Perforate, wash and cement technologies are offering operators an alternative to milling. Elaine Maslin reports.
When OE headlined an article about plugging and abandonment (P&A) “Pain in the annulus” back in 2016, it was with just cause.
Amounting to an estimated 48% of decommissioning costs (according to the UK’s Oil and Gas Authority) and with “train wreck” wells costing nearly double-digit million dollar figures, it’s an activity that brings in no revenues, just headaches.
There are firms looking to ease the pain, developing the likes of thermite plug solutions and plasma drilling technology. Something less exotic is starting to make in-roads into the P&A space, however: perforate, wash and cement (PWC) tools and methodologies. Norway’s Hydrawell was a first mover in the PWC space. The firm’s PWC solutions comprise a suite of tools helping to cut well P&A cost, where section milling would have been required, from ca.10-14 days to just two, when run as a one-trip solution.
The firm is assessing options for a rigless version of its latest tool portfolio, to further reduce costs, as well as technologies for barrier verification, without having to redrill the just installed barriers – for re-logging.
Who needs section milling?
|The HydraHemera system, washing (left) and cementing (right). Image from Hydrawell.|
Morten Myhre, chief technology officer, says the firm, set up initially in 2008, with a restructure in 2010, responded to industry calls, notably from ConocoPhillips in Norway, to do section milling differently, or not at all.
Section milling is normally needed when there’s not a verifiable barrier (cement) behind the casing and between the formation (either cement or creeping shale – OE: July 2017). This allows a new barrier to be set. According to regulations that barrier must be 50m across two sections, in Norway; or 30m across two sections, in the UK.
Casing milling can mean up to 4-tonne of steel has to be removed from the well for a normal 9-5/8in casing size, says Myhre, who was at Baker Hughes for 18 years before co-founding Hydrawell.
“We have found a technology that has the potential to save a lot of money,” he says.
In 2009, the firm developed Hydrawash, for wells with a single annulus. The first launch was in 2010, initially as a two-trip system. The system was rapidly transformed into a single trip system, and comprised a tubing-conveyed perforating (TCP) gun with disconnect, the HydraWash jetting tool, a cement stinger and Hydrawell’s Archimedes cementing tool, which helps circulate the cement into the annulus.
After perforations are created, the TCP assembly is dropped and left in the well. A ball drop then initiates the washing process using the HydraWash tool, with rubber cups to direct the flow. A second ball drop disconnects the wash tool, which is left below the perforations to act as a base for the cement, then cement is pumped through the stinger and is rotated through the perforations using the Archimedes tool.
Eliminating section milling – and underreaming operations – means reducing the amount of material having to be removed from the well and preventing BOP (blowout preventer) damage from swarf, etc.
Time is also significantly reduced for a section milling operation on a 50m section from ~10.5 days to three days, Myhre says.
In 2012, the HydraHemera system was introduced for wells with more than one annulus. With a high-pressure (HP) jetting system, it reduces operational risk and operation time and has now become the default tool for multiple and single casing applications.
A new version of HydraHemera has a TCP gun with auto-disconnect, the new HydraHemera HP jetting tool, an internal cement foundation tool with disconnect, a Hydra spray cementing valve, as well as the Archimedes cement assurance tool.
As with HydraWash, the TCP gun is dropped and left in the well. The internal cement foundation tool is disconnected to form a base, and then a ball drop initiates the washing and circulation with the HydraHemera jetting tool. It has normally 30 ea. 1/8in nozzles on a 2.5ft sub at irregular angles to create high-energy jets of mud – at ~450ft/sec – rotating the tool and washing up and down the perforated section to clean between the casing and the rock.
“It creates a chaotic turbulence of flow, ripping off small solids, and efficiently cleaning the annulus to be cemented,” Myhre says. Spacer fluid is then injected and another ball drop diverts flow to the Hydra cementing valve, with four 1/8in nozzles along a 3ft-long sub. This pushes the cement out at (to prevent cement de-hydration in the nozzles), through the perforations, with the aid of the Archimedes tool rotating at up to ±100rpm, and creating pressure below. This all takes about two days, says Myhre. Further, the operation is being optimized by means of CFD modeling and fluid comparison to enable installation of two plugs in 48 hours.
The first dual string job was performed in 2013. Now, 215 single and dual plugs have been installed in total by the firm, 130 with HydraHemera technology.
The tool can also be used for other applications, like well remediation, where excessive annulus pressure is present preventing wells to be producing, or for slot recovery (where the PWC technology is used to secure P&A of existing well bore, prior to side tracking the well).
