Capturing Matrix Uncertainties in a Giant Mature Carbonate Reservoir, North Oman

Hollis, Cathy¹, Harm Dijk¹, Simon Price¹, Mohammed Salhi¹, Ashwini Upadhyaya¹, Volker Vahrenkamp², Michiel Van Rijen¹, Lingli Wei¹ (1) Shell International Exploration and Production, Risjswijk, Netherlands (2) Petroleum Development Oman, Muscat, Oman

Many carbonate reservoirs in the Middle East are characterized by significant subsurface uncertainties due to strong heterogeneities in matrix flow units and fractures. One of the challenges to brownfield redevelopment of these reservoirs is the optimal use of historical data to identify and quantify those subsurface uncertainties that have impacted reservoir sweep. In addition, those parameters that may influence sweep efficiency under alternative future development options need to be assessed. The study area is a giant oil field in North Oman, in which the primary reservoir is the Natih Formation. Significant potential to improve the recovery factor for the field has been identified, and possible development options were screened using experimental design methods. This approach quantified the impact of static and dynamic elements by systematically mapping the combined effect of high uncertainty/high impact variables on hydrocarbon production. The study results show that although fractures exert a significant influence on productivity, it is also critical to under­stand heterogeneities in the matrix pore network in order optimize reservoir performance. In particular, variations in rock properties that result from sedimentological and diagenetic heterogeneities impart significant uncertainty in the prediction of sweep efficiency. Based on these results, the future work program can be better focused to constrain those parameters that most impact field performance, ensuring the future productivity of the field.