Nearly 11 years after Weatherford first commercially deployed drilling-with-casing, the service company is still testing the limits of where and how the technology can be helpful when it comes to overcoming wellbore instability. Jennifer Pallanich catches up with Weatherford’s Steve Rosenberg to discuss applications of liner drilling.
Liner drilling has definitely evolved since its first commercial deployment, says Steve Rosenberg, Weatherford’s US region product line manager for drilling-with-casing. Most of the advances have been with respect to the liner tools: expandable liner systems, expandable hangers, pressure-balanced liner systems, retrievable and steerable liner systems, and drillable casing drilling bits.
Weatherford’s latest contribution in the liner drilling arena are the PDC drillable casing drilling bits, Rosenberg says. Weatherford created the first PDC drillable casing drilling bit that can be drilled out with a conventional PDC bit, eliminating a dedicated bit for drill out, he says. The first such application was offshore Malaysia last year, when a Smith 121/4 MSI 516 PDC bit drilled out Weatherford’s 133/8 by 16in four-bladed Defyer DPA drill bit in 117ft water depth.
The Smith PDC bit ‘drilled through the casing bit in 12 minutes and went on to drill the required 1488m of new hole,’ Rosenberg says.
Using Defyer DPA drillable casing drilling bits, which are made with 80% less steel in the bit’s drill out area than conventional bits to enable drill out with a conventional PDC bit, can eliminate the need for a dedicated drill bit or dedicated trip to drill out a bit, which can save anywhere between six hours and a day, depending on depth, Rosenberg says. Since that first Asia Pacific drill out of the Defyer DPA, the Defyer DPA bits have also been drilled out in South America and the Gulf of Mexico as well as onshore in the US.
Steel wall cake
Rosenberg describes how Weatherford used liner drilling when there was a lost circulation interval offshore Indonesia in the Lower Baturaja limestone formation, a carbonate reef structure known for lost circulation conditions. Operator CNOOC had three sidetracks, trying to mitigate the lost circulation and hole instability in the formation in the Banuwati field, originally discovered in 1979. CNOOC and Weatherford recommended drilling the 8.5in hole section of the A-3 well with liner to get to total depth because it ‘would isolate the problem zone in a single trip’, he says.
conversion ball, convert DrillShoe, drop hanger setting ball, set hanger. 3. Expand ball
seat and release setting ball. Begin cement job, pump displacement, release drill pipe
wiper dart and latch wiper dart in liner wiper plug. 4. Land liner wiper plug in landing
collar. Check float valves. 5. Set and test liner top packer. 6. Pick up liner setting string
and reverse out cement. Pull out of hole.
The liner is already in place, so the drillers don’t have to count on loss circulation material or chemical treatments ‘which may or may not be successful. With liner drilling, you have “steel wall cake”,’ Rosenberg says. ‘You isolate your zone with your planned casing, and you’ve got, for lack of a better word, steel, isolating your lost circulation.’
CNOOC and Weatherford planned and executed the 2007 job in the Banuwati field in 71ft water depth in about a month.
‘Basically, they drilled conventionally with an 81/2in bit to a depth of 9968ft measured depth and the hole had 67° of inclination using an 11lb/gal synthetic drilling fluid,’ Rosenberg says. At that point, the conventional drilling assembly was pulled out and the liner drilling assembly was used, which included the Defyer 7in by 81/2in drillable casing bit.
Weatherford ran 43 joints of 7in, 26#, 13Cr L-80 Vam Top casing from the Bohai IV jackup. Direction was a concern in this job, Rosenberg says, adding it was necessary to maintain 60° of inclination while drilling the 81/2in section from 9968ft to 10,317ft. ‘We only increased inclination 4° and azimuth changed an accomplishment he attributes to the stiffness of the 7in liner.
