Improved Reservoir Management Practice Using Reservoir Performance Indicator Based On the Dynamic Model Uncertainty Study

Abstract

At first, the risk assessment of dynamic model parameters based on uncertainty analysis was conducted to evaluate the impact of the reservoir uncertainties in a carbonate reservoir, offshore Abu Dhabi. The study showed that the evolution of gas to oil ratio (GOR) was a main reservoir response that affected the future production profile; hence it is the focus of this paper. It is important to track the GOR behavior in the field, to compare the actual reservoir performance with the risk assessment results and to evaluate the proper reservoir management and development options. Uncertainty analysis was used to evaluate future GOR performance and its probability of occurrence. The range of production plateau duration was also quantified. Therefore, future GOR performance impact on production for all probability ranges can be estimated. Finally, "GOR performance indicator" was developed by use of GOR upside and downside performance curves generated as a result of uncertainty studies. More than three years of monitoring GOR evolution by use of the developed GOR performance indicator allows the assessment of GOR behavior trends against the expected performance, which permits the development of adequate reservoir management plans. The GOR trend can be explained as a result of reservoir management actions such as optimizing gas injection rate, adjusting well production rate and closing high GOR (HGOR) oil producers. Accordingly, the GOR trend can indicate the current reservoir performance compared to the range of uncertainty analysis. It also can put light on required reservoir management action plans for operations and assist building assurance of the reservoir development. Consequently, the developed "GOR performance indicator" is based on the reservoir simulation outputs for uncertainty analysis. In case that the GOR trend is deviating from the range of the GOR performance indicator, the reservoir simulation inputs needs to be modified. The developed GOR performance indicator is considered useful to foresee required reservoir management action plans and to suggest alternative development plan needs in case of unfavorable actual reservoir performance. It is noted that the GOR performance indicator can be updated based on new information available. Additional data gathering can support to narrow uncertainty ranges.