AUTOMATED TECHNOLOGY FORoptimizing directional drilling with adownhole motor and measurementwhile drilling (MWD) system was devel-oped by assimilating surface torquewith downhole bit and drillpipe behav-ior.

The technology, devel-oped without introducingnew or additional equip-ment downhole, allowsdrillers to maximizedrilling efficiency andimprove wellbore qualitydue to less trajectory tor-tuosity during the slidingoperation of the drillingprocess.

The new technology inte-grates surface and MWDdata to provide the fol-lowing benefits in thesliding mode:

Improved ROP and hori-zontal reach capability;

Improved tool-face cor-rection while drilling,without coming off bottom;

• Improved well trajectory;

• Improved motor life due to lessstalling;

• Quick and accurate tool-face orienta-tion;

• No lost-in-hole exposure;

• Time savings when switching fromrotating to sliding without coming offbottom;

• Overall performance optimization;

• Less stress on the directional drillerdue to the automation of rocking andsliding techniques that were previouslyperformed manually.

The technology is owned by Noble Cor-poration. Slider LLC has the exclusiveworldwide commercial rights to marketthe technology, for which there are threepatents pending.

C O M M E R C I A L A P P L I C A T I O N

Slider technology was recently utilizedby a major operator on a barge rig in the

Gulf of Mexico with directional drillingcompany Integrated DirectionalResources (IDR). Scott Jones with IDRlearned about Slider LLC, contactedthem and was impressed enough withthe simplicity and potential time savings

that he in turn contacted the operator,suggesting that it be used in the devel-opment well being drilled with the bargerig.

“Everything worked as advertised,” MrJones said. “We’re pretty happy with it.

“I’ve been waiting for something likethis for a long time,” he added. “Proba-bly 75% of the wells being drilled withmud motors can see improved efficiencywith the Slider technology.”

Mr Jones also said that the robotics ofthe Slider technology is fairly straightforward. “What makes this technologywork or not work is that the logic thatdrives the robotics is well thought out.”

Mr Jones said he has already recom-mended it to other operators and hasseveral candidate wells.Slide Drilling

A motor and MWD system is designedwith a downhole motor and a bent hous-ing. The entire drillstring rotates to drilla tangent section, but only the bitrotates to produce a curve or bend.

Drilling with only the mud motor is com-

monly called slide drilling because thedrillpipe slides along the wellbore with-out rotating; the bent housing (and thus,the tool face) is oriented for trajectorycontrol.

With the motor and MWDsystem, sliding drilling effi-ciency is largely dependentupon the driller’s ability totransfer the proper amountof weight to the bit withoutstalling the motor, and toreduce longitudinal drag suf-ficiently to achieve and main-tain a desired tool-face angle.

Several techniques are avail-able for reducing longitudinaldrag. They include lubrica-tion, rollers, downhole vibra-tors within the bottom holeassembly (BHA), and the useof a “rocking” procedure thatconsists of turning the pipe tothe right and then to the leftby an amount that avoidsinterference with the toolface.

The effectiveness of eachtechnique varies with well conditionsbut each technique also has They. Limi-tations can include cost, rig downtime,permanent installation requirementsand increased risk for downhole failureor loss due to introduced equipment,vibrations and fishing restrictions.

By defining the relationships betweentorque, drag and downhole pipe move-ment, Slider LLC established the foun-dation for a control system for automat-ing the slide drilling process, helping toensure optimum performance.

B E N E F I T S O F T O R Q U E C O N T R O L

By sensing the amount of surface torqueneeded to transfer the proper amount ofweight to the bit, and eliminating theneed to come off bottom to make tool-face corrections, automated slidedrilling allows substantial increases inboth the daily footage drilled and thelength of horizontal departures that canbe achieved.

To commence slide drilling from therotary drilling mode, the driller simplyinitiates an automatic rocking action by

28 D R I L L I N G C O N T R A C T O R July/August 2004

Slider: new level of efficiency to directional drilling

Slider built a laboratory model to test the automation system that was comprisedof three basic components for simulating the surface controls, wellbore eventsand downhole conditions.

applying sufficient torque to the left andthen to the right to allow appropriateweight transfer to the bit.

The transfer of weight is controlledthrough the adjustment of rockingdepth, which is automatically adjustedto compensate for changes in reactivetorque.

Consequently, downhole back-offs due tosudden major motor stalls are avoided,and no time is lost in orienting the toolface.

Corrections in tool-face angle are easilyachieved through additional torquepulses (bumping) during the rockingcycles.

T H E O R Y O F T O R Q U E C O N T R O L

To understand the effect of surfacetorque and reactive torque on longitudi-nal drag, a velocity vector was derivedfrom the combination of pipe rotation tothe right and left, and drillpipe move-ment forward during drilling.

The velocity component is a function ofthe position of the pipe along the entirewellbore. The direction and magnitudeof this vector will dictate the degree ofreduction in longitudinal drag.

