Discovery of the Weber Sandstone and Development of the Raven Creek Anticline at Rangely Field, Colorado

Ryan Grimm, Leigh Owens, Carlos Collantes, Laura Murray, Marina Borovykh, Tashika Charles, Ed Bucher, and Roy Cramer

Since the initial observations of C.A. White in 1875, the Raven Creek anticline has attracted prospectors to Rangely, Colorado. Early explorers generated numerous prospects along active oil seeps in the Mancos Formation at Rangely, leading to financial backing and discovery drilling into the shallow (400-700 ft) Cretaceous shales near the crest of the structure in 1901. Continued cable-tool drilling of the Mancos targeted oil-bearing fractures, expressed at the surface as calcite-filled veins. Cumulative Mancos production exceeded 4.7 MMbbl by 1954. Exploration wells targeting the Dakota Sandstone in the 1920’s proved to be non-commercial, encountering high initial gas flows that quickly watered out, and common, sometimes spectacular, blowouts during drilling.

The Weber Sandstone discovery well, the Raven A-1, was spudded in 1931 by the California Company. The discovered giant oil accumulation of 1.8 Billion STB remained trapped within Pennsylvanian-Permian eolian & dryland-fluvial sandstones, as field development was postponed until WWII demand created a drilling boom in Rocky Mountain production. Between 1944 and 1949, 473 wells were drilled on 40 acre spacing, with as many as 63 active rigs working year-round. Part of the success at Rangely was the application of diamond core bit technology, leading to faster penetration and longer bit life in the abrasive and well-lithified Weber sandstone. This drilling method also recovered over 109,000 ft of core from over 330 wells, providing a valuable archive for continued reservoir management. Production increased with pipeline capacity, to a maximum production rate of 82,000 BOPD in 1956. Following unitization in 1957, a variety of waterflood projects were implemented and expanded with 20 acre infill drilling in 1963. The additional wells and five-spot injection patterns successfully increased production by 14,000 BOPD in 1969.

Tertiary recovery via CO2-WAG flooding began in 1986 and has significantly extended incremental production rates into the 21st century. The Weber Sandstone has produced over 840 MMbbl and continues to provide commercial production. The acquisition of 3D seismic in the field combined with modern logging and completion technologies offers multiple viable opportunities for future development.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62^nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013