+ All Categories
Home > Documents > turns for rotary steerable drilling

turns for rotary steerable drilling

Date post: 14-Dec-2015
Upload: riezaf
View: 57 times
Download: 3 times
Share this document with a friend
rotary steerable drilling technology has evolved considerably, as it hass unique capabilities
Popular Tags:
4 Oilfield Review Better Turns for Rotary Steerable Drilling Mike Williams Sugar Land, Texas, USA For help in preparation of this article, thanks to Glaucio Alves Barbosa, Chris Lenamond, Roger Pinard and Ulisses Sperandio, Macaé, Brazil; Emma Bloor, Liz Hutton and Curtis Robinson, Sugar Land, Texas, USA; Tim Curington and Paul Wilkie, Stonehouse, England; Bjørn Engedal, Norsk Hydro, Stavanger, Norway; Ricardo Juiniti Bernardo, Petrobras, Macaé, Brazil; Hilaire Tchetnga, Luanda, Angola; and Paul Wand, London, England. adnVISION (Azimuthal Density Neutron), PERFORM (Perfor- mance Through Risk Management Process), PowerDrive, PowerDrive Xceed, PowerDrive Xtra and PowerPulse are marks of Schlumberger. Rotary steerable drilling technology has evolved considerably since its dramatic entry to the field in the late 1990s. The unique capabilities of the newest systems offer increased flexibility and greater reliability for drilling complicated wellbore trajectories in harsh environments. Rotary steerable systems arrived on the drilling scene in the late 1990s to immediate acclaim. An extended-reach well drilled during 1997 in the Wytch Farm field in the UK was the first well with a departure more than 10 km [6.2 miles] drilled using this new technology. 1 Up until that well was drilled, engineers approximated the operation of rotary steerable systems by using > Evolution of directional-drilling technology. Positive-displacement motors and steerable drilling motors supplanted primitive bit deflection using whipstocks. Rotary steerable systems, introduced in the late 1990s, were the first devices to provide three-dimensional trajectory adjustment while rotating continuously. Bit deflection using whipstocks Limited control Missed targets Positive-displacement motor Improved directional control Inefficient Steerable drilling motor Rotary and sliding modes controlled at surface Improved directional control Tortuosity from slide drilling limits reach Rotary steerable system Continuous rotation Excellent directional control Improved borehole quality Increased rate of penetration Highly efficient
Page 1: turns for rotary steerable drilling

4 Oilfield Review

Better Turns for Rotary Steerable Drilling

Mike WilliamsSugar Land, Texas, USA

For help in preparation of this article, thanks to GlaucioAlves Barbosa, Chris Lenamond, Roger Pinard and UlissesSperandio, Macaé, Brazil; Emma Bloor, Liz Hutton and CurtisRobinson, Sugar Land, Texas, USA; Tim Curington and PaulWilkie, Stonehouse, England; Bjørn Engedal, Norsk Hydro,Stavanger, Norway; Ricardo Juiniti Bernardo, Petrobras,Macaé, Brazil; Hilaire Tchetnga, Luanda, Angola; and PaulWand, London, England.adnVISION (Azimuthal Density Neutron), PERFORM (Perfor-mance Through Risk Management Process), PowerDrive,PowerDrive Xceed, PowerDrive Xtra and PowerPulse aremarks of Schlumberger.

Rotary steerable drilling technology has evolved considerably since its dramatic

entry to the field in the late 1990s. The unique capabilities of the newest systems

offer increased flexibility and greater reliability for drilling complicated wellbore

trajectories in harsh environments.

Rotary steerable systems arrived on the drillingscene in the late 1990s to immediate acclaim.An extended-reach well drilled during 1997 inthe Wytch Farm field in the UK was the first well

with a departure more than 10 km [6.2 miles]drilled using this new technology.1 Up until thatwell was drilled, engineers approximated theoperation of rotary steerable systems by using

> Evolution of directional-drilling technology. Positive-displacement motors and steerable drillingmotors supplanted primitive bit deflection using whipstocks. Rotary steerable systems, introduced in the late 1990s, were the first devices to provide three-dimensional trajectory adjustment whilerotating continuously.

Bit deflection using whipstocks• Limited control• Missed targets

Positive-displacement motor• Improved directional control• Inefficient

Steerable drilling motor• Rotary and sliding modes controlled

at surface• Improved directional control• Tortuosity from slide drilling

limits reach

Rotary steerable system• Continuous rotation• Excellent directional control• Improved borehole quality• Increased rate of penetration• Highly efficient

Page 2: turns for rotary steerable drilling

Spring 2004 5

steerable motors in the rotary drilling mode asmuch as possible. Drillers clearly saw the potential for a continuously rotating directional-drilling tool to eliminate slide drilling, improvehole cleaning, increase penetration rate andreduce the risk of differential sticking, among ahost of other benefits.2

Today, drillers realize these and many otherbenefits with a new generation of rotary steer-able systems that garner fewer headlines butoffer substantial improvements over previoustechnology. For example, it is now possible touse a bicenter bit to enlarge boreholes whiledrilling with a rotary steerable system, saving rigtime consumed by separate drilling and reamingoperations.3 State-of-the-art rotary steerable systems have minimal interaction with the bore-hole. They use tool internal rather than externalmeans to reference their position and attitudewithin the borehole and thereby preserve bore-hole quality. Indeed, the most advanced systemssimply exert consistent side force similar to traditional stabilizers that rotate with the drillstring or orient the bit in the desireddirection while continuously rotating at thesame number of rotations per minute as thedrillstring. This latter approach uniquely provides dogleg severity of over 8°/30 m [8°/100 ft]in the softest of formations in which constantborehole interaction is impossible.4

Advanced rotary steerable systems must con-tend with more than complicated trajectories.These systems are now built to perform in thetoughest environments, taking advantage ofenclosed components that protect the tool inwellbore temperatures to 302°F [150°C], highlyabrasive formations, all types of fluids and high-

shock environments. These advances in hardwareare coupled with durable, proven electronics thatimprove reliability and reduce risk.

Oilfield Review presented early achieve-ments in specialized rotary steerable drillingoperations several years ago.5 In this article, webriefly review directional-drilling technology andthen focus on recent successes in Brazil andNorway involving novel applications of the mostadvanced rotary steerable systems.

Drilling in New DirectionsDirectional drilling began in the early 1970s as atechnique to reach otherwise inaccessiblereserves, particularly those drilled from offshorewell templates (previous page). The earliestdirectional-drilling technology involved devicessuch as whipstocks that deflected the drill bit, amethod that offered limited control and that alltoo frequently resulted in missed targets.6 Theintroduction of the positive-displacement motoroffered steering capability and with it, direc-tional control, but the motor lacked theefficiency drillers sought. Eventually, steerablemotors allowed rotation and sliding of the drill-string from surface, which further improveddirectional control. Nevertheless, this technologyremained inefficient and risky because theextreme torque and drag limited drilling capabil-ity in sliding and rotating modes, leaving sometargets inaccessible. In addition, the wellboretortuosity the steerable motors produced in thesliding mode was unacceptable, in part becausetortuosity makes future sliding more difficult andbecause tortuosity can impede critical operationsfor formation evaluation and running casing; logquality also suffers in rough holes.

The introduction of rotary steerable technol-ogy eliminated several disadvantages of previousdirectional-drilling methods. Because a rotarysteerable system drills directionally with contin-uous rotation from the surface, there is no needto slide the tool, unlike drilling with a steerablemotor. Continuous rotation transfers weight tothe bit more efficiently, which increases the rateof penetration (ROP). Rotation also improveshole cleaning by agitating drilling fluid and cut-tings, allowing them to flow out of the holerather than accumulating as a cuttings bed.Advanced rotary steerable systems are designedto improve fluid circulation and cuttingsremoval. Efficient cuttings removal reduces thechance for the bottomhole assembly (BHA) tobecome stuck or pack off.7

Continuous rotation and better hole cleaningreduce the chance of mechanical and differen-tial sticking of the drillstring. No stationarycomponents contact the casing or borehole. Inaddition, rotary steerable technology improvesdirectional control in three dimensions. The net result is a smoother, cleaner and longer well-bore, drilled faster with fewer stuck-pipe andhole-cleaning problems (below). The higher

1. For more on Wytch Farm drilling: Modi S, Mason CJ,Tooms PJ and Conran G: “Meeting the 10 km DrillingChallenge,” paper SPE 38583, presented at the SPEAnnual Technical Conference and Exhibition, San Antonio,Texas, USA, October 5–8, 1997.Allen F, Tooms P, Conran G, Lesso B and Van de Slijke P:“Extended-Reach Drilling: Breaking the 10-km Barrier,”Oilfield Review 9, no. 4 (Winter 1997): 32–47.

