Casing drilling comes of age

Drilling with casing continues to draw interest for its ability to overcome troublesome formations. Jennifer Pallanich reviews Weatherford’s recent applications of the technology offshore Brazil and West Africa.

Weatherford carries out its drilling with casing (DwC) work using the Defyer Series drillable casing bit, which drills like a conventional PDC bit, in medium to medium-hard formations. The premium version of the series is the Defyer DPC, formerly known as the Drillshoe III; the Defyer PDC is designed to drill in formations with confined compressive strengths to 15,000psi.

A pressure-cycled, PDCdrillable piston displaces PDC blades into the annulus after reaching TD. A thin layer of tungsten carbide coats the steel and PDC blades to provide resistance to erosion and abrasion during drilling. The cutters allow DwC in firmer and more abrasive formations than previously possible, according to the service company. Following the cementing, a conventional PDC bit can drill through the Defyer DPC.

The Defyer PDC is Weatherford’s design meant for drilling in formations with confined compressive strengths to 15,000psi.

Some reasons for DwC, of course, include the reduced trip times, placement of casing to design depth through problem formations, reduced potential requirement of contingency casing and reduced initial surface casing size because it can go deeper.

‘With drilling while casing, we’ve got control of the well through optimized hydraulics, even though you’re not getting these returns back.’ Scott Beattie

The first 133/8inx17in Defyer DPC job, drilled offshore West Africa in 102ft of water in September 2008 was ‘a massive success,’ says Scott Beattie, Weatherford’s global business unit manager for DwC. The operator anticipated heavy fluid losses in the 171/2in hole section and decided to drill in the 133/8in casing to TD at 673m using the Defyer DPC519. The complete section of 418m was drilled in 26 hours with an average rate of penetration of 21m/h. As anticipated, the entire hole section was drilled with total losses. One of the benefits of drilling with casing in this instance was the ability to keep the annulus full of fluid, thereby creating a floating mud cap. In this application, using DwC saved the operator 24 hours of rig time and likely eliminated days of fighting lost circulation, according to Weatherford. While drilling the same hole section in the prior well, the conventional BHA was lost in the hole, resulting in abandonment, Beattie says. Based on the performance of DwC in this well, the client plans to drill all subsequent wells in the region with the Defyer DPC, according to Beattie.

‘With drilling while casing, we’ve got control of the well through optimized hydraulics, even though you’re not getting these returns back,’ Beattie says.

Not much later, in February and March of this year, Weatherford did a similar job for Petrobras offshore Brazil. João Carlos Ribeiro Plácido, technical consultant at CENPES, says Petrobras decided to qualify this technique to use in wells with instability and lost circulation problems. He says the field chosen for the test was one located in 92m of water where the offset well had 10 days of NPT trying to solve lost circulation problems.

This job entailed two firsts: the first run of the new Defyer DP in conjunction with the first 16in drilling with liner system in a highly vugular limestone formation in 150m water depth. This formation, which resembles a dry sponge, presents a challenge in that it’s difficult to predict formation strength and the volume of fluid loss. The drilling team ‘knew from the get-go’ that there would be fluid losses if this segment were drilled via conventional methods, Beattie says. In fact, previous efforts to conventionally drill the 114m section of the 171/2in wellbore had taken 35 days, primarily due to 100% fluid losses. Drilling with liner was not without incident either, according to Beattie, as after drilling out the 20in shoe, there were two instances of sticking the liner within the first 2m, which is attributed to the unconsolidated rubble zone. It was necessary to clear up the returns that had accumulated downhole before it was possible to drill the complete section with a controlled ROP, Beattie says. Weatherford used a 171/2in bit with 16in deepwater liner system – it was an ‘absolutely tiny annulus,’ Beattie says – and drilled 114m in 18 hours.

Drilling began with a water-based mud system but was quickly changed to seawater to keep up with fluid loss and also reduce the ECD, according to Weatherford. The annulus was kept full from the trip tank and the section was drilled at a controlled ROP of 5m/h even though the bit was capable of far greater penetration rates. Average weight on bit was 5000-10,000lbs with rotary speeds between 70 and 80rpm.

The liner drilling technology performed well, Plácido says.

Petrobras plans to have Baker do three field tests with that company’s EZCase technique onshore in a field with lost circulation in a carbonate interval, Plácido says. He also says Petrobras is considering using 18in liner drilling in the same field the Weatherford technology was used with a 16in liner. In general, he adds, Petrobras is considering this technology for the pre-salt area to overcome salt formation instability due to high creep rate.

