Well construction techniques remain static to some degree. When necessary, engineers look for ways to enhance and improve current technology to provide lower cost and less risk in a variety of drilling applications.

From spud to stimulation, a number of companies are looking at the full drilling cycle to develop tools that can provide a seamless approach to the well construction process.

Engineering RSS performance

For any horizontal well, the payzone begins after the curve is built. Achieving a successful, efficient high dogleg severity (DLS) can exponentially improve the performance and payout of an individual well. Limitations to high build rates include increased friction, bending of tools and added stress on costly BHAs.

When being rotated through these high build rate sections, BHAs experience large bending moments. Fatigue life reduces exponentially with increasing build rate. This can reduce the life of standard BHA components to a matter of hours. Without a method of modeling and tracking fatigue, catastrophic failure and twist-off of BHA components could occur.

The PowerDrive Archer RSS delivers well profiles previously only possible with motors—yet with the ROP and wellbore quality of a fully rotating RSS.

Schlumberger’s PowerDrive Archer high build rate rotary steerable system (RSS) provides the means to drill well profiles with high dogleg severity in order to maximize reservoir exposure and increase the potential for hydrocarbon recovery and combine this with the traditional RSS benefits of increased effective drilling efficiency and superior wellbore quality.

Field trials began in 2008 and after the functionality and reliability of the service proved to be very robust. Due to this systems unique capability in terms of dogleg provision a second stage of field testing was necessary. This supplementary stage was to design and ensure that any bottomhole assembly (BHA) used did not impact the build rate capabilities of the PowerDrive Archer system and that any extra fatigue generated through rotating a drill string through a high dogleg wellbore could be managed.

“For the first time we are bringing fully rotating BHAs to high build rate well profiles,” said Richard Hawkins, product champion, Schlumberger.

The PowerDrive Archer RSS provides full rotation for each of its exterior parts. “As with the entire PowerDrive RSS family, anything exposed to the wellbore rotates at drillstring rpm as a minimum,” Hawkins said. This rotation reduces drag, improves ROP, decreases the risk of differential mechanical sticking, and achieves superior borehole cleaning and conditioning. This reduced friction is especially important when drilling horizontal sections, as the drilling can potentially be extended. Running casing is also significantly less problematic due to a smoother and cleaner wellbore.

Borehole quality is fundamental for drilling optimization. This includes borehole cleaning, tortuosity and wash-outs. With openhole completions, a smooth borehole leads to less chance of borehole problems and key seating.

For cased hole completions, the smooth wellbore with continuous DLS, leads to much easier deployment of completion equipment than with the typically tortuous slide-rotate profile delivered with motors. “In the Eagle Ford, we have seen 20% reduction in wellbore tortuosity,” Hawkins said.

The company has performed comprehensive finite element analysis and detailed strain-based fatigue studies on all the components in the PowerDrive Archer BHA to understand the effects on them when subjected to high doglegs. “We are using fatigue resistant materials and have a predicted fatigue life for the all BHA components,” Hawkins said. Tracking this fatigue life is extremely complex. The company’s Perform Toolkit is provided to automatically track tool fatigue and substantially reduce the risk of failure.

The full rotation is a key feature of the service and is achieved through an advanced control system, which allows the electronic assembly inside the tool to be held geostationary while everything exposed to the wellbore rotates. “Effectively, we measure the exact rotating speed (rpm) of the external drill collar and then use a control system to hold an internal valve at a constant toolface,” Hawkins said. “We then divert a small percentage of the mud flow through the valve to activate the system at the required toolface.”

In field trials, PowerDrive Archer can deliver up to 17 deg/100 ft, from vertical or at any other inclination. “We also accurately measure magnetic tool face, so the wellbore trajectory can kick off on the desired azimuth,” Hawkins said. The tool can drill out the shoe, come off a whipstock or cement plug, stay perfectly vertical, ream or back ream and then kick off accurately with high build rates. The tool can then continue to drill whatever well profile is needed and do this all in a single run. “PowerDrive Archer is a drilling system, one that incorporates bit and BHA design,” Hawkins said.

Hybrid tool provides steerability

The bottom line for high end RSS systems is high cost. The application of RSS in the field has proven its advantage in terms of reducing drilling times and gaining access to the reservoir, however, reluctance to drill with RSS reigns for wells having a high risk of lost-in-hole outcomes.