2. Slide drilling refers to drilling with a mud motor rotatingthe bit downhole without rotating the drillstring from thesurface. This directional-drilling operation is conductedwhen the bottomhole assembly has been fitted with abent sub or a bent housing mud motor, or both. Withoutturning the drillstring, the bit is rotated with a mud motor,and drills in the direction it points. The wellbore trajectorycan be controlled by limiting the amount of hole drilled inthe sliding versus the rotating mode.

3. A bicenter bit is an integral bit and eccentric reamerused to simultaneously drill and underream, or enlarge,the hole. For more on drill bits: Besson A, Burr B,Dillard S, Drake E, Ivie B, Ivie C, Smith R and Watson G:“On the Cutting Edge,” Oilfield Review 12, no. 3(Autumn 2000): 36–57.

4. The build angle is also referred to as dogleg severity. Adogleg is an abrupt turn, bend or change of direction in a wellbore, and can be quantified in degrees or degreesper unit of distance.

> Comparison of hole quality using a mud motorand the PowerDrive Xceed rotary steerablesystem. The mud motor tends to produce anuneven, overgauge or spiral borehole (top). ThePowerDrive Xceed borehole (bottom) is smoothand in gauge.

Hole “spiraling”

5. Downton G, Hendricks A, Klausen TS and Pafitis D:“New Directions in Rotary Steerable Drilling,” OilfieldReview 12, no. 1 (Spring 2000): 18–29.

6. A whipstock is an inclined wedge placed in a wellbore toforce the drill bit to start drilling in a direction away fromthe wellbore axis. The whipstock must have hard steelsurfaces so that the bit will preferentially drill througheither casing or rock rather than the whipstock itself.Whipstocks may be oriented in a particular direction ifneeded, or placed into a wellbore blind, with no regard tothe direction they face. Most whipstocks are set on thebottom of the hole or on top of a high-strength cementplug, but some are set in the open hole. Use of a whip-stock presents some risk of mechanical sticking in acasing shoe or milled window.

7. Packing off refers to plugging of the wellbore around adrillstring. This can happen for a variety of reasons, themost common being that either the drilling fluid is notproperly transporting cuttings and cavings out of theannulus, or portions of the wellbore wall collapse aroundthe drillstring. When the well packs off, there is a suddenreduction or loss of the ability to circulate, and high pumppressures follow. If prompt remedial action is not suc-cessful, an expensive episode of stuck pipe can result.

Page 3: turns for rotary steerable drilling

quality of the resulting wellbore makes formationevaluation and running casing less complicated,and reduces the risk of getting stuck.

This vast assortment of advantages has maderotary steerable systems an essential part ofmany drilling programs. Exploration and produc-tion (E&P) companies routinely designchallenging well trajectories to intersect distantor multiple targets and to maximize oil and gasproduction. Other common challengesaddressed by rotary steerable drilling includecompartmentalized reservoirs, deepwater

reservoirs, environmentally constrained develop-ments, distant platforms or drilling pads, andeven certain marginal fields in which economicsuccess depends on accurate placement of ahigh-quality borehole.8 During operations, robustlogging-while-drilling (LWD) technology canhelp companies refine trajectories to takeadvantage of the well-placement capabilities ofrotary steerable systems.9 Successful drillingrequires downhole tools that withstand high-shock environments, high temperatures andabrasive rocks, often while building angle anddrilling extended-reach boreholes.

Drilling the Extra Mile in Soft FormationsThe efficiency and reliability of PowerDriverotary steerable systems optimize directionaldrilling in a variety of hole sizes. A key aspect of PowerDrive technology, including the PowerDrive Xtra tool, is continuous rotation ofthe entire steering system at the same speed asthe bit (left). The tool’s immediate response tocommands from surface improves steeringtowards a specific target. Near-bit inclinationand azimuth measurements apprise the drillerof the effectiveness of the steering commands,further improving directional control. Finally,like other PowerDrive systems, the PowerDriveXtra device handles a variety of drilling chal-lenges, from using its directional control to drillprecisely vertical wells to kicking off and drillingextended-reach tangent sections.

The attributes of the PowerDrive Xtra toolbecame especially significant when drilling long,nearly horizontal wellbores in deep water off-shore Brazil. In this region, drilling relativelysimple well profiles is difficult because the for-mations tend to be soft shales and marls.Drilling rig costs are high. The introduction ofPowerDrive technology for deepwater develop-ment wells in Brazil has trimmed an average oftwo rig days per 121⁄4-in. hole section and one rigday per 81⁄2-in. hole section. In 95 tool runs in Brazil, no PowerDrive tools have been lost in the hole.

In the Voador field, Petrobras drilled a pilothole to establish reservoir boundaries and asidetrack hole to optimize heavy-oil productionfrom the well (next page). The PowerDrive Xtratool drilled the 84° inclination of the 7-VD-10HP-RJS sidetrack hole with maximum build angle of6.5°/30 m [6.5°/100 ft] into the target formationas planned, with instantaneous rates of penetra-tion (ROPs) as high as 75 m/hr [248 ft/hr]. Theaverage ROP using PowerDrive Xtra technologywas 35 to 40 m/hr [115 to 131 ft/hr], which wastwice that of a steerable motor in offset wells.Moreover, the rotary steerable system could sus-tain longer bit runs and better directionalcontrol than a motor because the friction of themotor limits ROP. As friction builds whendrilling with a motor, there is a decrease indirectional control.

This type of drilling success in a soft forma-tion requires more than downhole tools. In thiscase, using the PERFORM Performance ThroughRisk Management Process, the wellsite engi-neers closely monitored drilling parameters,cuttings morphology, real-time torque and drag,and equivalent circulating density to ensuregood hole cleaning and to detect wellbore-stability problems.10

6 Oilfield Review

> PowerDrive Xtra rotary steerable system. Thecontrol unit contains electronics and sensorsand controls the trajectory. The bias unit appliesforce to the bit. Several PowerDrive Xtra systemsare available for drilling 53⁄4- to 181⁄4-in. holes.

Control unit

Bias unit

Page 4: turns for rotary steerable drilling

Spring 2004 7

LWD images acquired during the trip out ofthe hole were downloaded at surface. Whencompared with images acquired at differenttimes, for example, during drilling, these time-lapse images confirmed wellbore-stabilityproblems in the shales, which were first indi-cated by the cuttings morphology and increasingdrag. In this well, the PERFORM process helpedengineers determine that the mud weight wastoo low and that hole cleaning was suboptimal.The well was drilled successfully to total depthby managing both parameters while drilling.

Petrobras took PowerDrive Xtra technologyin a different direction when the company

planned a vertical, deepwater exploration well,1-RJS-600, near a salt dome. The companywanted to drill close to the salt dome, where for-mation dip was greater than 20°, but alsowanted the well to penetrate the reservoir verti-cally. Keeping the borehole perfectly vertical,rather than deviating and correcting back to vertical, would produce a smoother wellbore. Asmoother wellbore facilitates running larger casing, and offers the possibility of using anextra string of casing at some later stage in the operation. Although a vertical drilling tool couldhave done the job, Petrobras wanted to use aPowerDrive Xtra system to ensure that the drill-string would rotate throughout drilling

operations while allowing application of themaximum weight on bit to maintain the highestpossible penetration rates.

> Voador field, Campos basin, offshore Brazil (bottom right). Petrobras used the PowerDrive Xtrasystem to drill a pilot hole to establish reservoir boundaries, and a sidetrack hole to optimize heavy-oilproduction (bottom left). The tool drilled the 84° inclination of the sidetrack hole with maximum buildangle of 6.5°/30 m [6.5°/100 ft] into the target formation as planned (top), with an average rate ofpenetration (ROP) of 35 to 40 m/hr [115 to 131 ft/hr], which was double that of the steerable motordeployed in offset wells.


Voador field












01,700 1,900 2,100 2,300

Depth, m





n or






le, °

2,500 2,700 2,900










ROP Inclination Azimuth Build angle

13 3⁄8-in. casing at 1,692 mmeasured depth (MD)

9 5⁄8-in. casing at 2,885 m MD

Total depth 3,336 m MD

Plan Actual

8. For an example of rotary steerable drilling in a marginalfield: Musa MB, Wai FK and Kheng LL: “Fit-for-PurposeTechnologies Applications in Commercialising aMarginal Oil Field,” paper SPE 80462, presented at theSPE Asia Pacific Oil and Gas Conference and Exhibition,Jakarta, Indonesia, April 15–17, 2003.

9. For an example of the roles of LWD and rotary steerablesystems in well placement: Tribe IR, Burns L, Howell PDand Dickson R: “Precise Well Placement With RotarySteerable Systems and Logging-While-Drilling Measurements,” SPE Drilling & Completion 18, no. 1(March 2003): 42–49.

10. For more on the PERFORM process: Aldred W, Plumb D,Bradford I, Cook J, Gholkar V, Cousins L, Minton R,Fuller J, Goraya S and Tucker D: “Managing DrillingRisk,” Oilfield Review 11, no. 2 (Summer 1999): 2–19.

Page 5: turns for rotary steerable drilling

The PowerDrive Xtra system reduced thehole inclination from 0.47° to 0.03° at the begin-ning of the first run and maintained an overallinclination of 0.15° over the course of two runsof the tool. The well was drilled 2.5 days aheadof the schedule specified in the authorization forexpenditure (AFE), saving US$ 750,000. Workingtogether, Petrobras and Schlumberger used thePowerDrive Xtra tool to drill the well accordingto technical specifications and ahead of plan,which improved the financial impact of thisendeavor. In light of these results, Petrobrasplans to deploy PowerDrive Xtra technology in atleast 40% of the more than 100 offshore wellsslated for drilling during 2004.

Openhole Sidetracking in Complicated FormationsTool reliability, steerability and durability arekey factors when drilling complicated well tra-jectories in harsh drilling environments. Rotarysteerable systems are a natural fit for theseoperations because full rotation of the systemslessens the likelihood of operational mishaps,such as mechanical sticking.

The reliability and durability of the PowerDrive Xceed rotary steerable system forharsh, rugged environments make it suitable fordrilling the most difficult wells (right). The sys-tem incorporates electronics from the proven,durable PowerPulse measurements-while-drilling(MWD) telemetry system, which can operatemore than 1,000 hours without failure.

Steerability of the PowerDrive Xceed systemis regulated by an internal steering mechanismand through traditional three-point contact withthe borehole wall. The internal steering mecha-nism is completely enclosed to provide a greaterdegree of accuracy than a tool with an externalsteering mechanism because the internal steer-ing mechanism limits interaction between thetool and the hole. Only rotating elements contact the borehole, so directional drilling iscontrolled by the tool instead of the shape of the

hole. This independence of the rotary steerablesystem from the borehole facilitates complicateddrilling applications, drilling with bicenter bitsand drilling openhole sidetracks with great reli-ability, even at high build rates. In addition, thelimited contact between the tool and the bore-hole improves hole quality and maximizes ROP.

The PowerDrive Xceed system is designedspecifically for tough environments. Enclosedcomponents and stationary internal seals protectthe tool in wellbore temperatures to 302°F, highlyabrasive formations, all types of fluids, and high-shock environments. Its minimal contact with theborehole wall makes the tool less susceptible towear in abrasive formations. In addition, the toolcan build angle up to 8°/100 ft [8°/30 m], whichallows it to drill demanding trajectories.

Many of these advantages of the rotary steer-able system were tested in the Njord field, in theNorwegian sector of the North Sea (next page).11

Numerous faults separate the reservoir intocompartments that must be tapped individually,but determining the location and extent of thecompartments is a difficult task. Some of therocks are extremely abrasive, while others areprone to instability.

