SPE 169348
Advancements in Powered Rotary Steerable Technologies Result in
Record-Breaking Runs
Hernando Jerez, SPE, and Jim Tilley, SPE, Halliburton
Copyright 2014, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Latin American and Caribbean Petroleum Engineering Conference held in Maracaibo, Venezuela, 21–23 May 2014.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been
reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its
officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to
reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
Abstract
Drilling operators continually experience increasing pressure to achieve all objectives safely and at the lowest cost. Powered
rotary steerable systems (RSS), applied within the correct drilling environment, can improve rate of penetration (ROP), lower
risks, and reduce non-productive time (NPT), which can decrease drilling costs.
Using through motor telemetry (TMT) technology, a wired motor with a hollow rotor and flex shaft, allows a connection
between rotary steerable systems (RSS) and logging while drilling (LWD) downhole tools. A conductor passes power and
communication through the motor to operate and steer the RSS. The wired power section uses a uniform wall thickness stator
design that reduces heat production and retention. It also delivers higher rev/min and torque directly to the RSS and bit.
Using the TMT powered RSS not only has improved ROP, but has also mitigated stick-slip vibration and reduced NPT. The
NPT improvements have been identified in areas, such as slip-stick vibration, drill string failures, drill string torque
variations, casing wear, and rig equipment failures.
Early planning and risk assessment have also been key. Experience across the globe, both on and offshore, are presented
to show the benefits of integrating advanced drilling technologies, such as TMT powered RSS and real-time downhole
measurements with effective planning, to reap tangible benefits from drilling optimization.
With improved performance as a result of increased torque capacity and bit speed, and reduction of the stick-slip
mechanism, this new motor-driven rotary steerable technology has delivered superior performance and improved ROP in
challenging medium and hard formations. After more than 10,000 drilling hours and nearly half a million feet drilled, TMT
powered RSS technology is setting new records and exceeding benchmarks by bringing greater horsepower to the rock
destruction process with longer runs and higher ROPs.
Introduction
Optimized drilling systems include not only matched drilling tools, but also the integration of technology, processes, and
people across all stages of the drilling process1. This is important as the industry places emphasis on improvement to drilling
programs to reduce NPT, improve safety and efficiency, and optimize production.
Fit-for-purpose bottomhole assemblies (BHAs) together with a wide array of advanced downhole drilling tools have
greatly improved drilling efficiency and allowed much higher ROPs. Choosing the proper drilling system is critical to
boosting the well construction process and pushing the drilling limit. The proper BHA design and modeling is critical to
drilling the well and contributes to the optimization of drilling efficiency.
Delivering power downhole without increasing the rotary speed of the drillstring is a demand in some drilling
applications. Operators drilling extended-reach wells do not want to cause excessive wear on casing strings; additionally,
operators want a solution to mitigate stick-slip. TMT powered RSS is bringing these and other important benefits to the
drilling process.
Applications
TMT powered RSS has a broad range of applications, focused mainly on performance drilling and mitigating certain drilling
phenomena, such as vibration. Because of the wired connection and the modular design, drilling optimization or formation
evaluation sensors can be incorporated in front of the wired motor, providing great versatility to the BHA configuration.
From a performance point of view, TMT powered RSS increases ROP, decreases vibration, and decreases casing wear by
delivering the torque directly to the bit. The power section decouples the drilling string from the RSS, eliminating torsional
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vibration common in RSS applications. This benefit increases reliability not only for the RSS but also for all of the electronic
sensors in the string including optimization and formation evaluation sensors. In addition, the drill bit lasts longer and can
deliver better ROPs.
An important application for TMT powered RSS is in instances when the drilling rig experiences limit capacity related to
top drive power to rotate the drilling string or drillpipe torque limitations. Using a TMT powered RSS can reduce stress on
the rig and reduces wear on topdrive and drill pipe. Extended-reach drilling (ERD) and complex well profiles are classic
applications for TMT powered RSS by reducing surface torque and increasing reach capabilities.
