Abstract

The Lower Pennsylvanian Morrow Formation of southeastern New Mexico is comprised of facies that were deposited in a complex of mixed siliciclastic and carbonate depositional environments. Reservoir geometries in gas-bearing sandstones are highly variable and identify a number of different depositional environments. These depositional environments reflect numerous glacio-eustatic events that occurred repeatedly throughout this period. As a result, even smaller-scale sequences within the Morrow are often marked by different depositional geometries. Sandstone/carbonate sequences also indicate periodic reworking or drowning of sediments throughout the period, periodic exposure and erosion at intraformational unconformities, and early post-depositional structuring within the section.

Exploration for and exploitation of these complex sandstone reservoirs need to take into account the varying styles of reservoir development that can arise from such a complex interplay between sedimentation and glacio-eustatic influences. Because sandstone reservoir morphologies can be so variable, it is important to understand the mechanism by which these reservoirs are deposited as well as the differing trends that are imposed upon multiple sands in a given sequence. An understanding of the precise depositional settings of individual Morrow sequences is the key to successfully implementing exploration and development programs that are aimed at discovering new reserves and enhancing production in existing fields.

The southern shelf of Belize, C.A. offers an excellent analog to depositional processes that were operative during the Morrow. The geology there shows a striking similarity to the Morrow in terms of its tectonic development, spatial relationships of carbonate and clastic facies systems, and scale. When viewed in the context of a basin-wide study of the Morrow, the modern example offers analogs that are useful as predictive tools for exploration and development.