MALON, KENNETH M., Petroleum Consultant, Houston, TX; and ROBERT R. CASAVANT, University of Arizona, Tucson, AZ

ABSTRACT: Facies Architecture of the Morrow Sandstones, Southeastern New Mexico

Gas production in Eddy County, New Mexico is primarily from two sandstone sequences in the early Pennsylvanian Morrow Formation. Two sandstones sequences constitute tile primary development and exploration play in the region.

A reservoir characterization of a region centered around the White City Penn Gas Pool demonstrated that the erratic nature of tile Morrow sandstones call be deciphered and illustrated sufficiently to evaluate reservoir drainage at allowable well spacings. A "slice mapping" technique was used to characterize facies heterogeneity within tile reservoir intervals in the region. Facies types were determined from well cuttings and well-log curve pattern analyses. Chronostratigraphic reconstructions of facies variation and sandstone distributions were completed for eight genetic sandstone intervals or parasequences- Combined with structural and engineering data, the study presented a 3-dimensional assessment of reservoir geometry and performance. Subsequent infill drilling and completion strategies took advantage of tile detailed analyses.

The lower half of tile Morrow Formation consists of two distinct, coarsening-upward sandstone intervals that represent two phases of an overall southeastward progradation of fluvial-deltaic deposits. Sandstone deposition was interleaved with short aggradational and retrogradational cycles. Delta lobe abandonment and subsequent differential compaction of deltaic deposits and/or syndepositional faulting accounted for numerous cycles of marine incursion and shale deposition. The upper portions of many sandstone parasequences contain thinner units of reworked channel mouth bars, beach and barrier-bar deposits. These in turn are capped by transgressive marine shales and thin carbonate units, dominantly oolitic.

An associated regional structural study has added another dimension to the complex depositional history of the Morrow sands. integrated Subsurface and -1,eornorphic data sets demonstrate that tile structural-stratigraphic architecture and reservoir quality of the Morrow sandstones are spatially related to deep-seated basement fault fabrics.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico