Geomorphology: A Key to Filling Gaps and Increasing Realism in Reservoir Descriptions

R. S. Tye

Combining core and wireline data with geomorphic analogs facilitates the quantification of geologic information for the numerical characterization of subsurface strata. Traditional three-dimensional geologic descriptions are limited by one- and two-dimensional data sources (outcrop or well data). Geomorphic analyses of fluvio-deltaic systems reveal log-normal distributions of discrete depositional environments. These provide statistical constraints for conditioning the area (X and Y dimensions), shape, placement, and preferred orientation(s) of geologic facies in three-dimensional models.

Accurate stratigraphic and facies-association representations built from subsurface and analog data are integral parts of geologic modeling. Seismic, outcrop, and vertically oriented well data provide structural and chronostratigraphic information. Moreover, core and wireline-log data give lithofacies type and thickness (Z dimension), in addition to petrophysical trends. The distribution of facies in the X and Y directions (between wells) is realistically accomplished by using geomorphic guidelines to distribute lithofacies or facies- associations as three-dimensional objects. Furthermore, geomorphic analogs aid the distribution of a lithofacies within a facies association. This is beneficial where individual beds contain permeability extrema. Given a relationship between facies and p rmeability, a three-dimensional rendition of facies becomes a proxy for reservoir quality.

Geomorphic data from appropriate modern fluvio-deltaic analogs are linked with core and wireline-log data to render conditioned, three-dimensional, geologic models. Model accuracy relies upon bed-thickness and chronostratigraphic constraints imposed by cores and stratigraphic correlations, as well as, the lateral extent of facies associations governed by geomorphology.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California