Subsea system

Weatherford is developing a new subsea DwC system called SeaLance under the sponsorship of Italian operator Eni. In late June, the service company announced the award of an innovative technology agreement from Eni to work on SeaLance.

Paolo Nunzi, drilling completion and work over manager at Eni UK, shared some details on the technology and Eni’s drivers behind the development of a subsea DwC system. ‘The technology will allow for the 20in casing together with a subsea high pressure wellhead housing to be drilled to TD, latched into the low pressure wellhead housing without rotation, cemented, and disengagement of the running tool before the string is pulled out. The casing drillbit allows for easy drill out by any standard oilfield drill bit on the following BHA run,’ he says.

‘Deepwater wells have been drilled the same way since deepwater frontiers were first explored.’ The industry has been focused on reducing drilling risk, which is admirable but Eni believes successfully pushing the envelop, ‘can only go so far without changing the method, which this system does.’

Eni believes the system will reduce the time it takes to install the 20in casing and high pressure wellhead housing and will enable surface casing seats to be set deeper in line with the hydrostatic pressure profile of deepwater wells. This will enable a more efficient well design while improving safety, managing risks and mitigating hazards.

To expand on this, Eni explains that the introduction of DwC technology in deepwater will allow the company to manage shallow hazards, like shallow gas, shallow water flows, losses, caverns, collapsed holes, tar, and rubble zones, adding that ‘because the casing is always on bottom, problem zones are put behind casing by default’. The annular space in a DwC system is also much less than conventional drilling and allows any flows to be dynamically controlled. By manipulating the hydraulics, the ECD on the return flow up the annulus can be managed, allowing ‘the operator to dynamically kill a well and continue drilling to a deeper casing seat than may have previously been possible,’ according to Eni. The idea being that this method ‘will allow new previously unattainable casing designs to be planned, maximizing hole diameter and saving contingency strings for when they are more critical at deeper depths closer to the targeted reservoir,’ Eni elaborates.

Weatherford says the SeaLance system will allow the remaining casing seats to be pushed deeper into the wellbore and that the technology advancement will further enable applications in sub-salt plays.

The technical agreement between Eni and Weatherford calls for three basic components that comprise the system, which have been in development for around a year and a half: the casing drill bit, the drive mechanism and the retractable shoe joint. The drive mechanism will use a running tool which will lock into a setting sleeve below the wellhead, through which casing tension will be held as well as offering a torque path through from drill pipe to casing and hence down to the casing drill bit, according to Eni. The entire string will then be rotated and new formation will be cut via the casing drill shoe. The retractable shoe joint has two functions. It allows for the activation of a circulating valve which will allow the cementation process through an avenue other that the drill shoe. It also allows the casing to telescope into its self at a desired TD, so that the high pressure wellhead housing is not rotated inside the low pressure wellhead housing. Eni elaborated that these features will activate by a hydraulic conversion activated by a ball drop.

‘This is very much a vertical system,’ Beattie says, noting that if it is used in the Gulf of Mexico, it would probably be used for the first two casing strings before the wellbores went directional.

Eni expects SeaLance development to be completed by year-end and has said it is considering a few potential deepwater project applications for this system in 2010, but it will come down to the geological data and rock strength analysis related to the superficial formations where the 20in casing will be set.

Weatherford hasn’t actively marketed the SeaLance system yet, Beattie says, adding: ‘We want to complete the trials and prove the technology in a controlled manner but are extremely confident.’ He does expect to see the technology lead to a ‘glut of really good jobs’.

Beattie says Weatherford performed most of the engineering work out of the Houston office. ‘The good thing about today’s engineering is you can do a lot of virtual tests,’ he says. But the service company also carried out testing on their Technology & Training Center rig in Houston.

The project team has learned quite a bit during the development cycle, according to Eni. One of the more surprising findings was relating to vortex-induced vibrations (VIV), typically a major concern when running large casings in deepwater. ‘When running casing conventionally VIV can be an issue as the sea currents induce vibrations which can increase in frequency, potentially leading to a catastrophic failure at the connections, this danger remains as casing is run in the hole. Although the issue still remains while running casing trough the water column to bottom prior to DwC the introduction of the SeaLance will allow the casing to be rotated thus shedding the vortices around the casing and minimizing the potential of failure.’

For the time being, Weatherford will offer SeaLance in the 20in casing size. Beattie says it would likely take about a year of engineering and testing on another size before the service company would be ready to go larger. ‘We see the value in other casing sizes. Larger casing sizes, rather than smaller,’ he adds. OE