Natural gas future is changing, experts say

Speakers at the 2006 Mid-Continent Coalbed & Shale Gas Symposium said natural gas found in tight sands, coal, shale and other complicated structures have gained prominence and will continue to grow in importance.

"In 20 years, unconventional resources have grown from modest expectations to the dominant domestic natural gas supply," said Scott R. Reeves, executive vice president of Houston-based Advanced Resources International Inc. "It now represents about one-third of the U.S. gas supply."

Nine of the top 13 U.S. natural gas fields are unconventional, according to the U.S. Energy Information Agency, and the more difficult rocks could represent even more of the country's production in just a few years, Reeves said. Unconventional resources are projected to increase in production while nearly all of the natural gas fields in the lower 48 states are likely to decline in the future, according to government reports.

Natural gas traditionally has been found in sandstone or other soft, porous rock. With those formations, the biggest challenge is finding where the highest concentrations of gas are hiding. Actually recovering the commodity is less difficult.

With unconventional resources, however, the challenge is reversed. Finding the natural gas is relatively easy. The shale, coal and other hard rocks contain large amounts of the fuel. The difficulty is coaxing the gas out of the solid rocks.

Producers generally use high-pressure nitrogen or some other chemical to shatter the rock. Then they inject sand or gel to keep open the cracks that allow the natural gas to escape.

While higher energy prices and increased energy demand have helped fuel the increase in unconventional energy recovery, Reeves credited technology for the bulk of the sector's recent gains.

"Technology has been the driving force previously in non-conventional production, and it will be the driving force in the future," he said.

Technology could soon help solve one of the biggest problems with unconventional wells. Most one-year-old shale and coalbed methane wells release only a fraction of the volume they spewed during their early production.

One of the reasons wells decline so rapidly is small particles of coal known as fines clog a well, preventing natural gas from freely flowing through the rock and into the well, said Stephen Ingram, of Halliburton Energy Services.

Developed in Duncan, Halliburton's CoalStim is a sticky substance that keeps the fines away from the well bore, allowing gas to flow more freely, Ingram said.

"CoalStim displaces these fines from near the well bore area, and more importantly, it stops those fines from migrating back," Ingram said.

Besides chemical solutions, energy researchers are finding that different production techniques also can help reduce common problems. Michael Conway of StimLab/Core Labs in Duncan has found the decline rate can be reduced by keeping pressure high within the coal bed methane well.

"We try to hold back the pressure," he said. "In some cases we reduce wellhead pressure by no more than 1 pound per square inch a day."

The technique is contrary to traditional thinking that lower pressure in the well will cause gas to leave the high-pressure environment in the coal. The find is just one more example of how the industry has had to think creatively to conquer challenges.