For conventional directional drilling the use of a mud motor and sliding often provides the means by which operators build curve for a horizontal well. While these tools are reliable and proven through a long history of field use, they come with very little functionality and often result in slow build rates. Neverthless, additional drilling time is preferable to lost time resulting from a stuck tool.

Weatherford International has developed its MotarySteerable tool as a bridge between mud motors, rotary steerables and MWD. The hybrid system outperforms a motor-only approach while providing less risk than an advanced RSS system. “At the low end of the tool box are conventional mud motor tools and directional control systems and the high end includes traditional rotary steerable tools like Revolution,” said Chris Maranuk, new product launch manager, Weatherford International. “MotarySteerable is a tool that essentially combines MWD and mud motor technology to create a low angle assist tool.”

According to Maranuk, the combination of MWD, drilling motors, and RSS experience within a single group of engineers was critical to conceiving this product. “The biggest challenge to making MotarySteerable work was to overcome the barriers between each of the drilling products and remove individual objectives in favor of a greater goal,” Maranuk said.

In traditional oriented drilling, a bent sub is used to point the bit and then turned by the drilling motor to drill the hole directionally. Two sources of rotation are available; one is being actively controlled to orient the bend while the other drills the hole by way of fluid through the drilling motor. Weatherford’s MotarySteerable tool uses targeted bit speed (TBS) to reverse this approach by directly controlling the drilling motor speed instead of controlling bend orientation. The bend is turned continuously with the drill string while motor speed is varied as a function of bend orientation to change the rate of penetration as a function of bend position. “This is the same approach as oriented drilling—point the motor and drill ahead—with the exception that it is done once per revolution of the drill string,” Maranuk said.

A key feature of MotarySteerable system is the ability to change from TBS to sliding without tripping out of the hole. “The ability to use TBS to change directional control has always been a key requirement for this particular system,” Maranuk said. As the system has undergone testing, Weatherford has developed selective updates to enhance the tool’s functionality.

“One of the more interesting capabilities is the “auto inc” feature that allows the user to download a desired inclination and let the system self correct downhole,” Maranuk said. The tool automatically turns on when the inclination starts to wander out of its preset limits and turns off when not required. The tool can be turned off or on through a variety of methods including downlinking through traditional surface initiated pressure pulses or by using various rotational sequences. “Of course, the key benefit of providing the capacity to change from a sliding oriented string to a full 3-D directional rotating string from the surface is the flexibility in terms of operator drilling practices,” Maranuk said.

The MotarySteerable system takes advantage of two proven technologies, mud motors and MWD to create a very reliable robust system. In drilling environments where the system is unable to obtain the desired build rates, one can always stop, orient and then slide using conventional directional drilling techniques, so it offers a very low risk technology. One can expect lower lost–in-hole costs than traditional rotary steerable tools. The key advantage over traditional oriented directional drilling techniques is its ability to offer full 3-D directional control while continuously rotating.

“Not every operator who drills a well in the US needs a high dog leg rotary steerable tool with a full quad combo LWD to drill and evaluate their well,” Maranuk said. “We see a need for this type of service to help compliment those customers who might need a more economical solution with less system performance but yet full 3-D continuous rotation directional control.”

Longer laterals, more frac stages

As drilling operations come to a close, completions operations take effect. Fracing technology has undergone a multitude of advances in recent years, and companies continually engineer this process to provide further performance not only in execution but also in outcomes.

Baker Hughes Inc. recently completed a record-setting 40-stage frac job in North America’s Williston Basin, which is known for extremely long laterals—some in excess of 9,000 ft. (2,743 m).

On average, Baker Hughes’ FracPoint completes wells in the US in 19 stages, which is up from five stages in 2006. “We expect this number to approach 30 by year end,” said Matthew Kebodeaux, Product Line Vice President, Baker Hughes. The company’s latest achievement was delivered with its FracPoint EX-C system. Operators performing plug and perf operations to achieve their desired number of stages can now switch over to openhole multistage fracturing, which is more cost effective because of the rig time savings.

“Even though every shale formation is different, there is a growing consensus in the industry that more stages equal more production so our clients are continually requesting increasing numbers of stages per well to shorten the frac spacing interval, improve fracture efficiency, and increase their production on a per well basis,” Kebodeaux said.

Baker Hughes’ latest version of FracPoint, the EX-C, provides the ability to fracture up to 40 stages in series with continuous pumping operations using 1/16-in. increments in ball and seat sizes. In addition, the FracPoint EX-C system does more than just increase the number of available stages, it also allows the use of larger ball seats on wells that do not require a full 40-stage system, which allows for increased pump rates during the frac and reduced pressure losses during production.

