Unlocking Additional Production via Immiscible Water Alternate Gas (iWAG) Injection: Utilizing Free Flow Production Gas from Neighboring Field and Successful Switchover Execution Despite Possible Hydrate Threat
Authors: Abdul Rahman Nurul Haniza Binti , Raja Nazri Raja Nurul Hasif Bin , Daud Fairoz Irfan Bin 
Published: October 2023

Field B is a mature oilfield in offshore Sarawak with all wells being produced with gas lift and electrical submersible pumps (ESP). An Enhanced Oil Recovery (EOR) project was initiated to maximize economic value of the field utilizing immiscible Water Alternate Gas (iWAG) reservoir pressure maintenance method. Existing gas supply is insufficient to meet gas injection requirement and there is no water injection facility for iWAG requirement. This paper will cover the journey and challenges faced to enable iWAG implementation and approach taken to meet gas demand.

Integrated development of Field B with iWAG was implemented via four (4) injector wells, each of which will alternate between gas and water injection. Gas source supply for injection must be optimized including modification of nearby field Low Pressure (LP) separator to allow gas free flow to a new Central Processing Platform (CPP), which eventually eliminate continuous venting at nearby field. Revised Production Forecast post EOR has been analyzed to design a new CPP with adequate gas and liquid handling capacity to meet both the supply and demand for this integrated development.

Achieved first water and gas injection on April 2022, with all four (4) successfully completed its first switchover from Water to Gas (WTG) and Gas to Water (GTW) in November 2022. This was a result from the integrated and comprehensive switchover procedure which includes decision tree workflows and critical check lists to guide smooth switchover operation with corrective actions in-place. Complexities of narrow operating margin of operating conditions during start-up and switchover, which are close to the hydrate formation temperature is exacerbated by low landing temperature (due to seabed temperature) will increase risk of hydrate formation. To mitigate the hydrate formation risks, an electric heater is provided during WTG switchover operation. The hydrate formation risk is also applicable during GTW switchover as dehydrated injection gas becomes water saturated again when in contact with water in the wetted piping sections. To mitigate hydrate formation during GTW, methanol will be injected into the Water Injected (WI) stream while the Bullhead Pump works to evacuate the gas column in the well tubing. The gas evacuation strategy that enables free-flow export gas from nearby fields successfully complements the required gas demand into CPP compression facilities and eventually able to eliminate existing continuous venting at nearby fields.

This paper provides an insight into actual experiences in EOR field development utilizing iWAG technique, challenges in executing the switchover operation in view of reducing risks of hydrate formation and mitigation actions in-place. Maximizing the utilization of existing facilities and integrated gas evacuation strategy has guaranteed the gas supply and demand can be met. Significant value creation has been identified from additional production gain through iWAG as well as achieving zero continuous venting.