A TMT powered RSS allows a variety of sensor combinations for multiple applications, including geosteering,
performance drilling, and reduced stick-out in casing while drilling applications.
Benefits
 More energy is directly applied to the bit, improving cutting efficiency and ROP while also overcoming stick-slip
and torsional related dysfunctions.
 Decoupling of the bit from the drillstring reduces transmission of vibrations to LWD and other BHA components,
improving life.
 Drill string rotary speed can be reduced to minimize casing wear while bit speed is optimized for the best drilling
performance.
 When applied in the proper drilling environment, TMT powered RSS improves ROP and reduces NPT, leveraging
to drill faster and with less risk, resulting in decreased costs.
 Improved ERD capabilities and exposure of the payzone, which can greatly reduce capital expenditure.
 The TMT powered RSS shows capability of significantly increasing ROP in conditions where rig topdrive does not
provide adequate torque and surface rev/min.
TMT Motor Design
RSS’s generally require communication with the measurement while drilling (MWD) system to transmit directional control
information to the surface and to transmit directional commands from the surface to the RSS. Directional information from
the RSS is critical information for the directional driller to help ensure the well path is being drilled according to the
directional plan. Communication between the RSS and MWD is also required to send formation evaluation information from
sensors located in the RSS to the surface. An example is the azimuthal gamma ray sensor located in the RSS. Wiring the RSS
motor allows transmission of power and high speed communications between the RSS and the MWD. The power section is
designed for high torque low speed operation. Fig. 1 shows a schematic of the main components of TMT.
The main challenges in the wired motor design include compensating for the eccentric motion of the rotor in the power
section, passing the transmission section and the bearing pack and compensating for different rotational speeds between the
rotor and upper housing.
Fig. 1—TMT main components.
TMT Motor Design Features
The rotor in a power section has an eccentric and axial motion that is a function of the lobe configuration, the fewer the lobes,
the higher degree of eccentric motion. When passing a conductor from the top of the rotor to the top of the motor housing,
this eccentric and axial motion must be compensated for. The method employed is to use a mechanical compensator that
compensates for movement in the axial and radial directions while providing a bidirectional continuous conductor for power
and communications transmission.
Rotation must also be compensated for because the rotor is decoupled from the upper housing in the rotational sense. A
slip ring is employed to allow for the differential rotation while, at the same time, providing a conductor for stable power
transmission and for high frequency, high speed communications.
The TMT motor design employs a titanium flex shaft to transmit rotation from the power section to the driveshaft. The
flex shaft design allows incorporation of a solid conductor through a bore in the center. In addition, the titanium flex shaft
provides high torque capability to drive higher loading below the wired motor.
The TMT motor has flexibility to use virtually any conventional power section provided the torque and rev/min
specification is within the tool limits and application requirements. The preferred power section type is uniform wall
thickness. The uniform wall thickness power section provides higher torque output and a higher temperature rating. Higher
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torque capability will allow for smoother rotation of the RSS and drill at a higher ROP. In addition, the uniform wall
thickness expands with temperature at a constant rate. Thinner rubber thickness that expands at a constant rate means that the
rotor and stator can be fit precisely for high temperature application. This allows application of the TMT technology at
temperatures up to 175°C.
Wired Motor— RSS BHA Design
The placement of a motor in an RSS assembly requires consideration of the impact on the MWD, RSS, and BHA
performance. The system described here is modular in design, which allows flexibility in placement of the motor in the BHA.
The motor can be placed between the RSS and MWD or within the modular MWD components.
The optimum placement of the power section is normally directly on top of the RSS and below the MWD. This placement
allows torque to be delivered directly to the RSS, allows higher bit speed without over-rotating the MWD, minimizes the
amount of string below the power section, and decouples vibration to the MWD and upper string.
The BHA can also be designed with drilling optimization sensors or LWD sensors located below the motor. Placement of
the drilling optimization sensor below the motor and above the RSS can be used to measure torque, weight on bit (WOB),
and bending on bit, for example, directly above the RSS for drilling optimization. LWD sensors can be placed directly above
the RSS and below the motor to obtain measurements closer to the bit.
