Drilling by Union Pacific Resources and its partners has established a new productive carbonate buildup trend, delineated by 3-D seismic, that is significantly down dip of the previously established fairway. Production was established in this trend by the UPR Bearcat #1 with an IP of 26 MMCFGPD. Analysis of wireline logs, conventional and rotary sidewall cores and sample cuttings indicates that this trend differs considerably from the coral-dominated, shallow-water reefs that were modified by meteoric waters as described in other Cotton Valley reservoirs.

Evidence suggests a low-energy, deeper-water setting for the buildups, which are primarily mud mounds with a faunal content dominated by calcareous sponges, chaetitids, Tubiphytes, tubular molluscs, worm tubes, bryozoans and echinoderms. The lime mud matrix exhibits microbial fabrics and contains an abundance of calcareous sponge spicules and calcispheres. Syndepositional megascopic shelter pores (stromatactoid-type cavities) are common, but have been largely occluded by cements. The rock data does not support physical erosion of these buildups by subaerial exposure or meteoric processes. Bioerosion and endolithic boring seem to dominate.

The buildups along this down-dip, deep-water trend are generally taller than those identified elsewhere, achieving thicknesses in excess of 900 feet (270m). The porosity within the reservoirs consists of remnant primary porosity as well as burial-related dissolutional microporosity. The porosity distribution within the buildups may be highly variable and some features may be a complex of coalesced buildups.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah