Complex Multi-Stacked Reservoir Development – A Successful Case Study Offshore Gulf of Thailand

Abstract Many fields in the Gulf of Thailand (GoT) consist of multi-stacked reservoirs with various degrees of aquifer strengths and varying reservoir properties. Commingled production with sand control has been challenging due to productivity loss from sand failure, and/or early water breakthrough. This case study demonstrates how a combination of integrated reservoir simulation and out-of-the-box well completion designs were used to enhance recovery and economically develop an otherwise marginal 1500 ft. long small multi-stacked reservoir offshore GoT. Separate static and dynamic models existed for two of the four reservoirs of interest. A pre-drill study amalgamated the static models into a single stacked model in readiness for a multizone commingled flow study. A high-resolution numerical simulation model was then created, integrating varying rock properties and aquifer strengths observed from historical data. The completion strategy sought to isolate multiple water bearing zones straddling the hydrocarbon zones with swell packers and integrate inflow control to manage the variability in reservoir properties and aquifer sizes. A real-time update of the pre-drill model was required to best optimize the inflow control device (ICD) design. During the campaign, multiple additional oil-bearing reservoirs were discovered. The team quickly updated the geological models and generated fit-for-purpose high resolution dynamic simulation models, building in multiple scenarios with more than a million active grid cells, to best reflect the understanding of the new reservoirs. This was done within the very short time permitted by operational constraints and helped increase the confidence in ICD nozzle sizing. The reservoir drilling fluids had to be modified to ensure a good swell packer performance for zonal isolation integrity. A total of 8 sands were completed in this well, from 4 originally planned. Post-drill production performance from the well suggests a strong conformance to the pre-drill models as far as inflow goes. The benefit of the ICD deployed in this highly deviated well was demonstrated, with the smaller nozzle sizes limiting inflow from zones with higher productivities and quicker water breakthroughs. The swell packers performed very well judging from the water cut profile from the well. A similar approach is planned to be used in multiple other marginal multi-stacked oil reservoir in this field and others. This study demonstrates what is possible when different areas of expertise work together to combine/integrate multiple separate existing technologies. High resolution numerical simulation was combined with sand control and inflow control technologies with modified drilling fluids and swell packer designs to make the development of these otherwise uneconomic multi-stacked marginal reservoirs possible.