Since the 1970s, various private and governmental agencies have conducted studies to
assess potential unconventional gas resources, particularly those resources contained in
tight sands, fractured shales, and coal beds. The US Geological Survey (USGS) has
assessed the amount of unconventional gas resources in North America, and its estimates
are used by other government agencies as the basis for their resource estimates. While
the USGS employs a probabilistic methodology, it is apparent from the resulting narrow
ranges that the methodology underestimates the uncertainty of these undiscovered,
untested, potential resources, which in turn limits the reliability and usefulness of the
assessments.
The objective of this research is to develop an improved methodology to assess potential
unconventional gas resources that better accounts for the uncertainty in these resources.
This study investigates the causes of the narrow ranges generated by the USGS analyticprobabilistic
methodology used to prepare the 1995 national oil and gas assessment and
the 2000 NOGA series, and presents an improved methodology to assess potential
unconventional gas resources. The new model improves upon the USGS method by
using a stochastic approach, which includes correlation between the input variables and
Monte Carlo simulation, representing a more versatile and robust methodology than the
USGS analytic-probabilistic methodology. The improved methodology is applied to the assessment of potential unconventional gas
resources in the Uinta-Piceance province of Utah and Colorado, and compared to results
of the evaluation performed by the USGS in 2002. Comparison of the results validates
the means and standard deviations produced by the USGS methodology, but shows that
the probability distributions generated are rather different and, that the USGS
distributions are not skewed to right, as expected for a natural resource. This study
indicates that the unrealistic shape and width of the resulting USGS probability
distributions are not caused by the analytic equations or lack of correlation between
input parameters, but rather the use of narrow triangular probability distributions as input
variables.
Adoption of the improved methodology, along with a careful examination and revision
of input probability distributions, will allow a more realistic assessment of the
uncertainty surrounding potential unconventional gas resources.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/5894 |
| Date | 17 September 2007 |
| Creators | Salazar Vanegas, Jesus |
| Contributors | McVay, Duane A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 770762 bytes, electronic, application/pdf, born digital |
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