Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Predicting higher-than-average permeability zones in tight-gas sands, Piceance basin: An integrated structural and stratigraphic analysis
The Colorado School of Mines, Golden, CO
Bill Barrett Corporation
The US Potential Gas Committee recently showed a monumental increase in US natural gas reserves, from 1,532 TCF to 2,074 TCF (Curtis et al., 2009). The 35% increase is the largest gas-reserves increase since the inauguration of the Potential Gas Committee in 1965, and is largely due to the inclusion of unconventional resources such as “tight-gas” sandstones (Mouawad, 2009). The enormous domestic resources of unconventional gas will play a critical role to secure future energy sources for America, yet there are numerous challenges that must be overcome before this resource can be fully utilized. Tight-gas sandstone reservoirs have very low permeability (less than 0.01 md), which make them difficult and expensive to produce from. Even with the use of closely spaced wells, horizontal drilling and hydraulic fracturing, production may be uneconomic unless “sweet spots” are found. Predicting the higher-than-average permeability zones and maximizing production through hydraulic fracturing are some key hurdles facing energy companies that seek these resources, yet exploration strategies for these zones are relatively simplistic. Subsurface geology affects the presence and distribution of sweet spots, and can govern the success of hydraulic fracturing. Important geologic controls on production include natural fractures, depositional characteristics of the rocks and diagenesis. However, it is not yet understood how these geologic controls affect the distribution and quality of sweet spots, and how they may also affect the success of hydraulic fracturing in some cases.
The Piceance basin has been a hot-spot for tight-gas sand production technologies for more than 30 years, and has hosted close partnerships between industry and academia. We propose an integrative, basin- to reservoir-scale structural and stratigraphic analysis that aims to: (1) create a predictive regional sequence-stratigraphic correlation, (2) produce basin-scale, integrated maps of depositional and mechanical facies distribution; (3) characterize and evaluate reservoir types present, (4) define porosity type (depositional or fracture) and distribution throughout the field as well as within recognized reservoir types, (5) highlight geographic patterns in reservoir types and (6) identify potential relationships between stratigraphy, strain and fractures within the Williams Fork Formation that affect production. Our study addresses every aspect of the geosciences associated with tight-gas sands, one of our most valuable unconventional resources. This improved, fully integrated understanding of subsurface geologic controls on tight-gas sand resources will help predict critical “sweet spots” in the Piceance basin, and help us to access them in the most efficient way, with the least environmental impact.
Principal Investigators: Drs. Aschoff, Plink-Bjorklund and Trudgill
Project Duration: 2 years