Polymer Field Development with a Strong Bottom-Up Aquifer in a Field in the South of the Sultanate of Oman

Abstract

Full field polymer flood has been identified as a potential EOR process for a heavy oil field with a strong bottom aquifer in the South of the Sultanate of Oman. A number of surface and subsurface risks have been identified prior to field implementation, including matrix injectivity, polymer sweep and impact of back produced polymer on surface facility & the field wet lands (reed beds). The development of the field will take a place in a phased manner in order to reduce the capex exposure, maximize the utilization of existing facility and managing project risks while contributing to the overall production. In order to support the standardization and steer the future phases the modular facility concept was selected as basis for polymer preparation and injection facilities, this design was made flexible enough to cater for a wide range of possible trial outcomes. A very comprehensive polymer pilot was performed in this dome-shaped heavy oil reservoir to assess polymer sweep performance as well as losses to the strong water aquifer. An inclusive real-time surveillance programme was executed to monitor key parameters including pressure, injection/production rates, viscosity and water quality, which concluded incremental oil gain from the process. Other tests were conducted to assess the impact of back produced polymer on growth of plants, heater fouling and surface facility separation tanks. In general, all results were positive which paved the way for field-wide development of polymer flooding with less Capex requirement. A sustained incremental oil gain was clearly observed from polymer injection, which was supported by saturation logs acquired from the observation wells. Injectivity could not be maintained as planned, due to a combination of polymer, biological and water quality issues. Later tests including biocide injection and QA/QC of polymer batches as well as some well stimulation did show improved injectivity profiles. Demulsifier tests mitigated the risk of creating stable emulsions. Lab tests indicated no heater fouling observed below 150°Cdeg. Short and long term investigation into the impact of water-contaminated polymer on plants in the wet lands was positive with the plants showing no necrosis with back produced polymer concentrations up to 500 ppm which is achievable given the excessive amount of water received at the facility level that dilute the back produced polymer. This helped in making the project more economically attractive as it results of a saving of around 30% from the overall project Capex. The different surface and subsurface tests paved the way for a full field implementation of polymer injection in structures with strong bottom water aquifer. The paper discusses the phasing that was purused to mitigate risks, learn on the go and improve the project economics