Barnett Shale Play Can Be Complex
Their Success Doesn’t Ensure Yours
Barnett Shale related stories in Explorer's October 2007 issue
Operators big and small continue to grab attention for their efforts in the high-profile Barnett Shale play in the Fort Worth Basin.
Sometimes overlooked in all the Barnett buzz, however, is the fact that myriad crucial operations are required to turn the operators’ drilling targets into actual wells and – ideally – successful producers.
It’s not easy.
This play has a lengthy track record for experimentation, success and also failure, among the 6,500-plus vertical, deviated or horizontal tests or producers drilled since the initial Mitchell Energy well in 1981, according to Randy LaFollette, manager of geoscience technology at Houston-based BJ Services.
“From the standpoint of a service company, we’re trying to sort through what the issues are, what really drives production results in the Barnett – there’s no simple, one-size-fits-all recipe for success,” LaFollette said.
“There’s a certain basic reservoir quality that’s there in terms of gas-in-place and deliverability – and these are two hugely different things,” he noted. “The hard part is to try to deconvolve the effects of reservoir quality from the effects of stimulation treatment – and from everything that happens from the time the drill bit penetrates the top of the formation to present day.
“There are many fuzzy relationships, many non-linear relationships involved,” LaFollette noted, “so it becomes much more complex than trying to sort out what works and what doesn’t on a spreadsheet.
“We’ve been in the Barnett for a long time,” he said, “and it’s an ongoing study.”
New Technologies Emerging
Barnett production patterns analyzed using GIS methods show clear evidence of sweet and not-so-sweet spots, according to LaFollette.
He also noted GIS has opened eyes in the engineering community where the engineers have been posting more stimulation treatment data on maps along with production results and reservoir quality information when available.
BJ currently is studying the combo of GIS with other data mining techniques, e.g., automated computer algorithms or neural network technology.
Slick water fracs and horizontal drilling have been key to the Barnett play’s success overall.
Going forward, a couple of other technologies that have the potential to become increasingly beneficial are simultaneous fracturing of horizontal wells (simo-fracs) and ultra-lightweight proppants.
The basic blueprint for simo-fracs entails taking two horizontal wells that are in close proximity and roughly parallel to one another and then fracing each at once.
Simo-fracs initially entailed dual fracs, one in each of the two closely spaced horizontals. Today, however, there are tri-fracs (often dubbed trifectas) and even quad-fracs being applied.
“Given such low matrix permeability of the shale reservoir, a gas molecule in the lifetime of a well may only be able to move through the matrix on the order of feet,” LaFollette said. “You need to provide very closely spaced fracs to have a very nearby, high permeability pathway for the gas molecule to migrate and move into the wellbore.”
The theory behind simo-fracs is they may increase the density of the hydraulic fracture network, or increase the amount of surface area being created from the frac job, LaFollette noted.
“You can envision it to be like a sheet of auto glass and smacking it with a hammer,” he said. “It cracks in a complex fashion, and this is probably what hydraulic fractures in the Barnett look like.”
Regarding the value of ultra-lightweight proppants in the Barnett, the jury is still out.
“When they first came out, they weren’t capable of handling some of the frac pressures in the Barnett,” LaFollette said.
“It’s not known if the ultra-lightweights are going to take off and prove beneficial in the Barnett because we’re just getting to the point with the strength of the ultra-light-weights where they can handle the Barnett closure stress range.”