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Geologic Controls on Gas and Water Production on the Southern Pinedale Anticline

Young, Terry J., Victor Vega, Dennis Cox
BP America Production Company, Houston, TX

The southeastern terminus of the Pinedale Anticline, Sublette County, Wyoming, produces natural gas and condensate from over-pressured, naturally fractured tight sandstones of the upper Cretaceous-age Lance, Mesaverde, and Ericson Formations. The southern end of the anticline is syncline separated from Jonah Field and the gross producing interval is unusually thick (6000ft) with production ranging from 8,000 to 14,000 feet. The anticline is a relatively young structure set up on the hanging wall of the southwestward-directed Pinedale thrust fault (Law, 1989). The thrust appears to be associated with the uplifting of the Wind River Mountains and folding affects near surface rocks of early Eocene age. Hydrocarbon entrapment is structurally influenced and most productive wells are along the crest of the anticline. Reservoirs are fluvial channel fill sandstones and perhaps minor amounts of flood basin splays. Sandstones are moderate to well sorted, fine- to medium-grained litharenites and exist as isolated and lenticular sandstone bodies, multistory channels, and perhaps laterally coalesced channel belt sandstones (Hanson 2001). Pervasive and intense open natural fractures have been identified on the anticline and appear to have a significant impact on both gas and water production. In a few wells, single completion stages appear to be draining several 100 acres. Gas production is highly variable with gas rates in some 40 acre offset wells differing by a factor of 10. Water production averages between 10 – 20 bbl/mmcf with early rates commonly over 100 bbls/mmcf. Two major pressure compartments exist within the Lance formation, one at the top of the Lance and one below a middle Lance mudstone facies. Both pressure cells play a significant role in production on the southern Pinedale Anticline.