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Shale Gas Potential of the DJ Basin, Wattenberg Gas Field, Denver Basin, Colorado

Deacon, Marshall1, Robert E. Locklair2, David Hill1, Emily Miller3, Edmund R. "Gus" Gustason4

1EnCana Oil & Gas, USA, Denver, CO
2Northwestern University, Evanston, IL
3 EnCana Oil & Gas, USA, Denver, CO
4El Paso Exploration and Production Company, Denver, CO

     The Wattenberg Gas Field, in northeastern Colorado, has produced more than 2 TCFE from the Lower Cretaceous (Albian) J Sandstone and Upper Cretaceous (Turonian) Codell Sandstone. Approximately 700 feet of organic-rich, fine-grained, Cretaceous source rocks or “shales” occur stratigraphically below, within and above these main reservoirs. In ascending order, these shales include the Skull Creek Shale, Mowry Shale, Graneros Shale, Greenhorn Formation, Niobrara Formation, and Sharon Springs Member of the Pierre Shale. The shales are marine (Type II kerogen), have relatively high total organic carbon content (2-10% TOC), are thermally mature (> 0.8 Ro), are saturated with gas, and most have anomalously high pressure gradients. Approximately 60% of the wells in Wattenberg Field are faulted, but open fractures are rare.
     Based on an integration of 2000 feet of core from several wells, historical production data and wire line logs from 7000 wells, as well as fall-off injection tests, microseismic analysis of hydraulic fractures, and production tests in several new wells, 700 feet of potential “gas shales” were reduced to two intervals, the Niobrara and Greenhorn formations. Although open fractures are rare, these rocks have high calcium carbonate content and are “fracable”. Unfortunately, the two most organic-rich and gas-saturated shales, the Sharon Springs member and the Graneros Shale, have a high clay content and could not be fracture stimulated. However, they probably form the top and bottom seals for this resource play.

 

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah