Application of Integrated Reservoir Studies and Techniques To Estimate Oil Volumes and Recovery—Tengiz Field, Republic of Kazakhstan

Summary Recent technical studies and probabilistic techniques have been integrated to build reservoir models for Tengiz field. Tengiz is one of the deepest supergiant oil fields in the world and is on the shore of the Caspian Sea within the Republic of Kazakhstan. Knowledge of the uncertainties inherent in oil recovery is a key to proper reservoir management of this important oil field. Probabilistic techniques gave insights into the importance and ranking of key reservoir uncertainties. This ranking is used to reduce reservoir uncertainties and to guide reservoir management activities. A structured Monte Carlo Technique has been used to construct several thousand static models of Tengiz field. Construction of Monte-Carlo models is fast and allows the impact of key uncertainties to be explored. Static reservoir uncertainties investigated include wireline log calibration, structural elevation, geostatistical parameters (such as variogram length), water saturation, and location of the boundary between facies intervals. Investigating the uncertainty in the dynamic performance of the model is computationally intensive. Experimental design techniques were used to minimize the number of computationally expensive simulation runs. Key dynamic variables investigated include: oil in place (OIP), gas/oil relative permeability, permeability enhancements, vertical-to-horizontal permeability ratio, well productivity, the water/oil contact (WOC) depth, and production capacity. The methodology for generating the range of possible outcomes for some development scenarios in Tengiz is discussed here. The application of Monte Carlo and experimental design techniques to identify the high impact static and dynamic parameters is reviewed. The construction of a probabilistic distribution of OIP and recoveries is demonstrated for one development alternative for Tengiz field. This study found that for this development alternative, the OIP, gas/oil relative permeability, and ratio of vertical to horizontal permeability have the greatest impact on the estimated oil recoveries.