Prediction of Reservoir Geometries in the Morrow of Southeastern New Mexico

MAZZULLO, LOUIS J., Consultant, Midland, TX

The 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. In particular, environments identified within marginal marine facies tracts in the Morrow indicate that the shoreline was constantly shifting in response to relative sea level changes. Depositional processes were sensitive to varying sediment discharge rates as well as sheltering by offshore carbonate mounds. Sandstone/carbonate sequences also indicate periodic reworking or drowning of marginal marine sediments throughout the Morrowan, which was especially prevalent in middle Morrowan time.

The southern shelf of Belize, Central America, offers an excellent analog to depositional processes that were operative during the Morrowan in southeastern New Mexico. Modern facies tracts along the Belizean shoreline respond to varying discharge rates of sediment from the Maya Mountains source area to the west and to sheltering from the offshore barrier reef and other carbonate mounds. Carbonates are actively developing upon drowned beach ridges and channel mouth bars, and there is evidence of drowned fluvial channels several miles from present-day shoreline. Depositional patterns in Belize are identical in scale to those believed to be operative in the Morrow and offer analogs that are useful as predictive tools for exploration and development.

AAPG Search and Discovery Article #91008©1991 AAPG Mid-Continent Section Meeting, Kansas Geological Society, Wichita Kansas, September 22-24, 1991 (2009)