State-of-the-Art Summary

Commission, about two-thirds of the Lower Hartshorne coal volume is at a depth of 500 to 1,000 feet. Faulting is extensive and a constant factor. For the explorationists out there, Prior noted that "Lower Hartshorne coal thickness is inversely related to thickness of the underlying Hartshorne sand." Research projects are underway defining CBM potential in the Desha Basin in southeastern Arkansas.

Arkoma CBM Development: Horizontal or Vertical?

The Hartshorne coal in Oklahoma's Arkoma Basin has been brought to profitable fruition both horizontally and vertically. And fans of both will find assurance. Horizontal completions will reach a higher peak rate sooner; but their initial decline is steeper. At the four-year point, horizontal wells will produce about two and a half times as much as a vertical well. Comparative ultimate recoveries are yet to be determined, but cost data shared by speakers indicated horizontal wells will cost from between two and a half to four times higher than their vertical counterparts. The perspective from which one approaches the problem influences the answer regarding which approach is best. As one speaker sagely advised, "Do what you know well."

El Paso Production Company is a powerhouse of horizontal-well development in Oklahoma's

Arkoma Basin. Curtis Matthews, senior geologist, shared his horizontal-well success tips:

1. Exercise good well planning
2. Use an experienced directional driller
3. Employ a good wellsite geologist
4. Know the area geology (3-D visualization helps)
5. Have patience

And he should know. El Paso stays within a 4-ft-thick coal more than 90 percent of the time! This includes when laterals encounter small faults of a few feet displacement. Too small to be inferred from geological information, El Paso's experience is to expect them. When crossing a fault, one must get back in the coal quickly. But do you go up or down? Matthews advised that one should go up about 75 percent of the time. In addition, he notes that if sand is right on top of the coal, it may be time to turn in rather than endure the inevitable money pit that follows.

For vertical wells, minimalism has merit. John Wendell of Wendell Consulting shared his expertise developing Arkoma Basin vertical CBM wells. He stresses cost containment across the board. He gave one example regarding injection falloff testing to measure permeability. A vendor can do this, but the costs can add up. So Wendell built his own injection falloff-testing rig for roughly the cost of a single service job. It did not have leather seats and a sunroof, but it got him there; and it was a capital expenditure.

Artificial lift is generally required to keep water lifted off CBM wells. While conventional rod pumps are common, there are disadvantages: volume limitations; fines; maintenance costs, etc. Brian Weatherl of Source Rock Energy Partners discussed two increasingly popular alternatives. These include soap injection through capillary strings using gas-powered pumps and a simplified gas lift. Soap injection is cheaper than using rod pumps and lifts similar capacity. And it is maintenance-friendly. Using a simplified gas lift, setting a wellhead compressor and injecting gas back down the annulus, also has an economic advantage.

Great Things
to be Achieved Unconventionally

The abundance of expertise in Oklahoma City created the kind of enthusiasm that multiplies. "I certainly enjoyed the presentations I saw that dealt with the Hartshorne coal and horizontal drilling. They were done well and I enjoyed being informed on horizontal drilling in the Arkoma Basin," notes conference attendee Ed Butler, who is in charge of engineering and planning for CDX Gas LLC. Butler agrees that this technology will be important over the long haul. John Dewey of Vintage Petroleum added: "I thought the conference was very good; it was informative, the papers were well done and the turn out was very good."

"I was very impressed with the technical presentations and the technical knowledge presented," noted Robert Gibson, one of three Questar Exploration and Production attendees at the conference. He continues: "Anybody that came could take something away-either an awestruck type of perspective of how much tight gas sands, coalbed methane and shale gas has contributed to increasing overall gas supply in the United States or, at a more microscopic level, a good understanding of the maturation process for these types of reserves. We've been producing these things since the turn of the last century. It's becoming more and more a part of our domestic overall U.S. gas supply and its projected to increase even more over time."

For further information, contact Lance Cole at lcole@pttc.org.

Oklahoma CBM Annual Production