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Manning Canyon Shale in the Northern San Rafael Swell: A Potential Natural Gas Resource Play?

Steven Schamel and Jeffrey Quick
GeoX Consulting Inc

Across broad areas of northern and west-central Utah the Upper Mississippian is represented by two interbedded formations, the Manning Canyon Shale and the Great Blue Limestone. The Manning Canyon Shale contains minor carbonates and locally abundant organic matter, whereas the carbonate-rich Great Blue Limestone generally lacks appreciable organic matter and silisiclastic constituents. The Manning Canyon Shale is a regionally significant, potential hydrocarbon source rock. Wells completed in Manning Canyon Shale at the north end of the San Rafael Swell near Price, Utah, have shown enticing, albeit sub-commercial, natural gas flow rates. This study describes core from a vertical well in this area (Carbon Canal 5-12), which was completed in Manning Canyon Shale during early 2008 by Shell E&P Inc. Shortly after completion, testing of this well showed production rates of 78 Mcf/d and 667 Bw/d over a 63 hour period. The produced gas contained 93% methane, 4% ethane, 1.4 % nitrogen, and just 0.5% carbon dioxide, with a heating value of 1,052 BTU/scf. Down-hole fiber-optics indicated that most of the flow was from between 9124 ft to 9350 ft, roughly corresponding to the lower half of the cored interval. The 546 ft core (8805-9351 ft depths) includes the upper two-thirds of the Manning Canyon Shale and 101 ft of the overlying Oquirrh/Round Valley Formation. Nearly 90% of the Manning Canyon part of the core consists of carbonaceous shale and limestone, which is typically silty with laminar features. The remainder is largely non-carbonaceous, nodular and micritic limestone. The inorganic constituents includes sub-equal parts of quartz as silt grains and minor siliceous sponge spicules, carbonate as lime mud, microbioclasts and skeletal debris, and clay. Total organic carbon (TOC) ranges from <1% to >60% and is present as microscopic grains, macroscopic plant parts, and four thin coal beds. Despite abundant TOC, the generation potential (S1+S2) is poor to fair (0.1-6 mg HC/g rock), consistent with the high maturity (dry gas stage) and abundant inertinite (fossil charcoal) indicated by petrographic analyses. Nonetheless, inflated sealed core sample bags suggest that the Manning Canyon Shale retains some quantity of adsorbed natural gas and may have shale-gas reservoir characteristics.

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