New Method for Reservoir Mapping

A map or, more generslly, a numerical model of an attribute’s dwhibution in spsce is rarely sn end goal. Maps are used as input to some transfer function designed to simulate a response of interest (Fig. 1). The “quslity” of a map m numericaf model should be appreciated in relation to the p2rticubu transfer function through which it will be processed. A map is a poor model of reality if it does not reflect those characteristics of the reaf spatial distribution that most affect the response function. The goaf of reservoir characterization is to provide a numerical model of reservoir attributes (porosity, permeability, saturations, etc.) for input into complex tmnsfer functions represented by the vtious flow simulators. The reservoir model is’ ‘good” if it provides response functions sidar to those that would be provided by a perfect model based on an exhaustive sampling of the rs.sewoir (see Fig. 1). Aspects of the resemoir that have little influence on the response of the flow-simulation exercise considered need not be modele~ however, reproduction of criticsl reservoir aspects is essential. Inmost flow simulations, the single most influential input is the permeabihw (or transmissivity) spatial distribution that conditions flow paths. 1,2 In a heterogeneous reservoir involving layers (e.g., shdes/sznds/fractures) with permeability values differing by several orders of magtimde, flow is conditioned primarily hy connected paths of high or low permeability values (flow paths and barriers, respectively). The hktograrn shape, whether log normal or not, and the proportions of extreme pemneabilby values do not matter as much as the spatiaf connectivity of these extreme vslues. Randomly disconnected small fractures mzy not generate flow paths, whereas a minute volume proportion of connected high pei’meabilhy vslues may control tlow and thus sweep efficiency and recovery. In such situations, reservoir charactetiation shotid detect patterns of connected extreme vslues and represent them in the numericsl model(s) to be