Abstract

As part of the enhanced oil recovery (EOR) field development plan (FDP), four immiscible water alternating gas (iWAG) wells with intelligent well completions were successfully completed. Inflow control valves (ICV) with dual-permanent downhole gauges (PDG) in each zone were installed to allow remote injection control and monitoring. Each well has three zones. One of the iWAG wells was installed with the DTS cable behind casing. This enabled the injection profile monitoring across each sand in order to optimize the injection rate distribution and representatively amongst the four wells. The paper further discusses the injection strategy to meet the required zonal injectivity and reservoir zonal voidage replacement over field production life.

Downhole water injection conformance is critical for managing thin oil rim reservoirs. The injection plan considered several factors including uneven zonal split injection, short-circuiting injector to producer issues, and unfavourable zonal water-front propagation and changing injection scenarios over time. Hence, zonal control with optimal valve design is critical in achieving the EOR reservoir management plan. Injectivity and conformance modelling was performed on four iWAG wells across three reservoir zones to ensure optimal valve-sizing configuration for comingled injection multizone. A base case simulation assuming no downhole zonal control (all zones fully open) was first performed to understand the zonal injection performance and distribution contrast for both water and gas injection. This subsequently served as a guide for the zonal injectivity control strategy. This was followed by modelling valve sizes across a variety of injection scenarios. This was done to ensure the design working range for balancing future zonal injection selectivity under expected uncertainty range.

Post deployment ICV modelling was performed with cross-reference to actual petrophysical data, reservoir properties, and well trajectories. Petrophysical evaluation showed some zones are having lower permeability with low fracture pressure. Step rate injection test data was used to calibrate the model and to further validate whether the valve sizes were within the design ranges prior to the injection phase. Based on the simulation using surface injection rates and PDG pressure data, most of the zones were able to meet the target injection rate within the set fracture pressure. The model will then be further updated with the zonal injection data in the future as the iWAG injection program is implemented.

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