--> Abstract: Resource Potential of Fine-grained Cretaceous Source Rocks, Wattenberg Gas Field, Colorado; #90063 (2007)

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Resource Potential of Fine-grained Cretaceous Source Rocks, Wattenberg Gas Field, Colorado

 

Gustason, Edmund R.1, Colleen Sherry2, Marshall Deacon3 (1) El Paso Exploration & Production, Denver, CO (2) Kerogen Resources, Calgary, AB (3) EnCana Oil & Gas, USA, Denver,

 

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, have varying percentages of insoluable material (illite and mixed-layer illite-smectite clay minerals) and calcium carbonate (CaCO3), and some 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 more than 2000 feet of core from several wells, historical production data, wire line logs from approximately 7000 wells, as well as fall-off injection tests, microseismic analysis of hydraulic fractures, and production tests in several new wells, the original 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 are difficult to fracture-stimulate. However, they probably form the top and bottom seals for the Wattenberg shale gas resource play.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California