Patrick D. Doherty¹, Gerilyn S. Soreghan¹, John P. Castagna¹
(1) University of Oklahoma, Norman, OK

Abstract: Reservoir and seismic modeling of an exhumed algal mound complex, western Orogrande basin, New Mexico

Upper Paleozoic algal bioherms form significant reservoirs, but are difficult to exploit owing to characteristically pronounced facies and diagenetic heterogeneity. Establishing predictive relationships between petrophysical properties and stratigraphy is key to enhancing exploitation success in these systems. We logged and sampled a well-exposed, reservoir-scale algal mound complex of the western Orogrande basin (New Mexico) to construct an outcrop-based reservoir model for this and analogous systems.

An accurate sequence stratigraphic framework is key for meaningful modeling, but is difficult to establish in the subsurface. The studied mound consists of multiple high-frequency readily traceable sequences with porosity-enhancing dolomitization proximal to sequence boundaries, particularly in mound flank positions. The porosity model indicates that the mound flanks behave as a stratified reservoir, while the mound core is tight and therefore acts as a lateral seal. Permeability values in outcrop are below reservoir quality. Therefore, reasonable reservoir permeabilities have been applied to this framework model to illustrate the hypothetical fluid flow.

Seismic modeling shows that the stratigraphic architecture is below seismic resolution. However, rock physics measurements on twenty outcrop samples show a relationship between dolomite percentage and the ratio of compressional-wave to shear-wave velocities at in situ conditions. For a given dolomite percentage, seismic impedance decreases as porosity increases. Thus, surface seismic data could potentially be used to estimate gross reservoir properties.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana