A Critical Review of Commingled and Stacked Reservoir Performances and Impact on Reservoir Management in Nigeria

Abstract

Abstract In many of the world's prolific hydrocarbon basins, multiple reservoirs are encountered stacked one above the other. Often, these stacked reservoirs are laterally extensive, each requiring multiple individual wells due to materiality in volumes and pattern of compartmentalization for proper and timely reservoir development. In Nigeria, the government regulations and good petroleum practices prescribe that the production of conventional oil and gas from distinct reservoirs or pools must be well accounted for good resource management and optimal reservoir development. Indeed, the development of commingled reservoirs and challenges of interval allocation remain a critical development concern. While most of these developments, present huge opportunity for accelerated reservoir exploitation, little or no review of the field performance evaluation for these reservoirs under commingled production are handy. To maximize the recovery of well penetrating through stacked reservoirs, most of the wells are usually with dual strings multi-zones selective completions. Commingling wells have historically provided an avenue to economically produce marginal reservoirs and production acceleration of multiple reservoirs through a single conduit when the conditions are deemed acceptable for reservoir management and volume recovery. These decisions are generally made with limited understanding of future well and reservoir performance. One of most famous challenges is trying to prevent early water or gas breakthrough. Another known challenge is failure of Interval Control Valves (ICV) or the intelligent completion systems, before the lifecycle of the reservoir, leading to early abandonment or production losses. More challenges like cross flow or pressure impact between zones, non-uniform flow from production zones and sand control issues are well-known challenges and these challenges individually present severe impact to the development objective. Of these development, equipment reliability issues and failures have been the key challenge to the lifecycle development of commingled smart wells. This performance review indicates a probability of survival after 5 years more than 96%. The extrapolated expected probability of survival after 10 years is more than 85%. This paper presents an in-depth review of actual well performances of commingled reservoir production in Nigeria. The paper also details the technical considerations required to reduce smart well completion failures and their impact on the reservoir management integrity and development objective. A guidance on the recovery factor benchmarks for productivity of intelligently completed wells, screening workflow and reservoir management strategies are presented. Finally, the paper highlights key performance and productivity indicators for smart well screening and selection for optimal reservoir management.