AGA SEES COAL SEAM GAS SUPPLIES GROWING

Dec. 10, 1990
Coalbed methane has become a significant component of the U.S. gas supply mix says American Gas Association. Since 1983, production and well completions in coal seam areas have increased rapidly, AGA noted. "By yearend 1990, more than 1,000 wells will be producing methane from coal seams, annual production will likely exceed 100 bcf, and proven reserves will total 2 tcf or more. "in addition, recent data suggests that growth in well completions and annual production will continue at accelerated

Coalbed methane has become a significant component of the U.S. gas supply mix says American Gas Association.

Since 1983, production and well completions in coal seam areas have increased rapidly, AGA noted.

"By yearend 1990, more than 1,000 wells will be producing methane from coal seams, annual production will likely exceed 100 bcf, and proven reserves will total 2 tcf or more.

"in addition, recent data suggests that growth in well completions and annual production will continue at accelerated rates as long as favorable economic and market conditions prevail."

Exploration and production of coalbed methane is encouraged by the federal nonconventional fuel tax credit, which allows an 80/MMBTU credit until Jan. 1, 1993.

The Potential Gas Committee estimates 90.1 tcf of coalbed methane resources is technically and economically recoverable from 13 basins.

AGA pointed out that represents 11.3% of the total undiscovered gas resource base in the U.S.

Although most production and exploration has been in the San Juan basin of northwestern New Mexico and southern Colorado and in Alabama's Black Warrior basin, other basins are being studied for coalbed gas potential, AGA noted.

AGA said coalbed methane production has grown from 12 wells each producing an average 21 MMcfd in 1978 to 550 each producing an average 45 MMcfd in 1987. In 1988, the total jumped to 732 wells each producing 55 MMcfd.

TECHNOLOGICAL ADVANCES

AGA said the development of the coalbed methane industry has been aided by advances in horizontal drilling, completion techniques, completion hardware, and geologic interpretations.

Horizontal drilling has great potential for coalbed methane because coal seams are normally thin (less than 10 ft), although they may have considerable areal extent, AGA said.

"Horizontal drilling permits the well bore to encounter additional footage of coal. Not only is more coal exposed to drainage, but perforations and fracturing fluids can be strategically located in the horizontal sections, thus connecting natural fractures (cleats) with induced fractures."

In completion techniques, AGA said research has indicated the most effective induced fracture pattern for coals is that of a relatively large single planar vertical fracture, which provides the best conduit to the well bore.

"To achieve such a result, pumping pressures, fluid viscosity, and proppant load must be specifically engineered.

"For many coal treatments this requires high injection rates to place proppant out in the formation, considering rapid loss of the fluid medium to the cleat system in the coal."

PROBLEMS

AGA said the use of metal casing in a well bore sometimes presents a hazard to coal mining equipment.

"To reduce this hazard, length of fiberglass casing are being substituted for standard casing through the coals in some completed wells."

It said often cores must be cut to aid critical geological interpretations.

"In the San Juan basin, key cores have revealed a relationship between volcanic ash content of the cored rocks and the amount of gas in place in the coal seams. "Ash content can be measured from wireline logging tools ... eliminating the need to core the wells individually.

"Additional Western coal basins are being cored and tested to determine if the ash content/gas per ton of coal relationship established in the San Juan basin can be used in other basins."

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