New Methodology for Estimation and Sensitivity Testing of STOOIP in Carbonate Reservoirs: The Pore-type Concept

Traditional methods for estimating STOOIP (Stock Tank Original Oil In Place) is based on the use of average input parameters for different reservoir zones, and by the application of a variety of cut-offs in net-to gross evaluations. This methodology creates a significant uncertainty in the STOOIP calculation, especially related to saturation and to the application of cut-offs. A new methodology has been developed for estimating matrix-related STOOIP and for predicting the sensitivity of the estimates. This method does not apply fixed input parameters, but uses measured and/or predicted, pore-type related input parameters that vary continuously through the reservoir. Well data are normally preferred as input data, although it is possible to use data from geological models. The methodology is to a large degree based on pore-type control of reservoir parameters. The new methodology has been applied to a Middle East oil field, and STOOIP estimates are significantly different to those obtained from traditional methodology.