Reservoir Characterization Using Expert Knowledge, Data and Statistics- Disk 2

January 1992 The simplest representation of a reservoir is a homogeneous tank with uniform properties throughout. Characterizing such a simplified model requires merely enough data to define its volume and basic petrophysical properties. This information can then be used to help forecast reservoir behavior and compare possible production scenarios. But efficient exploitation of reserves requires a more sophisticated approach. Reservoirs have been created by complex sedimentary and diagenetic processes, and modified by a history of tectonic change. Rather than resembling simple tanks, reservoirs are heterogeneous structures at every scale. The need for accurate characterization is vital for oil company economic planning (next page, top). In the past, geologists have used expert knowledge to interpolate between wells and produce basic reservoir models. However, during the last ten years, this effort has been transformed by statistical modeling offering insight into the effects of heterogeneity. This article details how reservoir descriptions are developed and is divided into three stages (page 27): •Defining the reservoir’s large-scale structure using deterministic data •Defining the small-scale structure using statistical techniques—geostatistics •Rescaling the detailed geologic model to be suitable input for a fluid-flow simulator.