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UGI: Unconventional gas wealth seen in world's basins

G. Alan Petzet
Chief Editor-Exploration

FORT WORTH, Sept. 30 -- Sedimentary basins in the US appear to contain a volume of technically recoverable unconventional gas that is 10 times the ultimately recoverable volume of conventional gas.

All resources are logarithmically distributed in nature, and the lower quality deposits need more expenditures and better technology to develop economically, Stephen A. Holditch of Texas A&M University told the opening session of Oil & Gas Journal's Unconventional Gas International Conference & Exhibition in Fort Worth Sept. 30.

Results of the studies of eight US basins are being configured into software that can be used as advisory points as operators begin to drill, complete, stimulate, and produce shale, tight sands, and coalbed gas reservoirs outside North America, where almost all of this type of drilling has occurred so far, Holditch said.

Based on the findings, which imply that vast quantities of gas can be produced in the world's basins, even Saudi Arabia's state oil company Saudi Aramco has started a tight gas sands research group, Holditch said. Holditch and a large group of his students plan to release more details of the still incomplete findings at a Society of Petroleum Engineers conference in Pittsburgh in mid-October.

C. Michael Ming, president, Research Partnership to Secure Energy for America (RPSEA), noted the importance of basic research into unconventional gas recovery technology. Partly due to such research, which is under constant threat of reduced federal and other funding, the US has more gas reserves today than when former US President Jimmy Carter made his "moral equivalent of war" (meow) speech in the midst of the late 1970s energy crisis, Ming told the conference.

World gas study
Holditch's students, who compared conventional and unconventional gas statistics from eight US basins, plan to expand the study to 25 basins.

The information covered petroleum systems descriptions and other public data on the San Juan, Green River, Powder River, Uinta-Piceance, Black Warrior, Wind River, and Illinois basins. Data came from the National Petroleum Council, US Geological Survey, Energy Information Administration, Gas Research-Gas Technology Institute, Potential Gas Committee, and other sources.

When looking at a given target basin or formation anywhere in the world, we can find the analogous basin or formation in the US and glean from published case histories that abound in the literature what amount to the best practices for recovery of unconventional gas, Holditch said.

The system, still a work in progress, is advisory in nature and not an expert system, he cautioned. Unconventional oil reservoirs have not yet been considered.

Part of the current study, for example, lists US basins and ranks world basins by most analogous, second most analogous, and so on. The software would eventually help operating companies, service companies, and others to select a tight gas sand fracturing fluid, for instance, using defaults and best practices from similar US reservoirs as a starting point, Holditch said.

Need for research
Carter delivered the "meow" speech about the same time that Houston wildcatter George Mitchell "decided to take a stab" at producing gas from the Barnett shale, Ming recalled.

Noting that the drilling, completion, and stimulation procedures for each shale must be uniquely decoded, Ming said that operators are still improving Barnett shale gas recovery factors. Some of the improvement can be laid to iterative actions, but with concentrated research, the process might become more predictive, he postulated.

The positive contributions from projects such as DeepStar, Norway's DEMO2000, and Brazil's deepwater program demonstrate that what begins as pure research can be driven toward field demonstrations and commercialization, Ming said.

RPSEA, he noted, is shepherding projects on emerging shales in Alabama, the Barnett shale, treatment and management of produced and all other waters, advanced hydraulic fracturing technology, how gas migrates to fill unconventional reservoirs, and how to increase the area of reservoir contact in horizontal wells, among other projects.


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