The firm has been building its track record. At AkerBP’s Valhall field on the Norwegian Continental Shelf (NCS) the use of HydraWell’s PWC technology assisted in reducing P&A operations from 118 days at the first well to 20 days at the last well in a 12 well campaign.
In a 2016 presentation to the Norsk olje & gas Plug & Abandonment Forum about the campaign, AkerBP says the average days per well on the campaign were reduced by 45% and costs reduced by an average 35%, or US$210 million in total, with PWC helping achieve those results.
At the same event, ConocoPhillips Norway said that 23 wells on the Ekofisk Alpha field and 15 wells on other platforms in the Greater Ekofisk area were P&A’d with significant time savings, thanks partly to using PWC technology. The Ekofisk Alpha wells alone improved more the 70% in operation days from start to end of project.
Hydrawell continues to work on CFD modeling to investigate where the process could be further optimized. “We’re analyzing the how efficient we can clean the annulus, by optimizing perforation pattern (perf size, shots per foot, phasing, etc.), and fluid properties vs optimum wash rates. The goal is to have two, 50m plugs installed within 48 hours,” says Myhre.
Rigless work is the next challenge, however. An abandonment job with a drilling rig can take 40-45 days or more, or down to 20-22 days using Hydrawell’s PWC technology, says Myhre.
The plan is to do the P&A rigless with the 4, 5 and 7in production tubing still installed inside the (normal) 9-5/8in production casing. This means that the PWC technology operation days will most likely be less the 7-8 workdays per well (i.e. rigless days).
“The plan is to perforate the production tubing and production casing in a dual casing scenario. This is doable, but,” says Myhre, “the ‘thorn in the side’ is the verification of the installed barrier.”
Hydrawell is looking at barrier verification first, to find a way to verify the cement barrier, as logging dual annuli casing is impossible with existing logging technology without having to drill out the plugged area for re-logging purposes. Hydrawell is discussing possible solutions with potential partners, which could involve installing pressure and temperature sensors and transducers downhole, which would send data to where it could be collected.
Creating a barricade
|Archer’s Stronghold Barricade system eliminates the need for cutting, pulling and section milling. Photo from Archer.|
Archer has developed the Stronghold Barricade perforating, washing and cementing (PWC) system. It was first used offshore in the North Sea for a major operator in 2009. Since then, 110 jobs have been carried out using the Stronghold Barricade worldwide.
The Barricade washes and cleans the annulus of a perforated casing or liner in a selected formation zone or between casings, then accurately places a permanent barrier. With the addition of the one-trip TCP tubing conveyed perforation (TCP) module, the Barricade system becomes a single-trip perforate, wash and cement solution that gives a solid cement barrier.
Archers says the system can perform up to 2.5 times faster than a typical section milling operation (at ca. 2ft/hr). To give an example, section milling 50m (165 ft) of a 9-5/8in casing inside a 13-3/8in and setting a plug can take up to 148 hours or 6.2 days. Using the Stronghold Barricade system at 50m (168ft) of a 9-58in inside a 13-3/8in concentric casing annulus, and then setting a plug, takes just 60.5 hours, or 2.5 days, says Thore Andre Stokkeland, Archer Oiltools’ Product Line Manager for P&A Solutions.
In a PWC job performed for a major operator in the UK, Archer created a rock to rock barrier and isolated pressure from the overburden. The PWC to achieve a 550ft cement plug with a 168ft solid lateral barrier was completed in five hours. The total time from run in hole (RIH) until the tool was at surface was 15.5 hours from a depth of 2431ft. The plug was verified by load and pressure test. A rock-to-rock barrier was achieved in 15.5 hours, which exceeded the customer’s expectations and sets a new benchmark in PWC efficiency, Stokkeland says.
“The above-mentioned time and cost savings are a result of eliminating the need for section milling. Milling casing would be challenging due to limited swarf handling capabilities and surface equipment to handle metal swarf, including the need to mill at relatively shallower depth with potential eccentricity challenges due to decentralized casing,” Stokkeland says.
Since launching Stronghold Barricade, Archer has engineered a new system that has been added to the Stronghold family of PWC and verification systems. The Fortify system tests and verifies the integrity of the existing annular formation in a well.
It perforates the casing, tests annulus integrity, and verifies this integrity using a unique pressure verification system. It then cements across the perforated area. This system has three major benefits:
- The integrated unique pressure verification system has a primary and back up temperature and pressure gauge, confirming the annular integrity.
- Small volume to identify annular integrity, ie. less than three barrels.
- The solid ballseat and the fluid by-pass system limit the circulation of new mud and reduce the impact of thermal expansion.
The Fortify system delivers the final result of a verified permanent annular barrier.