The FracPoint EX-C system uses a combination of patented features, which include double barrel seats and collapsible ball seats. The double barrel seat has two parallel bores that permit a substantial increase in flow rate over a single ball seat when deploying smaller size balls. The collapsible ball seat allows the contact area of the seat to change once the ball lands, which in turns increases the load carrying capacity of the seat and allows the system to meet the pressures ratings required. “Baker Hughes has been deploying 24-stage FracPoint EX-C systems since September 2009, so the concept and functional performance of the tool is proven,” Kebodeaux said.

The results of the first completions performed with the 40-stage FracPoint EX-C system have been very favorable. The company is embarking on its next improvement of this system with the release of its IN-tallic Frac Balls, using controlled electrolytic materials technology, which is an engineered material that provides high strength while disintegrating in a controlled manner in the presence of brines and acids.

The company expects to deploy FracPoint EX-C technology in every basin where high quantity openhole multistage completions are used. As the industry trends toward longer laterals, providing more frac stages in less time has become the goal of service companies like Baker Hughes. “While these initial 40-stage FracPoint jobs have saved our clients an estimated 5 days per completion over a 40 stage plug and perf job, the key to delivering real value for our clients is in increasing lateral lengths and improving fracture efficiency, thereby reducing the spacing between wells,” Kebodeaux said.

Beyond status quo

“When Packers Plus began doing openhole fracturing in 2001, the industry believed that 5-8 fracture treatments could effectively drain a 1,000 m (4,000 ft.) horizontal well,” said Dan Themig, President and CEO, Packers Plus. The company’s StackFRAC HD is an innovative approach that challenged the status quo on what is required to effectively drain tight gas and oil resource plays. The industry has quickly applied this technology to move to 20 fracture treatments per well, but the HD systems from Packers Plus—including its newly launched QuickFRAC system—are now moving to 30-60 fracs, a number—unfathomed 4 years ago. “We believe this is the future of development for shale gas and oil,” Themig said.

Packers Plus QuickFRAC multi-stage batch fracturing system enables simultaneous stimulation of multiple stages (group) with a single fracture treatment at surface. (Image courtesy of Packers Plus)

This technology also applies to conventional plays, where historically the approach has been “downspacing” in drilling patterns from 640 acres to (eventually) 10 acres. StackFRAC HD allows 10 acre drainage patterns with fewer wells at surface, greatly improving economics, but also greatly reducing water usage and environmental concerns.

Unlike conventional cemented casing completions, which plug natural fractures and attempts to restore connection to the formation with fracturing, the StackFRAC HD system is designed to allow stimulation of openhole horizontal wells. This allows the rock to produce from both natural and induced fractures. “Production comparisons on the two methods show that openhole completions (StackFRAC) outperform cemented completions from 25 to 70%, not just in initial productivity, but also similarly improving ultimate recovery,” Themig said.

In cemented completions, the fracture is forced to initiate at perforations, rather than allowing them to initiate in natural weakness of the rock. StackFRAC HD allows the fractures to both initiate at a weakness in the rock rather than at perforations. Thus, it allows the fracture to initiate and propagate at the same point, greatly reducing tortuosity. In addition, StackFRAC HD allows for accurate displacement of proppant without overdisplacing. “We are seeing a massive shift and acceptance that openhole fracturing produces much better ultimate recovery of resources and in many cases can allow the reduction of water usage by as much as 50% per stage,” Themig added.

StackFRAC HD also greatly reduces the time required to stimulate a well. Instead of utilizing wireline pump down bridge plugs and coiled tubing, resulting in excessive time to perform fracturing, StackFRAC HD allows a ball to be launched and pumped downhole on the fly, seamlessly moving from stage to stage. QuickFRAC has allowed for even more time savings by fracturing multiple isolated stages with a single fracture treatment from surface. “Our record using QuickFRAC technology has seen 23 stages pumped in less than 10 hours,” Themig said. “Conventional methods treating 2-3 stages per day, would have taken 7-10 days.”

Looking ahead

At the end of the day, there are countless opportunities to cover the many advances that occur in downhole technology. The systems discussed here represent a fraction of the output from a multitude of engineering teams. By observing both older and newer ways of improving drilling efficiencies, the industry will continue to hone current technologies to improve on very specific parts of the process and to provide the widest range of applications throughout the world’s oil and gas producing regions.