Shale gas plays in the United States may have become almost commonplace, but they continue to hold on to a respectable amount of their initial wow status.
They’re still the place to be.
This is evidenced in large part by the majors and the overseas-based E&P companies who have scrambled to cut deals with domestic shale players to get in on the action, or even purchase them outright – think ExxonMobil’s announced intent to snap up XTO Energy.
One of the truly Big Daddies of the shale plays is the Middle Devonian Marcellus shale, which trends northeastward from West Virginia into New York with a potentially prospective area of approximately 44,000 square miles, according to AAPG member Bill Zagorski, vice president of geology for the Marcellus shale division at Range Resources.
As of October 2009, more than 3,500 Marcellus wells have been permitted or drilled in the Appalachian Basin since the initial Marcellus discovery occurred in Washington County, Pa., in 2004.
Zagorski noted reserve potential in this geographically extensive play is enormous. Modern estimates range from 50 Tcf to over 500 Tcf, defining the Marcellus as a major world-class hydrocarbon accumulation.
“Reported initial production rates for vertical wells range from 0.100 MMcf/d to over 6 MMcf/d,” he said, “and from 0.300 MMcf/d to more than 24.500 MMcf/d for horizontal completions.
“Key geologic and technical factors defining the Marcellus play are similar to other shale gas plays,” Zagorski noted. “They include thermal maturity, reservoir pressure, pay thickness, porosity, permeability, gas-in-place, natural fracturing, mineralogy, depth, structural style, target landing issues and fracturing capability.”
Surprising Success Story
The Marcellus initially was a teaser, with no hint of becoming a major play.
Just as with other shales, operators were accustomed to getting gas shows while drilling through the dense Marcellus rock on the way to deeper targets. But the shows weren’t considered to be a big deal.
When Range drilled the Renz #1 well in 2003 in Washington County to test deeper horizons, these targets didn’t pan out. The well did have significant gas shows in the Marcellus, which in this case proved to be the harbinger of a major breakthrough in the shale production.
Chalk it up in part to serendipity.
“I went to Houston in 2004 and tagged up with a friend trying to sell an interest in a Floyd Shale prospect in Alabama,” Zagorski said, “and the selling point was the Barnett Shale.
“That’s when a light bulb went off,” he exclaimed. “We had just drilled through the Marcellus and had a big show, and I came back with a recommendation to do a Barnett treatment on the Renz well.
“We put in a large frac in October 2004, and right after that we got some encouraging volumes in rates of gas,” Zagorski said. “It was the first large scale water frac and first decent commercial discovery in the Marcellus – kind of like the play starter for the Marcellus play.”
The key technologies being used in the play are:
- Horizontal drilling, with length of laterals being very important.
- Hydraulic fracturing.
- Three-D seismic.
Zagorski commented that while 3-D is important, the Marcellus doesn’t have as big a geohazard component as in other places. For example, issues in the Barnett such as bottom water are absent.