More Meat Off the Bone: New Refrac Methods Drive Production Gains
Liner hanger components and bullhead frac combinations are boosting refract results.
Nine Energy has developed a way to cut costs in refracs by using liner hangers to attach two strings of pipe. The liner hanger allows the new pipe to be attached to the previous section without running the pipe all the way back to the surface. (Source: Nine Energy)
Refracs may currently only make up 1-2% of all completions, but some basins are beginning to find value in this procedure as the supply of Tier 1 new acreage is depleted.
That is fueling continued research into improved refrac methods, as Nine Energy and BKV, the latter of which is sometimes referred to as “The Refrac King,” continue to push the boundaries of refract technology.
The first production round of most shale wells leaves the vast majority of the hydrocarbons in the ground, so there’s plenty of opportunity for refracs.
Kevin Eichinger, senior completions manager at BKV, compared that first pass to buying a turkey leg at the Houston rodeo and barely getting started on it.
“What a shame it would be if you’ve got this big turkey leg and you take just one bite out of it and you’re done with it,” he said. Refracs let operators take extra bites.
Refracs often involve relining the wellbore to frac zones that were untouched the first time around. Nine Energy and BKV offer systems involving variations on that theme.
Liner hanger allows
Greater Frac Pressure One key method to relining a wellbore for a refrac involves using liner hangers to attach two strings of pipe. In that process, the liner hanger saves costs by allowing the attachment of the new pipe to the previous section without running the pipe all the way back to the surface.
In the vertical days, there were mechanical liner hangers that worked by directly manipulating the liner. This worked to set the hanger because the liner was basically straight up and down. But, noted Don McLean, who handles business development for Nine Energy, the dawn of the horizontal age forced a change to hydraulic hangers.
The hydraulic hanger contains a solid mandrel with a setting port, he said. A piston, made of a thinner-walled pipe sealed with an O-ring, slides over the mandrel. Surface-applied hydraulic pressure is conducted to the piston, which slides up, “causing the liner hangers’ slips to bite into the casing and attach the liner to the existing casing.” That eliminates the need to mechanically manipulate the new pipe.
The piston’s thinner wall and the O-ring have been problematic, specifically for refracs, as the frac pressure can burst the piston. In virgin production, there’s little risk of the piston bursting from overpressure because the formation’s initial pressure supports pipe and piston from the outside as the frac fluid pressures up on the inside.
In refracs, however, the formation is significantly depleted, with potentially very low reservoir pressure, meaning there is little to nothing to counteract the frac pressure. If the piston bursts, the frac fluid will rush out through and enlarge the breach, keeping the fluid from going where it needs to go. And fishing out the damaged liner hanger can be cost-prohibitive, meaning a well may have to be abandoned, McLean said.
Fortunately, that hardly ever happens, but the reason for that lies in a trade-off. Frac crews reduce the frac pressure, but that also reduces the effectiveness of the refrac. In that dilemma, Nine and its partner NewGen Systems saw an opportunity to create a new tool to meet that need.
Rescue the perishing with new tools
The new tool is their new 15,000 psi liner hanger, designed to remove any potential leak paths in the tool. It is tentatively slated for its first field trials in the Eagle Ford Shale in South Texas in May. Because it can withstand pressures of up to 15,000 psi, it will allow frac crews to use higher pressure in refracs, making the refracs more productive.
McLean is most excited about how this technology can rescue some wells from the scrap heap, mainly those with damaged parent casing.
“When our customers are identifying refrac candidates, wells that have damaged casing above where we wanted to set the liner top and they knew they were going to have to run a frac string, they kicked those out or pushed them to the bottom of the list,” he said. “That’s because customers knew that high-pressure fracs could damage the equipment, and there was no clear way to remediate the issues. By this new tool removing that risk, now those wells can be reprioritized and rescued.”
BKV’s hybrid refracs seek the best of both worlds
BKV sees early wells, with widely spaced fractures created with legacy completion designs with smaller frac volumes, as prime refrac targets. (Source: BKV)
While refracs are rare in basins with plenty of undrilled acreage, such as the Permian, they are much more important in mature fields like the Barnett Shale. That’s the view of BKV’s Eichinger.
Refracs are vital to maintaining production in the Barnett, a mature field where Novi Labs counted only one active drilling rig in mid-March. Considered the cradle of the shale revolution, the Barnett began booming with the advent of slickwater refracturing in the late 1990s, when the technology was learning to walk and talk.
Eichinger sees those early wells, with widely spaced fractures created with legacy completion designs with smaller frac volumes, as prime refrac targets. He says BKV’s new system combines the best features of bullhead and liner refracs, delivering results comparable to relining the whole wellbore at a much lower cost.
Stepping beyond pump and pray
Known to some as “pump and pray,” bullhead fracs involve pumping new frac fluid without any frac plugs that would create new fracs in previously untapped zones. Eichinger says success in the Barnett isn’t a matter of hope. It’s closer to a guarantee.
“As opposed to the single planar geometries that you’ll get in a lot of basins, the fracture complexity assists us in getting the better support from the bullheads that we do,” he said. “We get good success with those,” especially when considering estimated ultimate recovery (EUR). He added, “Bullheads do an extremely good job on shorter laterals,” especially if the originals have a small cluster count. But in longer laterals, basically anything over 2,300 ft to 3,000 ft, the per-foot EUR return diminishes greatly.
Because they involve no relining of the wellbore, bullheads are attractive primarily because their simpler operations mean lower cost and risk.
BKV “wanted to capture the benefits of both worlds,” Eichinger said, which meant limiting the portion being treated as a bullhead.
“This is like a longer stage, but with a limited treatment interval that we thought would work well for a bullhead,” he said. “And then for the rest of it, we wanted to effectively, beyond that distance, break this into the individual stages to get a higher cluster count without adversely affecting cluster efficiency.”
Because “a bullhead can do a really good job up to a certain distance,” some areas do not need a liner. The newly added clusters come further along. By using expandable liners and setting a plug below them, “you get basically a liner job in the section between clusters where you can set a plug between the end of the expandable patch and the shallowest existing cluster of the bullhead stage, but you don’t have to pay for a liner for that distance. That’s the benefit of refracturing a well with wide cluster spacing.”
The result is like lining half the well and bullheading the other half, while actually lining only 8% of the well, he noted.
Results more like a liner
In the field, Eichinger said, they expected production increases to be between those generated by a bullhead and those from a liner.
Instead, “We beat not only the bullheads’ field-wide average and median, but also the field-wide average of legacy operated liners,” he said. “It’s performing more like a liner.”
Gas chemical tracer tests proved that it wasn’t luck—they didn’t just happen to hit a natural fracture.
And because the procedure uses an expandable patch, with a large inside diameter, there’s room to “pump down wireline to break up states all the way to the next cluster. You can clean out, produce through, you’ve got less flow resistance because you’re producing through a larger diameter,” he said. The larger diameter also means less horsepower is required for the frac.
Now there’s no need to toss that turkey leg after the first bite. Refracs make it possible to get far more of the hydrocarbons out of a play.
This conversation is moderated according to Hart Energy community rules. Please read the rules before joining the discussion. If you’re experiencing any technical problems, please contact our customer care team.
