Tight Gas in the Canyon Sandstones of Texas's Val Verde Basin: A USGS Assessment, 2016

The Val Verde Basin, Texas; the assessment unit (AU) boundaries approximate facies maps of the Canyon sandstones. USGS; base map, National Park Service. The key appears to swap the two Sonora units: the text places the fairway inside the peripheral unit, and table 1 gives the peripheral unit the larger area.

Using a geology-based method, the U.S. Geological Survey assessed mean resources of 5 trillion cubic feet of gas and 187 million barrels of natural gas liquids, technically recoverable, in tight-gas assessment units in the Canyon sandstones of the Val Verde Basin in southwest Texas.

The Canyon sandstones

The Val Verde Basin is the foredeep in front of the late Paleozoic, north-verging Ouachita-Marathon fold and thrust belt. "Canyon sandstones" is a collective name for several sandstone intervals laid down in deep water as that foredeep developed, in the Late Pennsylvanian (possibly Missourian to Virgilian) and Early Permian (Wolfcampian). They are the lower Canyon, Sonora and Ozona sandstones; the lower Canyon was not assessed.

The sandstones record several phases of deposition in advancing slope channels and submarine fans on the basin floor, fed from different directions: the Ozona sandstones from the southwest, the Sonora sandstones from the northeast. Maps of sandstone thickness and production data guided how the assessment units were drawn.

Four assessment units

All four lie within the Permian Basin Paleozoic Composite Total Petroleum System. About 15,000 wells have been drilled and tested in the Canyon sandstone, and over time production "fairways" have emerged where thicker sandstone brought denser drilling and production. Those fairways set the units:

• Ozona Sandstone Fairway Tight Gas AU, and the Ozona Sandstone Peripheral AU around it;
• Sonora Sandstone Fairway Tight Gas AU, and the Sonora Sandstone Peripheral AU around it.

The peripheral units' outlines generally follow the Ozona and Sonora sandstone boundaries mapped in 1995 by Hamlin and others.

Inputs

Each unit's probability is 1.0. Values are minimum / mode / maximum (calculated mean).

The original gives the Sonora Fairway success ratio a calculated mean of 95, which cannot come from a range of 85 to 95 with a mode of 90; it is left out.

Results

The results are fully risked. F95 is the amount with a 95 percent chance of being at least that large; F50 and F5 are defined the same way. The fractiles add up only on the assumption of perfect positive correlation. All liquids in gas accumulations are counted as natural gas liquids.

Gas, in billion cubic feet (BCFG):

Natural gas liquids, in million barrels (MMBNGL):

More than half the gas, 56 percent, is in the Sonora Sandstone Fairway unit.

Sources

• Christopher J. Schenk, Marilyn E. Tennyson, Timothy R. Klett, Tracey J. Mercier, Michael E. Brownfield, Stephanie B. Gaswirth, Sarah J. Hawkins, Heidi M. Leathers-Miller, Kristen R. Marra, Thomas M. Finn and Janet K. Pitman, Assessment of Tight-Gas Resources in Canyon Sandstones of the Val Verde Basin, Texas, 2016, USGS Fact Sheet 2016–3039, July 2016. https://doi.org/10.3133/fs20163039
• The map and both tables are taken from the fact sheet's PDF.