[Editor's note: A version of this story appears in the July 2020 edition of E&P. It was originally published on July 1, 2020. Subscribe to the magazine here.] 

In the high-volume, demanding drilling environment of North America land wells, rotary steerable tools (RSTs) have struggled to find their place. Where drilling success is measured by ever-increasing lateral lengths with continuous downward pressure on cost per foot, the risk profile associated with running a complex RST— together with its litany of potential failure modes— causes many operators to think twice. As a result, positive displacement mud motors still get the nod in many applications, despite the inefficiencies they bring to the drilling process and the negative impact they have on borehole quality.

D-Tech Rotary Steerable has simplified every step of the process—the tool’s design, the ease of wellsite operations, how maintenance and tool turns are performed, and how employees interface with clients to help operators meet their goals and drive costs downward.

Simplicity in tool design

Fewer moving parts (and fewer parts overall) have proven to improve tool reliability by removing failure points that can cause increased downtime. With only 10 moving parts made with the highest quality materials and components, the average 12-ft to 13-ft robust assembly is one of the shortest, most streamlined rotary steerable systems on the market. The short length also improves downhole tool performance by reducing the risk of getting hung up while navigating through challenging wellbores and extreme doglegs.

When evaluating failure modes in downhole tools, human error is always a category that stands out. Before a D-Tech system is shipped to the well site, it is programmed in house and preconfigured for the client’s intended well profile and application. Upon arrival at the rig, it is ready for immediate use, simplifying prejob testing, eliminating the risk of wellsite programming errors and minimizing the time required for tool pickup and bottomhole assembly (BHA) configuration.

Tool collar fatigue is another common failure mode. Systems with collars with localized stress points often required for data port access or to secure internal assemblies might exhibit failures in tough drilling environments found on land. These failures can be exacerbated by drilling with severe stick/slip through periods of high-frequency torsional oscillation. The D-Tech RST design utilizes a monobore design without external data ports or other stress points in the collar, thereby eliminating the potential for BHA failure caused by the formation of fatigue cracks.

Design features

The D-Tech RST uses push-the-bit technology, which delivers responsive steering performance, requires only a small amount of electrical power and minimizes wear on internal components. Push-the-bit systems apply a controlled side force to the borehole, pushing the drill bit in the opposite direction to achieve the required wellbore trajectory control. The side force is generated hydraulically by the bit pressure drop defined by the bit nozzles. A small percentage of the overall mud flow through the drillstring deviates to the hydraulic pistons of the D-Tech RST.

Developed as a fully rotating system, the assembly is ruggedized for high vibration and shock, can tackle abrasive formations that are known to be hard on tools and is compatible with challenging mud systems. With integrated power generation, the low-power requirement also requires less reliance on lithium batteries and eliminates the risk of downhole venting. This, in turn, increases the time that the tool can spend downhole or is deployed, minimizing HSE concerns and reducing limitations on time below the rotary. The full-rotational capability reduces the potential for stuck pipe and lowers the need for excessive reaming.

Pinpoint wellbore steering control is delivered by a three-axis, near-bit directional package that is positioned 4 ft from the bit. Consistent, predictable build rates help the tool drill high-quality wellbores with minimal tortuosity that can provide better zonal isolation, reduce well delivery costs and improve a well’s production over the long term.

Improved rig site communication

During drilling operations, tool performance is continuously monitored by engineers in D-Tech’s real-time operations center. Effective communication between the operations center and the rig increases drilling performance, drives up tool reliability, reduces undesirable tool damage from exceeding recommended specifications and minimizes the need for on-site personnel.

Although it will not completely eliminate damaging vibration, data show that having a performance engineer on site or monitoring operations through the 24-hour center can increase tool longevity and reduce nonproductive time. At least 19 incidents have recently been avoided by having real-time support involved that could have otherwise resulted in an unplanned trip. Basin-specific knowledge of lithology and formations helps minimize vibration and vibration-related failures by communicating drilling and BHA recommendations to the rig and providing input on selecting the most suitable drilling parameters to minimize vibration and maximize rates ROP. 

Minimizing downlinks

The RST continuously records inclination and azimuth, which is used to maintain directional control and allows the operator to drill to a target and consistently remain in the zone. By minimizing the mass of the internal directional control assembly, the system enables directional response to any drillstring speed variations without negatively impacting the well placement accuracy.

The scalable architecture of the D-Tech RST, which allows it to be paired with any MWD system and drill bit, utilizes the same, centrally mounted control electronics assembly across all tool sizes using suitable adapter kits. The low-power consumption eliminates the need for highpower electronics components and provides an inherent reliability advantage. An integrated power generator provides the energy required to operate the system with minimal pressure drop and flow restriction to enable an unlimited, reliable source of power. Communication with the tool is achieved using an efficient surface flow-rate modulation while drilling without affecting ROP.

An operator drilling in the Permian Basin wanted to increase ROP and overall efficiency while reducing costs associated with drilling a challenging interbedded application. The customer worked with the D-Tech team to choose the optimal BHA, which included the RST675 with next-generation drilling software.

The tool’s improved inclination and azimuth capabilities allowed the RST to drill 10,128 ft in 47.25 drilling hours. They were able to reduce the number of downlinks to 14 while drilling, reducing downtime, manual corrections and tortuosity. At an average of 214.34 ROP, the operator reached total depth in one run, all while staying in zone 100% of the time.

Recent modifications to the D-Tech tool, now in its sixth generation, have focused on further improving system reliability and ruggedness along with new features to increase tolerance to higher downhole temperatures and steering accuracy at high-rotational speeds including:

  • Reduced response time to drillstring speed variations to minimize toolface offset errors; • Increased maximum downhole rpm to 330 rpm;
  • Implementation of high-torque rotary connections for demanding land drilling BHAs;
  • Introduction of proprietary wear-resistant pistons for highly abrasive formations;
  • Overall system ruggedization to address high- frequency torque oscillations; and
  • Increased tolerance to high concentrations of lost circulation material.

D-Tech works to reduce tool complexity, engineer out failure mechanisms and improve ease of use. For operators, this means better performance in demanding drilling environments, a further reduction in drilling costs and an overall increase in well productivity through borehole quality improvements.