Print this pageCrosswell Seismic Data from a Carbonate Reservoir - Geologic Investigation and Implications for Reservoir Characterization
TUCKER, KARLA E., PAUL M. HARRIS, and RICHARD C. NOLEN-HOEKSEMA
Data from McElroy field, a West Texas carbonate reservoir, illustrate:
1. The vertical resolution of crosswell seismic data from a geologic perspective -- As a result of ubiquitous cementation by gypsum and anhydrite, whole-core porosity and permeability are highly variable over the main pay interval and are not obviously related to core-based lithofacies. Total porosity and mineralogy influence crosswell velocity, as shown by acoustic measurements on plug samples, and the relationship between S-wave reflections and decreases in whole-core porosity and/or gypsum cement. Because log and crosswell data are responding to the same diagenetic overprint, we group log data into logfacies using cluster analysis for correlating reservoir flow units and relating them to the crosswell images. S-wave reflections generally correspond to transitions between "best" reservoir and less porous reservoir clusters.
2. The lateral variation of porosity suggested by crosswell seismic data -- Cross-section models facilitate a comparison between lateral variations of porosity and S-wave amplitudes. Geostatistically generated logfacies cross-sections represent porosity groupings with lateral transitions corresponding to variations along many positive amplitude events. Although detailed variation (resolution) in the porosity models is probably much greater than the resolution of the S-wave images, many changes in porosity can be correlated to positive amplitude events and a 30 to 60 m scale of porosity variation is similar to the scale of lateral variation in amplitude.
Crosswell data integrated with porosity models can give a more accurate representation of interwell reservoir variation than that derived from normal log or core correlations or simpler stochastic modeling.