Geostatistical analysis of 3C-3D seismic data for depth, isopachs, and sand/shale distribution
Todor I. Todorov, Robert R. Stewart
Three examples of applying geostatistical methods in the Blackfoot area, Alberta, are shown. The examples include time-to-depth conversion, isopach estimation, and sand/shale determination. Conventional time-to-depth conversion requires a correct velocity model, which is often difficult to obtain. Using well depths and two-way traveltimes to the Mannville horizon, a cokriging depth structure map is generated. The estimated Mannville depth in the area varies from 1480m. to 1520m. Cross validation test is used to evaluate the result and shows a very small absolute error in the range of -3.30m. to 2m. In a similar fashion an isopach map for the Mannville - Mississippian is obtained showing an interval thickness from 160m. to 200m. Thecross-validation absolute error is from -13 m. to -4.5m. Gamma ray logs are used to deduce the shale content at the well locations. An average Vp/Vs map is used as a second variable in the cokriging estimation and a sand/shale distribution map is generated. The shale content varies from less than 35% in the producing area to over 50% in the dry wells area. For the three examples, fifty Gaussian simulations are performed. The average maps show very similar features with the cokriging results.