Hybrid CT Rigs Enter The Unconventional Market

?Coiled tubing (CT) drilling is moving into the unconventional market. Several companies are combining drillpipe to the process to provide a hybrid rig that can drill conventionally while providing the benefits of CT ina dual-purpose setup.

Calgary, Canada-based Xtreme Coil Drilling, which now is headquartered in Houston, recently signed a multiyear contract with a new customer for its XTC 500 Coil Over Top Drive (COTD) model. This fit-for-purpose model features the latest AC variable frequency drive equipment designed to contend with deep horizontal resource plays. When the rig is completed in 2Q 2011, it will bring the company’s fleet to 17 rigs and will be the second rig contracted to work in North Dakota’s Bakken formation.

The XTC 200DTRPlus Rig #1 drilled a deep coil horizontal re-entry well in Saudi Arabia. (Images courtesy of Xtreme Coil Drilling)

The XTC 500 has a broad application in the horizontal shale plays. The rig features two 1,600-hp mud pumps that provide the pumping capacity needed for most horizontal applications. The AC rig is rated at 500,000 lb hook load capable of drilling to 21,500 ft (6,553 m) using 4-in. drillpipe or 15,000 ft (4,572 m) with 5-in. drillpipe in horizontal applications. It has an automated pipe handling system capable of drilling with double stands of 45-ft (14-m) joints. The biggest advantage with Range III drillpipe is that it allows faster tripping out of hole with one-third fewer connections, which means one-third fewer total joints to inspect.

The rigs are capable of drilling to 10,000 ft (3,048 m) with 3½-in. coil. With its 5,000-psi circulating system, the XTC 500 provides adequate volume, pressure, and redundancy for drilling with CT and in re-entry wells.

Setting its sights

Xtreme’s technology has been on the market for about four years. According to Rod Uchytil, president and CEO, “Our focus has always been international.” Based in Canada, the company targeted the US first, then Mexico, and Saudi Arabia. While the company’s activity in Mexico has slowed, its recent move into the unconventional market is promising, and it continues to find a great deal of success in Saudi Arabia. “We’ve got a joint venture in Australia as well, which will be more of a coalbed methane application,” Uchytil said.

The goal for Xtreme is to parlay its success in shallow drilling environments to extend its reach with large coil to 10,000 ft or more. “Again, I think the automation we’ve developed has really helped us to get there,” he added. Xtreme holds the record for the deepest well drilled with 3½-in. OD coil at 9,954 ft (3,024 m).

According to Uchytil, the XTC 500 rigs operate well as conventional rigs. The modular design allows the rig to move quickly. In addition, its high level of automation allows the operator to compete with “tier one” AC electric rigs. “And then you have coil as an add-on,” Uchytil said.

The coil provides a dual purpose that allows for drilling or for use in other well-servicing applications. The drilling capacity depends on the well profile such as with underbalanced needs, or if the well path intersects different kinds of hard and soft formations. “We have had good success in both,” Uchytil said. The driver for designing the XTC 500 was to reduce time on the well and to reduce operating costs.

For underbalanced operations, CT perhaps is one of the best tools available due to its closed-loop status without the need to make connections. “If you are truly flowing the well, that allows you to make a lot more progress,” he said. “You are drilling a faster and safer well.”

For the unconventional market, Xtreme’s deeper coil capabilities can be valuable when operating through cleanouts after fracing. Xtreme currently is not working in the Marcellus, but the company hopes that will change due to a letter filed by the Pennsylvania Department of Environmental Protection on July 13, 2010, suggesting the required use of either a snubbing unit or a CT rig for all post-completion works. The ruling came as a reaction to a recent blowout that occurred during the cleanout phase of a well in that region. “Once the well has been completed and fractured, you have to use something that can control the pressure better,” Uchytil said.

In addition to the company’s move into the Bakken, it has one rig going into the Eagle Ford at present and is looking to add more.

The company has plans to build up to four new XTC 500s, and is scoping the market for its XTC 750. The XTC 500 and the XTC 750 are similar rigs. The main difference is the XTC 750’s increased substructure height, which allows it capacity to run 10,000-psi BOP equipment for standard drilling operations. “This is more for the conventional application than the coil application,” Uchytil said. “The upgraded equipment will allow us to get into deeper prospects.”

AC electric versus hydraulic

COTD rigs feature an enclosed driller’s console with fully automated drilling capa­­­­bility.

Xtreme has developed one advantage over similar hybrid rigs and conventional rigs – AC variable frequency drive injectors. Traditional injectors are rated to a maximum of 120,000 lb. Xtreme’s XTC 500 uses a 200,000-lb injector. Moving to AC from of hydraulic provides a finer control that allows more functionality throughout the drilling process.