The wired motor can also be configured with a bent housing for conventional motor applications, allowing power and
communication to the bottom of the motor and placement of sensors directly on top of the bit. Typical applications include
ranging sensors for intersection wells and LWD sensors for near bit formation evaluation. Fig. 2 shows some BHA
configurations depending on the application.
Fig. 2—Modular BHA configuration using a TMT powered RSS.
Case History 1—Offshore Deepwater UK
TMT powered RSS technology was used for an operator in a high-pressure/high-temperature (HP/HT) development well in
the UK Central North Sea. The challenge included maximizing ROP through hard chalk / limestone formations in the 12 1/4in. section and then drilling the 8-in. hole section through the HP/HT reservoir using LWD, eliminating the need for wireline.
In the 12-1/4in. section, the TMT RSS assembly was used to drill from 5,276 to 13,938 ft (1,608 to 4,248 m) measured
depth (MD). Average penetration rate was 78.6 ft/hr (24 m/hr), a 62% improvement over conventional rotary steerable
system performance in an offset well. Total footage drilled was 8,662 ft (2,640 m) with zero NPT.
In the 8 1/2-in. section, The HP/HT TMT RSS BHA with HP/HT LWD quad combo delivered the entire 2,323-ft (708-m)
section in a single run, intersecting all geological targets with zero NPT. In what was the fourth longest section in the UK for
drilling hours on bottom since records began, the LWD quad combo was downhole for 355 hr (14.8 days) with 296
circulating hr (12.3 days). Successful LWD performance eliminated the need for wireline logging, and the well reached total
depth (TD) at 16,232 ft (4,948 m) 25 days ahead of plan.
A major benefit of TMT technology is this case was decoupling the BHA to reduce vibration on the LWD and upper
string. This reduces damage and potential NPT while, at the same time, improving ROP and drilling performance. Fig. 3 (a
time based log) shows that, while some torsional resonance vibration exists below the motor, it is not transmitted to the LWD
tool and drillstring above.
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In this particular case, two downhole vibration sensors were part of the drill string, the first between the RSS and the
TMT motor and a second one behind the TMT motor within the LWD. The left graph in figure 3 is the data from the sensor
below the TMT, it shows in the track #4 high average values of vibrations both in Y and X axis; on the other hand, the right
graph in the same track (sensor above the TMT) shows minimum or null average vibration values both X and Y axis. This is
the decoupling effect from the TMT motor, which reduces transmission of vibrations.
The vibration measured below the TMT motor was -5.0 g average x-y delta torsional resonance. The vibration measured
above the TMT motor was -0.5 g average x-y delta torsional resonance, indicating a reduction due to the decoupling effect.
Fig. 3—TMT RSS application with vibration data above and below the motor.
Case History 2—Continental Europe Exploratory Campaign
In this vertical drilling application, the TMT powered RSS delivered maximum performance, outperforming the benchmark
well in the area with RSS or performance motors. During a four-well exploratory campaign, different drilling systems were
used aiming to maximize ROP. The structural setting in this continental Europe project corresponds to ancient Paleozoic and
Mesozoic depositions. Because of limited drilling, not much information was known at the beginning of the project.
Geological proposal, however, identified a hard/abrasive drilling environment, multilayered dipping, and folded
formations with dips in the range 40 to 70º. The stratigraphy of this area corresponds to the old Mesozoic and Paleozoic
geological eras starting with the Cretaceous period, subjacent by Jurassic, Devonian, Silurian, and Cambric. On top of the
hardness and abrasiveness, the geological cross-section shows important discontinuities with highly faulty events.
The first well was drilled with a rotary BHA including a straight mud motor. Low ROP was experienced, and the hole
inclination drifted until reaching an equilibrium angle around 20º. The drilling continued with the hole deviation moving in
the 10 to 20º range of inclination. The equilibrium angle is dependent on various factors, including formation dip angle,
drillability anisotropy, and drilling parameters in use. The well was TD with 13º of inclination and a vertical section of 270
m.
