Ranking the Resource Potential of the Woodford Shale in New Mexico

Abstract The Upper Devonian Woodford Shale ranges from a thickness of 0 ft to 300 ft and is found at depths of 7,000 ft to 18,000 ft in the Delaware Basin. The Woodford is thermally mature over its entire extent in New Mexico: In the deeper parts of the Delaware Basin, it is in the thermogenic gas and condensate window; on the Northwest Shelf and where present on the Central Basin Platform, it is in the oil window (Broadhead 2010). Southeastern New Mexico is subdivided into Regions I, II and III based on the intensity of the fracture networks, thermal maturity and Total Organic Carbon (TOC) (Comer 2005). Miller's (2010) gas shales ranking scorecard used parameters like total organic carbon, vitrinite reflectance, shale thickness, gas-filled porosity, clay content, quartz content, fluid compatibility, natural fracture intensity, tectonic stress and reservoir pressure gradient. The range of the scale of ranking is 0 to 100 points and for reference, the Barnett has 73 points. The better the total points, the better are the prospects of finding shale gas. Each of the regions (Regions I, II and III) were ranked for the prospects of shale gas using Miller's (2010) ranking scorecard and assigned a score of 68, 66 and 48 respectively. The results showed that Region I and II have better chances of finding shale gas. Finally an assessment was made to quantify the volumes of oil and gas in-place using Comer's (2005) Hydrogen mass balance method. The estimated volumes were 36 billion barrels of original oil in-place and 44.5 trillion cubic feet of original gas in-place in comparison to 119 billion barrels of original oil in-place and 230 trillion cubic feet of gas in-place in the Woodford for the entire Permian Basin (Texas & New Mexico). The assessment confirms that Woodford shale is a major unconventional source of both oil & gas in New Mexico.