Exploitation of ultra-thin oil columns under gas cap and water support is challenging since both gas and water coning can seriously curtail oil recovery. Horizontal wells have shown to alleviate some of this problem as they allow for less drawdown and hence reduce coning for better recovery efficiency. Although the industry has shown horizontal drilling cost continues to be lowered, economics is still a major issue in exploiting ultra-thin oil bands using horizontal completion.

This paper presents a case study showing lessons learned from managing reservoirs with ultra-thin oil bands with less than 20 ft and sandwiched between gas cap and bottom/edge aquifer. Actual data from a field characterized by stacked pays of fluvial and deltaic channel sands in the Mahakam Delta complex are demonstrated. Subject to long-term production, the originally thick oil columns in these reservoirs have now become thinner, yet carry significant reserves to be prudently further developed. Issues involved in reservoir management such as well surveillance, well planning and prognosis, operating while drilling and producing, and long-term development plans are discussed. Reservoir modeling is shown to be the guide not only for well planning but also for well operations as it is used to select well type and completion strategy, optimize well production and prepare for continuous annual operating plan.

The vast well performance database provided from the paper shows horizontal drilling continues to be the main vehicle to develop these ultra-thin oil bands. Care however needs to be taken to scrutinize the economics inherent in selecting this type of completion, as other alternative methods also deserve to be considered.

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