Barnett ‘Hits’ Don’t Rule Out Misses
Still a ‘Statistical Play’
Barnett Shale related stories in Explorer's September 2007 issue
Low risk, high reward.
How better to describe the Barnett shale gas play in the Fort Worth Basin?
“The risk is low because there’s little doubt that gas exists in enormous volumes in the Barnett Shale source rock,” said Thomas Bowman, exploration manager at Aspect Abundant Shale LP. “It’s estimated as much as 150 BCF per square mile at depths between 7,000 and 8,500 feet.
“The reward is great because fracture stimulation technologies and, recently, horizontal drilling have already yielded more than 2.6 TCF of gas and 8.46 million barrels of hydrocarbon liquids from the Barnett Shale,” Bowman added.
That’s the good news.
The bad news is there’s been a goodly number of failed wells in this play.
“This is a statistical play,” Bowman remarked. “We gave up conventional prospect risk to take on a different type of risk, that being more so the drilling and completion practices risk.
“If you do everything right – well placement, lateral length, keep drilling costs down, get casing centralized and even get a good completion – you still may not have a good well.”
Variables to Consider
The list of variables that must be addressed when working the Barnett is lengthy and includes:
- Well placement.
- Where to land the lateral – and how long to make it.
- How to complete.
- How many stages of frac, how large and what type of frac.
Clearly, before tackling this complex rock, you must do some serious homework – which is helped along with a bit more cooperation among the operators than is customary in the oil patch.
“There are so many people doing so many different things,” Bowman said, “and we have the ability to analyze everyone’s work. The industry has been willing to share information, and in addition to so much information sharing, there’s so much information made available publicly (through the Texas Railroad Commission).”
Aspect believes strongly in the approach of analyzing as much data as possible. It’s noteworthy they do not use their own wells for analysis, with the belief that a company must have drilled and operated at least 20 wells – Bowman noted the company is almost there – for the operators to be considered experienced.
In other words, success in the play takes time, and the learning curve is steep.
Via its analysis of lateral lengths drilled, Aspect has determined that wells in the play reach optimum recovery at or near 3,500 feet.
“We break it down to Mcf per foot of lateral length,” Bowman said. “When you go beyond 3,500 feet, that incremental addition of the foot and the Mcf per foot decreases because of several factors.
“Drilling a 3,500-plus lateral length becomes more difficult than just drilling,” he said. “You’re in the hole for more days, and the longer the open part of the Barnett is exposed to drilling fluids, the higher the risk of not getting the lateral out to projected TD.
“When you decide to keep the hole clean and flush solids out, you have to set casing through that,” Bowman continued “You’ve now had a hole exposed to the elements, which becomes difficult in that you won’t get pipe to the bottom.
“Now you have spent drilling dollars beyond some distance you’ll never get a chance to complete.”
Another chunk comes out of the budget if, say, there’s a 4,500-foot lateral requiring an eight-stage frac job versus a six-stage implementation. Another downside here is the well may not be able to flow the water back soon enough, decreasing reserves.
In the basin overall, longer laterals are accompanied by decreased success rates and a decrease in EUR, according to Bowman.
He noted Aspect considers a median horizontal length in the play to be about 2,700 feet with a median EUR about 1.7 Bcf.
Word to the Wise
If you’re new to the Barnett action or considering an entry point, Bowman has some cautionary words.
“Every time we think we know something concrete about this play, it changes,” he said. “When you take the play to other areas such as the West Texas Barnett, it’s a good starting point, but each of these areas has nuances that significantly impact economics.
“We’ve been pushing the play south toward Waco where we’ve drilled a well in the southern part of Hill County, and the rock is completely different,” Bowman said. “It’s not the Fort Worth Barnett.”