In mature, multi layered reservoirs with commingled, dual string, and gravel packed completions, selecting reliable acid stimulation candidates has always been a challenge. Achieving a high success ratio under these conditions requires a risk-based selection process, supported by reservoir understanding and characterization.

As the traditional workflow, acid stimulation candidate selection starts with a thorough production performance review. Production history is provided on a string-by-string basis, and nodal analysis modeled based on production performance. Perforation and completions are evaluated to identify any damage. Logs are then reviewed to evaluate mineralogy and petrophysics. In this workflow, candidate selection is refined by reservoir modeling to predict the production gain in field level and production decline prediction. A decision and risk analysis is conducted with a strong emphasis on range of probability evaluates all possible outcomes associated with success and failure ratio. An economic analysis is evaluated based on risk analysis. This workflow is developed and tested in Bokor field, off the coast of Sarawak, Malaysia.

After acid stimulation campaigns spanning over 6 reservoirs, the results have yielded to 40% oil production gain. Six strings showed an increment in oil rate, a reduction in water cut and an increase in productivity. Overall, the fine tuned acid job design combined with visco-elastic surfactant diversion technique proved to be effective.

This paper presents the comprehensive workflow developed and implemented by the Bokor Project Management Team (BPMT) encompassing all the components necessary to deliver a risk based decision and therefore the optimum results.

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