Along the way, at 10,110ft, there were severe mud losses, to the tune of 600bbl/h. At that point, Rosenberg notes, liner drilling continued to 10,317ft MD, losing total returns, but Weatherford was able to ‘keep the backside full with 8.6lb/gal water-based mud and 11.8lb/gal syntheticbased mud and seawater.’
The success, he says, came from keeping the annulus full with the mud and seawater by using the trip tank pump.
‘When drilling-with-liner or casing versus conventional drilling, in event of losses through the bit, you’re able to Keep up with annualr fluid losses with a trip tank pump or some other dedicated annular pump because you have a narrower annular geometry as compared with geometry seen in conventional drilling operations,' Rosenberg says. "The pump was tied into the rig's trip tank, and that pump pumped the required amount of fluid into the annulus to maintain a full level. Because of an inherent larger annular geometry, this would not be possible in conventional operations.'
During this job, he notes, Weatherford made use of a mechanical ball seat instead of a pressure-activated hydraulic ball seat to remove the liner hanger setting ball form the flow path because the service company wanted to reduce the amount of pressure the formation was exposed to. Releasing the liner-setting ball was ‘a mechanical event,’ he says, and the first time Weatherford had used that in a liner drilling application.
‘The job went down very well,’ he says, noting the technology saved the operator about $1 million. Drilling the 349ft section took 11 hours with an average ROP of 32ft/h.
In another run, an operator was dealing with ballooning issues, which were preventing drilling with conventional methods. Rosenberg says the 2011 job, in 97ft water depth in the central Gulf of Mexico for an unnamed operator, is the first documented case of using liner drilling to mitigate wellbore ballooning, which can be misinterpreted as a well control event.
Ballooning itself, he says, isn’t catastrophic as it is related to the plasticity of the formation. Confusion can arise because when fluid is pumped, the formation will take the fluid, and when the pump pressure is released, the formation gives back that fluid to the wellbore. If this leads the driller to misinterpret the influx as a well control event, the response would likely be to weight up with mud unnecessarily to contain the misdiagnosed kick. However, weighting up too much may result in the operator ‘short setting’ the casing and not meeting construction objectives, Rosenberg explains.
The ballooning interval was evident at 10,900ft, Rosenberg says, and it would not be possible to drill with conventional methods to the planned TD.
‘What liner drilling does is eliminate many of your surge and swab effects because pipe does not have to be tripped in or out of the hole,’ he says. Eliminating the surge and swab effect of tripping pipe elimates the trip margin required for pulling out of hole and additionally reduces losses attributed to tripping pipe in the hole, he adds.
The revised drilling plan called for setting the whipstock at 9516ft in existing 95/8in casing, drilling a conventional 81/2in hole, and building the angle to 60° while drilling to to 10,982ft. At that point, the conventional drilling assembly came out, and a 7in x 95/8in liner with 7in x 81/2in Defyer DPC 513 drillable casing drilling bit was run.
‘We maintained the hole inclination of 60° and the azimuth of 143° over the 337ft liner drilled interval,’ Rosenberg says, noting liner drilling went down to 11,320ft. He says no wellbore ballooning was evident on connections. The liner top packer was set and subsequent logs showed the casing bit was at an acceptable TD, eliminating a contingency 5in liner, he says.
There were partial fluid returns.
‘Attempts to convert the shoe were unsuccessful . . . because we were not pumping fast enough to effectively clean the hole, and we think solids fell in around the bit, precluding the ability for the bit’s PDC cutter blades to displace into the annulus,’ Rosenberg says. ‘Because hole cleaning was not under optimal conditions, we could not convert the blades to the annulus.’
He says pumping any faster could have posed the potential for lost circulation, thereby hurting the chances of getting to an acceptable depth. The drilling from the mat cantilever jackup reached acceptable depth, however, so the drill shoe didn’t have to be drilled out.
‘When used, it has profound ramifications,’ Rosenberg says of liner drilling. Weatherford has carried out nearly 20 of the roughly four dozen liner drilling jobs that have been done since the technology’s inception. OE