For the second well, a drilling motor was used with both sliding and rotating drilling modes in both intervals (12 1/4- and
8 1/2-in. hole sizes), ROP was lower compared to the first well because of the directional work to keep the well close to
vertical. The abrasiveness of the formation required performing several trips to drill each interval.
Another well used a push the bit vertical seeking tool powered with a motor above it; this approach managed to drill the
well vertical and improve ROP. Still, some drilling inefficiencies were experienced, including vibration that reduces the life
of the bit.
The last well incorporated a point the bit RSS together with a wired power section to drill both the 12 1/4- and 8 1/2-in.
intervals. The TMT powered RSS system not only managed to keep the well close to 0º inclination but, because of the
vertical cruise control mode in use, the drilling time was optimized by drilling the well in automatic vertical mode,
maximizing ROP. Fig. 4 (left) shows the time drilling curve for the four exploratory wells. The TMT powered RSS also
shows value to keep the well vertical. Fig. 4 (right) shows the deviation survey for the four wells.
During the entire run, the TMT powered RSS observed a strong build tendency caused by the steeply dipping formation.
The TMT powered RSS was operated with bit deflection over 60% and mainly at 80 to 90% to keep the wellbore vertical.
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Fig. 4—(left) drilling time curve for the four wells campaign; (right) inclination data for the four wells.
Vibration mitigation measures were employed at the direction of real-time engineering monitoring; however, low to
medium vibration severity was still present while drilling in the presence of interbedded formations; medium to high
vibration was also present when picking up the bit off bottom.
Case History 3—Middle East Hard Formation
A mature field application in Kuwait required TMT technology to improve ROP in a hard formation. The well consisted of
build and land sections in an 8 1/2-in. hole sizes, followed by a lateral section in 6 1/8-in. hole size. At the same time, a high
degree of steerability was required because of geologic uncertainty. TMT technology, along with high build rate RSS, was
chosen for this application.
In the 8 1/2-in. section, high build rate was required at landing because of formation tops coming in high. The required
trajectory was achieved with record ROP in this field, 60 ft/hr average, including connections and reaming times. A total of
2,500 ft was drilled building angle from 4 to 88° inclination in 32.5 drilling hours versus the 3.5 days planned for the section.
In the 6 1/8-in. lateral section, the assembly included a TMT powered RSS and LWD tools including geosteering service
to navigate through the reservoir. The assembly successfully drilled the reservoir for 1,500 ft, and then steered into the
secondary reservoir by dropping angle to 84° and steering inside that zone for approximately 900 ft. With an average ROP of
36.4 ft/hr in the 6 1/8-in. lateral section, this run also established a field record. Fig. 5 shows the trajectory created.
In the build section alone, a field record average ROP of 59.60 ft/hr saved the operator 2days, or approximately USD
100,000, while in the 6 1/8-in. section. The geosteering assembly achieved a field record average ROP of 36.4 ft/hr to save
the operator another 3 1/2 days, or about USD 175,000.
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Fig. 5—Realtime Geological Model Interpretation
Case History 4 Unconventional Play
Drilling efficiency requires attention to a variety of key indicators. Modeling BHAs together with advanced drilling
technologies contributes to the stability of the drilling system, optimum performance, and ultimately improvement to
efficiency. The fourth case history was in an unconventional play in which a TMT powered RSS was used to drill a long
lateral section, performing better than the best well previously drilled using mud motors.
The lateral hole intervals had been traditionally drilled with motors, achieving ROP of 50 to 70 ft/hr. Lately, however,
rotary steerable systems were introduced to drill long lateral complex trajectories, which has resulted in increased ROP. The
objective of this well was to use a TMT powered RSS to navigate in the best quality of rock while matching/exceeding the
established benchmark ROP as a minimum.