“One of the things that we have done is to develop an automatic milling program for re-entry wells,” Uchytil said. The company developed a program that can mill through casing more efficiently while leaving a smoother window. “We have realized up to a 50% time saving in that application, and we are not experiencing any problems coming in and out of the window,” he added.

Using the PLC programming of the rig control system, Xtreme has developed an algorithm that provides a time-drilling approach as opposed to putting more weight on the bit to mill the casing. “We are using the analogy of a lathe and how that tool is used to cut through steel,” Uchytil said. The company’s AC injector offers more

control than one operating on a hydraulic system. “If you want to advance one-quarter inch per hour, you can have that kind of control,” he added.

While Xtreme’s unconventional activity in North America is promising, its XTC 200DTRPlus is setting the pace for re-entry projects in Saudi Arabia. Since 2010, the company has used two COTD XTC 200DTRPlus rigs to drill horizontal re-entry wells. The process uses coil to mill a window through one or more sets of casing, build curve sections, and drill the horizontal sections in underbalanced conditions. Patents are pending for the technology, which was developed specifically for this project.

New horizons

The company is working for Baker Hughes through an integrated project with Saudi Aramco. “These re-entry wells are a 100% coil application,” Uchytil said. The wells can have up to 6% to 8% H2S and require 10,000-lb well-control equipment. The process is allowing Xtreme to drill through and actually flow the sour environment. The concept is unique based on the fact that the rigs are carrier mounted on a four-leg hydraulic jackup structure. “We took an offshore structure concept and applied it on land, which allows us to jack up, skid in and out, jack down, and move,” he said.

The system is trailer mounted, so it can be moved as one piece. “It is making a huge difference. Our last equipment move was performed in 24 hours over a 75-mile (120-km) distance,” he said. This rate is impressive considering that rig moves prior to the XTC 200DTRPlus ranged from seven to nine days, most of which was consumed by dismantling/reforming a conventional rig substructure.

Xtreme developed its XTC 750 concept for this type of project. “Our customer needed a rig with the capacity to drill to 14,000 ft (4,267 m) with drillpipe, which would allow for setting larger casing strings and drilling larger hole sizes,” Uchytil said. The challenge was to drill horizontally through the reservoir in underbalanced conditions. “We had to be able to run coil as deep as 20,000 ft (6,096 m).”

To date, the customer has seen a vast improvement in production from these wells as a result of drilling underbalanced with coil. In addition, an ongoing study is being performed to determine whether production could be improved by drilling grassroots wells in the same fashion rather than reserving the technique for re-entry wells only.

CT technology was developed with live wells in mind. Before this technology was combined with conventional rigs, it was used primarily in live-well interventions. “I think the industry has always been aware of these benefits; it was just finding the right application,” Uchytil said.

The driver behind the success of Xtreme’s underbalanced horizontal drilling is its high-powered AC electric injector and automation systems. The company currently uses 0.224-in. wall thickness on its 3½-in. coil – one of thickest in the industry. “Your injector has to be able to straighten and bend that pipe and move it out of the hole,” Uchytil said. Xtreme’s injector was designed in house using outsourced companies. “It was about a 17-month development time until we had it in use in the field,” he said. The injector is rated up to 200,000 lb, which is nearly double what is conventionally available in the industry today.

Because the injector is AC electric, it provides much more control than a joystick and hydraulics, which often can be jerkier. With hydraulic controls, pump pressure differential increases can occur as the driller stacks weight on bit. Without the ability to release it fast enough, these instances can cause stalling and can damage the motor.

“With AC electric and our software algorithm, you’ve basically got an auto-drilling program,” Uchytil said. The additional level of automation allows drillers to enter parameters for upper and lower limits in the PLC system. In addition, the computer has much faster reaction than a human operator when regulating how much weight is applied. “The injector is designed to run pipe into the hole, and by setting it with specific parameters, the driller tricks the unit to behave more like a conventional rig where the operator holds back weight and just slacks off enough to get it to drill,” he explained.

As the XTC 500 moves into deeper basins, the AC injector can improve performance in harder formations. “In these harder formations, you’ll go from 100 ft/hr to 10 ft/hr and then back to 100 ft/hr (30 m/hr to 3 m/hr), and the computer automation is able to react fast enough to allow you to continue to drill – and to drill efficiently – through these harder and more interbedded formations,” Uchytil said.

According to Xtreme, furthering the levels of automation in the drilling process is the most important step for advancement. Based on its Saudi Arabia experience, the company can drill in the hard carbonates in this region at a rate of up to 1,000 ft/day (305 m/day) with an auto-drilling technology. “That is basically without having a person on the brake; it’s an automated process,” Uchytil said. AC electric provides an interface with the computer, which in turn allows infinite control and the ability to distribute the power amongst the rig’s components.

With the improvements made on the coil side of the business, Uchytil asks, “Is there something that we can do better with the conventional components of our hybrid rig or additional levels of automation that would improve efficiencies on that side as well?