- Copyright © 2004 Society of Exploration Geophysicists
Geologic models of hydrocarbon reservoirs are routinely used in the petroleum industry for volumetric calculation, well planning, and flow-performance prediction. A geologic model is a computer-based representation of the reservoir's architecture and properties. Properties such as porosity and lithofacies are estimated at each cell in a geologic model using various estimation methods; the most common are geostatistical simulation, such as sequential-Gaussian simulation and sequential-indicator simulation (Goovaerts, 1997), which take into account the spatial continuity of the property and also honor its heterogeneity.
For many reservoirs, wells may be sparse, and well data alone are often insufficient to adequately constrain the assignment of properties in the geologic model away from well control. Because most developments are under economic pressure to keep the well count at a minimum throughout the entire life of the field, 3D seismic data have been increasingly used to constrain the assignment of properties in the geologic model. This requires estimating these properties from the seismic data in the form of maps or volumes. However, there are issues associated with utilizing seismic data for this purpose, possibly the most important being that of the differences in scale and precision between the seismic and the well data.
Traditional geostatistical simulation methods designed to integrate the seismic data make some strong assumptions about the relationship between the coarse-scale seismic data and the fine-scale well data. Methods such as simple kriging with varying local means and collocated cokriging assume that the seismic data represent the same scale of information as the well data. Other approaches, such as block cokriging and simulated annealing, assume that the calibrated seismic data represent vertically averaged rock properties over a specified thickness of the reservoir. Some methods attempt to account for the imprecision of the seismic estimates by incorporating a term that is used to tolerate …