Njord operator Hydro used the PowerDriveXceed system to perform an openhole sidetrackin the A-10 BY3H well. The system successfullydrilled the sidetrack from open hole at 91° incli-nation. The plan called for a drop in inclinationfrom 91° to 88.5°, while turning from an azimuthof 179° to 170°. The section was drilled fromopenhole sidetrack to total depth in one run, afeat never previously achieved in this field. Thissaved approximately two days of rig time.

The PowerPulse system measured downholevibrations, which were lower in quantity anddegree than comparable runs, indicatingimproved drilling efficiency. Performing morethan 90% of the tool settings while drilling withthe tool on bottom also enhanced efficiency byreducing nonproductive time.

8 Oilfield Review

11. Rotary steerable systems have been used in the Njordfield to drill extremely complicated wells, including a W-shaped well. For more information: Downton et al,reference 5.For more on the Njord field:http://www.hydro.com/en/our_business/oil_energy/production/oil_gas_norway/njord.html (viewed January 12, 2004).

12. von Flatern R: “Rotary Steerables Ready for the Mainstream,” Offshore Engineer 28, no. 4 (April 2003):32–34, 36.

13. For more on slimhole systems: Kuyken C, van der Plas K,Frederiks K, Williams M and Cockburn C: “Developingand Using Slimhole Rotary Steerable Systems in theNorth Sea Changing the Economics of Mature AssetDrilling,” paper SPE 83948, presented at the SPE Offshore Europe 2003 Meeting, Aberdeen, Scotland,September 2–5, 2003.

> PowerDrive Xceed rotary steerable system.The power-generation module supplies powerfor steering and control. The control unit containselectronics and sensors that take measurementsto control the steering assembly. The steeringsection continuously orients the tilted bit shaft tocontrol the drilling direction and build angle.

Power-generation module: turbine-driven alternator supplies power for steering and control.

Control system: electronics and sensor package take measurements to control steering assembly.

Steering section: assemblycontinuously orients thetilted bit shaft to control the drilling direction andthe dogleg severity of the borehole.

Page 6: turns for rotary steerable drilling

Spring 2004 9

Engineers used real-time adnVISIONAzimuthal Density Neutron images to improvesteering and penetrate three times more pro-ducible reservoir than any previous well in thisfield. Using continuous inclination measurements4 m [13 ft] behind the bit, the directional drillerwas better able to respond to the changes in thewell plan requested by the wellsite geologist.

Drilling with a TwistE&P companies plan increasingly exotic well-bore trajectories and configurations that pushthe limits of existing directional-drilling technol-ogy, while simultaneously seeking cost savingsand improved quality in these operations. Thesuccess of the first-generation rotary steerablesystems increased demand substantially; forSchlumberger, this has led to the use of rotarysteerable systems in 26% of the footage Schlumberger tools drilled during 2003. Most ofthis drilling occurs in offshore environments, but the technology is also applicable in onshore operations. Industry observers believe that itswidespread, rapid acceptance and applicationnow make rotary steerable drilling a main-stream technology.12

Slimhole rotary steerable systems, such asthe PowerDrive Xtra 475 tool, have demonstratedoperational and economic merit, particularly inmature fields, where the production-rate limitations of slim holes are not an issue.13 Liketheir full-sized counterparts, these slimhole toolsprovide the mechanical advantages of continuousrotation, but also offer the economic rewards ofusing less drilling fluid, cement and other mate-rials. Slimhole drilling also minimizes cuttingsand cuttings-disposal costs because of thesmaller hole volume. Slimhole rotary steerabledrilling is expected to play a vital role as morefields reach maturity because this technologyimproves efficiency and lowers cost.

In the future, rotary steerable technologymust address operator expectations for evenfaster rates of penetration. Powered rotarysteerable tools will make this possible. Otherenhancements will provide even greater reliability and efficiency. Ultimately, “shoe toshoe” rotary steerable drilling will allow compa-nies to drill out the casing shoe and continuedrilling to the next casing point in a single run.With industry costs for nonproductive drillingtime estimated at US$ 5 billion per year, rotary steerable systems will be a key to preventing orreducing these significant losses.—GMG

> Njord field location, offshore Norway.


0 200 400 miles

200 400 600 km

Njord field



Norwegian Sea