The massively stacked, lenticular sands of the Piceance, Green River, and Uinta basins have been judged, by the USGS, to be the largest undeveloped gas resource in the U.S. Past attempts to produce natural gas from these formations have been, in the main, disappointing. Six advances in technology offer potential for unlocking a portion of these gas resources and turning them into near-term, low cost gas reserves:
Natural fracture detection to find "sweet spots",
Advanced well log analysis to target productive pay,
Advanced well completion and stimulation to connect pay to the wellbore,
Intensive infill development for efficient drainage,
Recompletion of old wells to add reserves, and
Best practices to reduce costs.
Field case studies at Rulison Field, Piceance Basin show how each of these technologies have been applied. The package of technologies presented in this paper may help producers develop stacked, lenticular sands in other basins.
This assessment is part of a Gas Research Institute (GRI) research project examining technology improvements for lowering the costs of future gas supplies.
Improved well siting and completion practices have revived a previously discovered, but commercially condemned tight gas play in the southern Piceance Basin of Colorado. Here, the target is the massively stacked, lenticular sands (and coals) of the Mesaverde Group, Williams Fork Formation stretching upward for several thousand feet from the top of the Rollins, through the Cameo coal and sand interval, to the gas and water transition zone below the Wasatch Formation. The bulk of the activity has been at the Rulison and Grand Valley/Parachute fields, where Barrett Resources is drilling, infilling and recompleting wells, and at Mamm Creek where Snyder Oil is active. Chevron, Occidental, and the DOE/NOSR are other participants in this gas play.
The Williams Fork lenticular sands gas play was discovered in 1959 by the Juhan #1 Fee well. The well had strong early gas flow rates giving rise to high expectations. When subsequent wells showed poor reserves (0.2 to 0.5 Bcf per well), this gas play was relegated to a low productivity, high cost natural gas resource. Still, these lenticular tight sands were judged to hold massive gas resources in-place of 100 to 300 Tcf, as estimated by the National Petroleum Council and the USGS. Four events have combined to revive this gas play and make it economically competitive, even during the past several years of low gas prices:
Improved well siting and well completion practices have significantly improved the productivity of this gas play.