Mowry Shale, Properties and Potential, Big Horn and Powder River Basins, Wyoming

Robert Sterling
Cirque Resources

The Cretaceous Mowry Shale is a prolific source rock for quite a few of the Cretaceous reservoirs in many Rocky Mountain basins, including the Big Horn Basin. A few wells have been completed out of the Mowry Shale as a bailout zone because of the shows seen while drilling through it. In the Powder River Basin there was more production encountered in vertical wells, but once again mainly as a bailout after conventional reservoirs proved nonproductive. The Mowry Shale has been the subject of several concerted exploration programs over the last couple of years in the Powder River and Big Horn Basins. Recent horizontal drilling has had mixed results A better undersanding of what makes the reservoir and the best technological solutions are necessary to advance this play to commerciality . The Mowry is a siliceous shale that ranges in gross thickness across the basins from 120 to over 400 feet. Amorphous silica content ranges from 45% to as high as 70%. There are areas in the basin where very fine grained turbidites are interbedded with siliceous shales in the Mowry. TOC content ranges from 1.1% to as high as 4.0%, but there is a relationship between lower TOC values and higher thermal maturity. There are both type II and type III kerogens present in the Mowry. The USGS has evaluated the Mowry Shale as a possible basin centered, or continuous, oil accumulation in both the Big Horn and Powder River basins. Overall reservoir characterization for the basin centered Mowry Shale is slightly different than the areas that have historically produced from the Mowry Shale in the Rocky Mountain region. Within the hydrocarbon generation window, expulsion microfractures contribute to the overall matrix of reservoir pore space, along with interparticle porosity and 'large crack' fracture porosity. Horizontal drilling with effective completion technology will be key to making this play commercially successful

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