Abstract

Mescalero Escarpe Field was discovered in 1984 by Cities Service Oil and Gas Company. The field is located in Lea County, New Mexico, south of the Northwestern Shelf in the northernmost part of the Delaware Basin. Mescalero Escarpe Field is a pure stratigraphic trap with a reservoir in carbonate slope detritus of the Bone Spring Formation (Leonardian, lower to middle Permian). Four main lithologies are present in and around the main reservoir interval: (1) dolomitized conglomerate/breccia, (2) dolomitized bioclast-peloid packstone, (3) laminated dolomitic mudstone, and (4) very fine-grained sandstone. The conglomerate/breccia and bioclast-peloid packstone are the main reservoir lithologies with dolomitic mudstones acting as both source rock and seal. The reservoir lithologies are overlain by and pinchout updip into dolomitic mudstones. The bioclast-peloid packstones and conglomerate/breccias are concentrated at the toe of slope in channels cut into the underlying sandstone.

Cyclic deposition of slope strata as outlined below was apparently related to fluctuations in relative sea level. (1) When sea-level rise was rapid, the shelf was flooded, and some carbonate sediments were carried off the shelf, down the channelized slope and into the basin. Peloids and fossil fragments were deposited mainly at the toe of slope (forming bioclast-peloid packstones), while micrite was deposited higher on the slope and deeper in the basin (forming dolomitic mudstones). (2) As sea-level rise slowed or stopped, the vertically-building shelf ap proached sea level causing a marked decrease in production of carbonate material on the shelf. Submarine erosion of the shelf margin created clasts that were carried downslope by debris flows, and deposited at the toe of slope (forming conglomerate/breccias). Carbonate mud was deposited penecontemporaneously in areas of the slope and basin not affected by debris flows. (3) When sea level remained static or dropped at the end of depositional cycles, the shelf was at sea level or emergent. Terrigenous sand then moved across the shelf and into the basin.

Virtually all porosity in slope detritus at Mescalero Escarpe Field is diagenetic. Main pore types are molds, intercrystalline voids (between dolomite crystals), and fractures. Petrographic and stable-isotopic evidence support replacive dolomitization shortly after deposition in deep seawater undersaturated with respect to calcite. Those dolomitizing waters were also probably responsible for dissolution creating moldic and intercrystalline porosity. Petrographic evidence indicates that fracturing occurred shortly after deposition and replacive dolomitization. Anhydrite is an important late, pore-filling mineral.