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.
Water and gas injection are widely used techniques to alleviate pressure decline and improve sweep efficiency in brownfield reservoirs. When variable reservoir properties exist, such as permeability, pressure, and thickness, the requirements for real-time monitoring and control become crucial to ensure zonal injection target rates and volumes are achieved. The Bokor Field is located in the Baram Delta area of the South China Sea, 45 km from the shore of Sarawak, Malaysia, in a water depth of approximately 70 m. This marks the initial use in Malaysia of a distributed temperature sensing (DTS) fiber optic cable installed and cemented behind casing in a multizone immiscible water alternating gas (IWAG) injection well. Injection profiling was monitored via the DTS across multistacked reservoirs having different horizontal permeabilities. The DTS detected injection profile patterns within each zone and enabled identification of high permeability streaks and thief zones. Inflow control valves (ICV) were then used for injection management and control. For Bokor well, offshore Malaysia, an intelligent completion system was chosen. The well comprised downhole flow control valves with 8 choke positions, permanent downhole gauges, and a DTS cable to enable optimum injection conformance. DTS provides real-time temperature measurements along a multimode optical fiber encased in a ¼-in control line. Enhanced measurement accuracy can be achieved by placing the DTS cable as close as possible to the reservoir by installing it behind the production casing in direct contact with the reservoir formation. Deployment of the DTS in such a way presents several challenges in the design and operational phases. The first challenge is to ensure the integrity of the cable while running and cementing the casing in a highly deviated trajectory. Special equipment was designed to ensure mechanical protection of the fiber while safeguarding the quality of the cement-to-casing bond. An innovative TCP perforating technique and cable detection system had to be developed to prevent damage to the DTS when perforating the casing. Several design interfaces and system integration tests were identified and carried out between multiple providers to guarantee a smooth and successful installation. Preliminary results demonstrate intelligent technology for real-time monitoring of the actual injection profile behind casing, and for controlling it remotely via an RTAC (real-time acquisition and control) software solution.
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