Drilling rig image via shutterstock. Reproduced at Resilience.org with permission.
Last week, members of the media breathlessly reported—based on a new study published by West Virginia University (WVU) entitled A Geologic Play Book for Utica Shale Appalachian Basin Exploration—that the Utica Shale could hold more recoverable gas than the Marcellus, the largest shale gas play in the country. The “Play Book” provides an interesting roundup of geological data on the Utica and associated shale units. However the sensational claim that these units contain a mean resource of 782 tcf (trillion cubic feet) of “technically recoverable” gas, 1947% higher than the USGS estimate of 38.2 tcf made in 2012, has little credibility.
Of course, one can get any “technically recoverable” resource number one wants, depending on input assumptions. Critical assumptions for the gas estimate are:
- Area assigned to sweet spots and non-sweet spots.
- Drainage area of individual wells.
- Estimated Ultimate Recovery (EUR) of wells.
- Success ratio of wells.
(Units are Acres) | Minimum | Mode | Maximum | Mean |
USGS Total Area | 25,800,000 | 31,600,000 | 37,400,000 | 21,600,000 |
USGS Sweet Spot Proportion | 0.09 | 0.21 | 0.50 | 0.27 |
USGS Sweet Spot Area | 2,322,000 | 6,636,000 | 18,700,000 | 5,832,000 |
WVU Assessment | Not stated (map only) |
(Units are Acres) | Minimum | Mode | Maximum | Mean |
USGS Drainage area per well | 120 | 150 | 180 | 150 |
WVU Assessment | Not stated |
(Units are billion cubic feet) | Minimum | Mode | Maximum | Mean |
USGS assessment | 0.2 | 0.6 | 1.1 | 0.619 |
WVU assessment | 0.19 | 7.09 | 30.37 |
(Units are percent successful) | Minimum | Mode | Maximum | Mean |
USGS assessment | 75 | 85 | 95 | 85 |
WVU assessment | 90 | 95 | 99 |