigated: (i) wettability, (ii) injection gas type, and salinity variation. LTG flooding was investigated for the first time for low permeability carbonate cores, which had been aged for over five weeks after being oil flooded at residual water saturation (aged cores), and high formation brine salinity hardness. Hydrocarbon gas from the field was tested as a candidate for co-injection with surfactant solution to generate foam during LTG flooding. This eliminates the need for importing gas from an external source. Another innovation in the LTG process design is that the need for freshwater or treating the produced water from the field was removed by using the re-purposed high salinity produced water for all stages of the LTG flood. LTG floods in aged cores was observed to give oil recovery similar to non-aged cores under same conditions. LTG flood in aged cores resulted in a residual oil saturation of 11% compared to 19.4% using secondary WAG injection.