--> Growth Phases, Internal Surfaces and Reservoir Compartmentalization in Waulsortian Buildups: Muleshoe Mound, Lower Carboniferous, New Mexico, by D. Hunt, K. C. Kirkby, J. A. T. Simo, and T. C. V. Van Den Bergh; #90986 (1994).

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Abstract: Growth Phases, Internal Surfaces and Reservoir Compartmentalization in Waulsortian Buildups: Muleshoe Mound, Lower Carboniferous, New Mexico

Dave Hunt, Kent C. Kirkby, J. A. Toni Simo, T. C. V. Van Den Bergh

Muleshoe Mound initially appears to have a simple haystack shape, but study of its stratal geometry, facies patterns, and diagenesis reveals five distinct growth phases. Each phase is bounded by surfaces, marked by scour, conglomerates and breccias, which are interpreted to reflect significant submarine depositional hiatuses. These phases and surfaces have had a profound impact on the development, distribution, and partitioning of reservoirs within the buildup. Similar patterns of reservoir variation between mound phases occur in oil-filled Waulsortian mounds in the Pekisko Formation of west-central Alberta, and a complex internal heterogeneity appears to be the norm for many Waulsortian buildups.

As a gross simplification, reservoirs in limestone Waulsortian mounds are dominated by two end members: interparticle porosity in grainy flank facies and fracture-related porosity in the cement-rich core facies. In Muleshoe each phase varies markedly in the abundance and distribution of grainy flanks facies and has subtle differences in cementation and diagenesis. The density of early fractures (neptunian dikes) in the cement-rich mound cores also appears to vary between mound phases based on the geometry of the core facies and nature of their substrate. These dike patterns may foreshadow later burial fracture patterns.

The phases and surfaces are the result of regional and temporal variations in productivity and energy, which may be related to relative sea level changes. However, Waulsortian mounds were affected by a spectrum of interrelated factors, and some pattern of interrupted growth should probably be considered intrinsic to carbonate buildups, and an important parameter in reservoir prediction.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994