Development of continuous-type, i.e. unconventional, hydrocarbon accumulations inarguably has transformed the energy outlook of Canada and the United States.
Now, the future of European and global energy markets may be determined by the extent to which these type accumulations can be developed outside North America, according to AAPG member Don Gautier, a U.S. Geological Survey research geologist in Menlo Park, Calif.
The USGS is hard at work to nail down an estimate.
In cooperation with European geoscience organizations, the agency kicked off a program in October 2010 to assess potential additions to reserves from continuous-type gas and oil accumulations in fine-grained rocks of Europe.
The initiative is part of the World Petroleum Project funded by the United States for a number of years via an Act of Congress. The entity provides information/advice to the president, Congress, DOI and the public at large about global resource potential.
“It’s seen as in our political interest to have somebody commenting objectively and scientifically about future resources that might be available,” said Gautier, who serves as principal investigator for the World Petroleum Project.
“We have limited staff and budget,” Gautier said, “so we have to sort of choose our battles and try to prioritize and do what we think in our scientific judgment are the most urgent and important.”
Examples of the agency’s efforts include a world petroleum assessment published in 2000, which provided an estimate of the world’s undiscovered conventional oil and gas. The results of a study of the Circum-Arctic resource potential were published two years ago.
“Our point of view is that one of the most important things we should be working on now is trying to form a solid scientific opinion about the potential for additions to reserves worldwide from unconventional, or continuous-type, resources,” Gautier emphasized. “One of the most important and urgent of those is global shale gas and also the tight gas sands and coalbed methane.
“Part of that global study of unconventional resources is this assessment of shale gas,” he noted, “and, in particular, our strategy for assessment of potential additional reserves from unconventional resources in Europe.”
When compared to conventional reservoirs, continuous type accumulations in mudstones are a whole different breed of cat, in that they:
- Are laterally extensive.
- Don’t necessarily coincide with structural and stratigraphic traps.
- Lack well-defined down-dip petroleum/water contacts.
- Don’t appear to be localized by buoyancy forces.
- Typically contain both source and reservoir in the same formation.
The planned strategy for the current project entails the use of North American analogs, attempting to use results of drilling and exploration development of these types of resources in the United States and Canada.
The USGS is seeking the best local geological expertise available within the collaborating European geoscience organizations that would have the most advanced information locally. The agency is optimistic the groups will think it is in their best interests to use the methodology and analogues from North America along with their local geological expertise to help define plays to be used in the assessment.
Drawing on the geological circumstances and well performance observed in analogous North American gas shales, the USGS has developed a probabilistic, geology-based methodology to evaluate the potential for technically recoverable hydrocarbons in continuous accumulations in Europe, according to Gautier.
He noted that instead of calculating in-place resources and estimating recovery efficiencies, the current USGS methodology is performance-based.
“Candidate formations are screened for particular geological criteria, and geologically defined assessment units (AUs) are specified,” Gautier said. “Potential additions to reserves in each AU are evaluated using four input distributions:
- Play level risk.
- Volumes of potentially productive formations within the AU.
- Optimal well density.
- Estimated ultimate recovery per well.
“The four distributions are combined in a Monte Carlo simulation that yields a probability density of recoverable resources that can be further evaluated for resource/cost relationships,” Gautier said.
“The important thing is using our methodology and North American experience to make a scientifically, geologically based consistent set of estimates for potential for shale gas and other unconventional resources in Europe and elsewhere in the world,” Gautier commented.
“That’s the essence of it.”