Fishbones created an acid jetting technology to stimulate wells in carbonate reservoirs without conventional fracking. Now the company has adapted the technology for sandstone, as Jennifer Pallanich reports.
The Fishbones acid jetting stimulation system is an open-hole liner completion that connects the well and the reservoir by eroding the carbonate to form a series of channels, or tunnels, that are up to 40 feet long. The technology gets its name from the distinctive needles that deliver the acid.
“When we created the concept, the use of acid to erode the carbonate was the fundamental technical piece,” says Kevin Rice, Fishbones’ regional manager for North America.
Rune Freyer invented the Fishbones technology and founded the Norway-based company of the same name. He also founded Easywell, which he sold to Halliburton in 2005, to sell a swell packer technology he created.
Each Fishbones sub is attached to a 40-foot liner joint and deploys into the wellbore with four 40-foot titanium needles. The resulting 43-foot joint can be made up at the rig site. Rupture disks cover the needle nozzles before the stimulation phase, so fluid can circulate without damage to the needle nozzles.
When the subs are in the required location in the wellbore, hydraulic pressure activates the needles. The needles push through specially angled holes and use the nozzles at their tips to jet acid into the carbonate formation. “This creates a tunnel,” Rice says.
As the fluid, typically 15% hydrochloric acid, jets and dissolves the formation, the needles from all the subs simultaneously push out into the reservoir in a pumping operation that lasts four to five hours.
One Fishbones sub can create four laterals, and the company’s proprietary SimFish simulator helps determine the appropriate number of laterals to create.
Each sub also has two production valves, which allow hydrocarbons to enter the liner.
“You are creating a high number of channels simultaneously” over five to six hours, says Fishbones chief executive Eirik Renli.
Rice believes about 300 laterals, or 75 subs, is the upper limit, based on typical pumping requirements.
The Fishbones sub requires a flow rate of eight to 12 barrels per minute, delivering about 3500 psi to the needles. “The beauty of that is, that results in a much lower horsepower requirement than anything you would normally need at the surface for a more traditional treatment,” Rice says. “And it’s thousands of gallons, not millions.”
That translates to lower costs and less time for operations, Renli says. “You do need some acid, but from an environmental point of view, you are using significantly less fluids and significantly less time and significantly less infrastructure to do the job,” he says. “You can avoid traditional fracking.”
Because neither the needles nor the resulting tunnels can extend beyond 40 feet, it is possible to avoid wet and gassy zones when their locations are known. Once the needles are fully extended, the treatment concludes, and production can begin.
Renli notes the technology controls distribution of the acid and prevents laterals that extend beyond 40 feet, which helps avoid stimulating surrounding layers.
The Fishbones subs are available in 5 ½-inch tools to fit inside an 8 ½-inch open hole and 4 ½-inch to fit a six-inch to 6 ½-inch open hole. The technology is applicable to production and injection wells. Other potential uses are for steam-assisted gravity drainage.
Field tests
The Joint Chalk Research (JCR) group, comprising BP, Statoil, Eni, Total, Hess, Maersk, Dong, ConocoPhilips, and Danish North Sea Fund, financed the jetting system’s first test in carbonates. Working with the JCR group, Fishbones identified spots for field trials in low-risk and low-cost Texas land wells.
The initial Fishbones sub field test was in the Austin Chalk in April 2014. In that trial, the company deployed 15 Fishbones subs to create 60 new laterals in a 20-year-old well producing just 1.5 barrels per day.
The intent of the test was to establish mechanical integrity of the system. The operator had planned to plug and abandon the well after the test.
Fishbones model shown with needles extending during acid pumping operation.
“It was an old open-hole well that had been aggressively steered. We had to rotate 10 hours to get it to bottom,” Rice says. “Once it reached the bottom, it was still able to perform as expected. It was a harsh test on our tools to make sure they were rugged.”
“We saw a dramatic increase in the productivity of the well,” Rice says. Following the Fishbones sub jetting stimulation, the well increased to 11 barrels per day and has sustained that over 18 months.
Rice says the test proved the equipment can be employed in a downhole environment safely.
“It was good proof that the stimulation effect was real and apparent and could potentially reinvigorate old wells,” Rice says.
In July 2015, Fishbones deployed the same system in a similar set-up in the Buda formation in Texas. Again, 15 Fishbones subs created 60 new laterals over the course of a five-hour pumping operation.
“There was a significant increase in production,” Rice says, noting initial production in the first month was six times higher than before-treatment rates.
“Again, it was quite a successful test in a carbonate environment. It allowed us to feel the technology is appropriate for service,” Rice says.
Fishbones subs have also been used in Indonesia and the Middle East. In Indonesia, the jetting system was used in a coalbed methane application. The Indonesian application exceeded the operator’s expectations, Rice says. The Middle East deployment proved the Fish Basket tool, which was used to clean up the remaining titanium needles in the liner. “It was successful in retrieving 100% of the remaining needles in the liner,” Rice says.
Additional wells are being scheduled, Renli says, predominately for Middle East carbonates.
Dreamliner
Globally, about 45% of production comes from carbonates, 45% from sandstones, and 10% from shales. Fishbones’ jetting technology addressed the carbonates, but the company wanted an alternative for sandstones. It worked with Innovation Norway in a joint industry project supported by Eni, Statoil and Lundin to develop the Dreamliner sub.
“You are not able to dissolve sand with acid, and the sandstone grains are too heavy to be jetted,” Renli says.
Fishbones jetting proved effective at stimulation, Rice says. “But if it’s not carbonate and you can’t use acid to dissolve the rock, how do you make the same laterals? We finally settled on drilling as the best way to make the laterals.”
After considering several possibilities, the company decided to tweak the original system in a way that made it possible for the needles to drill instead of jetting acid.
The Dreamliner sub uses the same type of needle system, although only three needles, each topped with a small bit, are placed in each sub. “There are a lot of moving pieces, but the design is very simple and very mechanical,” Rice says.
Essentially, once the liner is installed and the Dreamliner sub is in place, liner fluid is circulated, which turns turbines inside the sub assembly to turn the bits, thereby providing the needed thrust to drill the very small laterals.
As with the Fishbones jetting system, all the needle drilling is done simultaneously, allowing three narrow laterals per sub to be drilled over the course of four or five hours.
According to Rice, if one of the needle bits stops, the others can continue drilling independently until they have come to the end of their 40-foot reach.
Pre-job planning requires a core sample on which Fishbones can do a drilling test to determine the flow rate and weight on bit needed to achieve the target drilling rate of around 10 feet per hour.
The first Dreamliner trial took place at Statoil’s Smorbukk South well off Norway in July 2015. Four-dozen Dreamliner subs were employed to help the operator stay in an oil-bearing formation while avoiding a nearby gas-bearing formation. In total, 144 laterals were created in about five hours of pumping time without requiring additional pumping equipment beyond the rig pumps.
Fishbones deployed 48 Dreamliner subs over the 2012 metre (6600 feet) open-hole interval to a total measured depth of 6546 metres (21,474 feet). Subsequent mud circulation over a period of six hours, using only rig pumps, enabled drilling of 144 needles, creating laterals extending in a radial pattern from the mother bore. The main objectives for using the Dreamliner sub were to connect the reservoir without stimulating into the higher permeable gas formation below the target sand.
According to Statoil, the hydrocarbons in the Smorbukk South Extension project are in reservoirs with varying porosity ranging from what the operator describes as “bricks to tiles”, where fracking was not feasible. Statoil said production rates to date were considered a success.
“How much more can you extract from reservoir with Dreamliner? The answer is that depends on the reservoir. Every well is different,” Renli says.
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