A TMT powered RSS assembly was used to drill the 8 1/2-in. lateral section of the well; total footage drilled with was
4,074ft MD in one run. Table 1 shows relevant data of the powered RSS application and presents run data, comparing a TMT
powered RSS to a motor.
TABLE 1—UNCONVENTIONAL LATERAL SECTION PERFORMANCE
Run Data
Powered RSS
Mud Motor
Start depth
6,673 ft MD
5,817 ft MD
End depth
10,747 ft MD
10,930 ft MD
Start inc/end inc
89.01°/86.97°
83.29°/87.65°
TVD range in the lateral
5,700 to 5,900 ft
5,700 to 5,900 ft
Motor used
6.75-in. TMT powered RSS
6.75-in. Motor
Bit used
FXG65D
FX64D
Avg flow rate
600 gal/min
600 gal/min
Below rotary hours
52 hr
138 hr
Drilling hours
15.6 hr
72 hr
Footage drilled in lateral
4,074 ft
4,879 ft
Effective ROP
261 ft/hr
68 ft/hr
The TMT powered RSS drilled in total 4,074 ft along the shale formation while geosteering and achieving good quality
rock based on formation evaluation data in real-time. The effective ROP was more than fourfold compared with the ROP
experienced in offset wells. The improvement of ROP by using the TMT powered RSS saved 24 hr of rig time. Fig. 6 shows
thecomparison of TMT powered RSS and best offset mud motor run.
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Fig. 6—Footage and ROP Comparison
The matched uniform wall thickness power section powering a point the bit RSS improved steerability and reduced
inefficiencies. Producing the power and speed as well as torque closer to the bit results in better steerability and a better
wellbore quality. This led to a record lateral in terms of ROP.
Drilling efficiency improved as vibration-related damage was reduced by minimizing stick-slip and by decoupling the
LWD tools from damaging shocks and torsional vibration. Some vibration was experienced with the TMT powered RSS,
mainly during circulation out of bottom. Fig. 7 shows a comparison of vibration experienced with both systems.
Fig. 7—Stick-slip vibration comparison (TMT powered RSS vs. downhole motor).
The TMT powered RSS has been a drilling efficiency step-change2. The proper planning in the right application can
deliver great benefits for the well construction. Fig. 8 shows 2013 footage and drilling time using TMT technology.
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Fig. 8—TMT Powered RSS cumulative footage and drilling hours.
Conclusions
 The TMT powered RSS with improved performance as a result of increased torque capacity and bit speed and
reduction of the stick-slip mechanism has delivered superior performance and improved ROP in challenging
medium and in hard formations.
 TMT wire technology is the most reliable way for a high speed and power communications between the RSS and
the MWD, allowing for BHA design flexibility to accommodate placement of downhole sensors ahead of the
power section.
 A benefit of the TMT powered RSS is that it decouples the BHA, reducing vibration on the LWD and upper
string. This reduces damage and potential NPT while, at the same time, improving ROP and drilling
performance.
 In a vertical drilling application, the TMT powered RSS has delivered maximum performance, outperforming
the benchmark well in the area in comparison to RSS alone or performance motors.
 The matched uniform wall thickness power section powering a point the bit RSS improves performance
significantly in hard formations and HP/HT applications.
Acknowledgements
The authors thank the management of Halliburton for their support of this project and encouragement to publish this work.
References
Alvord, C., Noel, B., Galiunas, L. et al. 2007. RSS Application From Onshore Extended-Reach-Development Wells Shows Higher
Offshore Potential. Paper OTC 18975-MS presented at the Offshore Technology Conference, Houston, Texas, USA. 30 April–3 May.
http://dx.doi.org/10.4043/18975-MS.
Zimmer, C., Pearson, J., Richter, D. et al. 2010. Drilling a Better Pair: New Technologies in SAGD Directional Drilling. Paper SPE/CSUG
137137 presented at the CSUG/SPE Canadian Unconventional Resources & International Petroleum Conference, Calgary, Alberta,
Canada, 19–21 October. http://dx.doi.org/10.2118/137137-MS.