SEG: Geophysics role large in unconventionals

Alan Petzet
Chief Editor-Exploration

SAN ANTONIO, Sept. 24 -- Geophysical methods will have important applications in commercializing unconventional oil and gas resources, a panel of geoscientists told the opening session of the Society of Exploration Geophysicists annual meeting Sept. 24 in San Antonio.

Chesapeake Energy Corp., which has the industry's largest land position in US gas resource plays, plans to shoot 3,100 sq miles of 3D seismic surveys at a cost of $168 million in 2007-08, said Larry Lunardi, the company's vice-president of geophysics since June 2006.

Chesapeake's 3D seismic surveys on the sprawling 18,000-acre Dallas-Fort Worth International Airport and in surrounding urban areas has found less extensive faulting than expected, a hazard to horizontal drilling for gas in the Barnett shale, Lunardi said.

The 60,000-lb. Vibroseis trucks posed no problems for the airport's 17-in.-thick aprons and runways, and gas withdrawal is not expected to result in subsidence because the shales are so tight, Lundari said.

The company is using microseismic techniques to monitor frac jobs and is tying microseismic information into its 3D seismic surveys.

Chesapeake has acquired 600 sq miles of airborne gravity gradiometry surveys in the Arkansas Fayetteville shale gas play and has found it helpful when combined with magnetic data, Lunardi said.

He foresees a wide role for geophysical methods because many of the gas shale plays Chesapeake is pursuing have wide vertical and lateral variability over short distances.

Improved techniques
Geophysical techniques will help the industry exploit smaller offshore fields, including nonturbiditic accumulations and "light" reservoirs, said J.M. Masset, Total SA senior vice-president, exploration and reservoir. Geophysical techniques are needed to improved oil recovery from offshore fields by as much as 20 percentage points, he said.

Improvements in seismic resolution are needed to enhance reservoir quality prediction and reduce the loss of energy at depth.

Electromagnetic techniques, when combined with seismic surveys, are helping companies map and characterize tar sand and heavy oil deposits, said Sverre Strandenes, group president, data processing and technology, Petroleum Geo-Services ASA.

He said the lead time for many research projects from initial idea to widespread commercial application is 16 years. Service companies are outspending major oil companies in research, and the overall industry needs to be more aggressive, Strandenes said.

Gas hydrates
The US Geological Survey has estimated 320,000 tcf of gas in place in hydrates in the US Exclusive Economic Zone, said Ray Boswell, a geologist with the US Department of Energy's National Energy Technology Laboratory. This is estimated to be one fourth to one half of the earth's volume of total organic carbon.

Gas in hydrates have proved to be detectable when they lie beneath permafrost, when their saturation is 50% or more, and when the reservoir is 25 ft thick or more, Boswell said. Bottom simulating reflectors have not proved as important as first thought but are still key objectives in geophysical exploration for hydrates.

Seven US government agencies are probing hydrates. DOE hopes to have completed research information packages for industry on arctic onshore hydrates by 2015 and on ocean hydrates by 2025. It plans to drill into hydrate deposits on Alaminos Canyon Block 818 and other Gulf of Mexico sites in 2008, Boswell said.

Contact Alan Petzet at alanp@ogjonline.com.

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