Left-and-right torque rocking initiatedby the top drive reduces longitudinaldrag in the wellbore, allowing thedrillpipe to rotate from the surface downto a point where torque from rotationalfriction against the side of the hole stopsthe drillpipe from turning.

Meanwhile, reactive torque generatedby the drill motor is transmitted up thepipe to a point where it is overcome bythe bottom hole friction along theBHA/drillpipe system, referred to as thepoint of interference.

Between this point and the bit(described here as the zone of interfer-ence), the velocity component again dic-tates the degree of reduction in longitu-dinal drag and the change in tool-faceorientation.

To prevent pipe rotation from the sur-face from penetrating the zone of inter-ference, the system is tuned based uponon-bottom and off-bottom torque meas-urements in the field during each job.

The point of interference changes as thereactive torque changes. To keep the dif-ference between the depth of the point ofinterference and the depth of rockingrelatively constant, thus providing aknown constant actual sliding distance,an automated control system must com-pensate for this change.

The actual sliding distance is the lengthof drillpipe that does not turn during therocking cycle.

Ideally, an actual sliding distance of zerowould appear to provide the fastestweight transfer to the bit.

However, eliminating the actual slidingdistance is not only impossible toachieve without affecting the tool face, itis also not necessary to provide goodcontrol of pipe movement, as proven in

July/August 2004 D R I L L I N G C O N T R A C T O R 29

laboratory and field experiments.

C O M P O N E N T S A N D O P E R A T I O N

Input parameters to the control systeminclude surface torque, standpipe pres-sure and/or downhole tool-face angle.The automation technology packagecomprises a software and a hardwarecomponent.

Software. The software component col-lects torque and standpipe pressuredata required to determine the need foradjustments during drilling.

Standpipe pressure provides an indica-tion of reactive torque, which changescontinually. In monitoring reactivetorque via standpipe pressure, the sys-tem continuously adjusts the rockingdepth (amount of surface torque appliedto the right and left) to compensate forthe effect of reactive torque.

Because factors unrelated toreactive torque such as cut-tings buildup, partiallyplugged nozzles, etc. canaffect changes in the stand-pipe pressure.

The downhole tool-face meas-urement is used to determinethe amount of correctionneeded to restore the toolface to a predetermined tar-get angle.

To correct the tool-face angleduring a rocking cycle, thedriller can “roll” or “bump”the tool face by initiatingtorque pulses. These correc-tions can be made to the rightor left with ease.

Hardware. The hardwarecomponent features a univer-sal robotics solution to fit anytop drive. It is non-intrusiveand requires no rig modifica-tions for operation.

The robot actuates the control systems(e.g. buttons, switches, wheels, etc) asdirected by the software.

Safety. Though the automated system’srobotics eliminates the need for mostmanual adjustments required in conven-tional slide drilling, the system isdesigned to allow manual interventionat any time, assuring the highest level ofoperational safety.

Complete redundancy was built into thetorque control system to avoid left-handtorque overshoot and potential back-off,including a software check in the controllogic and a hardware system thatassigns an operator-adjustable torquelimit to the top drive.

The automated control system can beinstalled in less than 2 hours withoutinterrupting the drilling process.

Installation of sensors and the panelcontrol box is the primary task involved.

D E V E L O P M E N T M E T H O D O L O G Y

To maximize the potential for successfulfield tests, Slider LLC conceived a strat-egy comprising three basic steps:

• Build a laboratory physical simulator;

• Conduct field tests with a smaller hor-izontal well drilling rig equipped with a

hydraulic power swivel to validate theprototype’s reliability and ease of instal-lation and operation;

• Scale-up production to a universalproduct line.

The laboratory physical simulator usedto test the automation system com-prised three basic components for simu-lating surface controls, wellbore eventsand downhole conditions.

The surface system contained thedriller’s console, drawworks, top drive,and instrumentation package.

The wellbore system included a special-ly designed pipe for simulating the samewraps that drillpipe would be subject toin the field (d-less analysis was used)and a borehole torque and drag produc-ing device.

The bottomhole system included adownhole motor with rock/bit interac-tion and adjustable formation strengthcapabilities. The rock/bit device wasused to generate reactive torque, and itsoutput could be varied based on theaggressiveness of the bit being simulat-ed.

The formation strength device allowedfor axial advancement of the bit whiledrilling to simulate softer or harderrock.

After initial manu-facturing of thephysical simulator,the system and itsvarious compo-nents were cali-brated againstfield rig data.

The same rig fromwhich this datawas gathered waslater used for field-testing the auto-mated system.

This assured thehighest possibledegree of accuracyduring laboratoryexperiments andminimized the fieldtrial duration.

The control systemwas developed forthe laboratory sim-ulator in such a

way that the same software could beused in the laboratory and in the field.

Because the first field test was sched-uled for a rig with a hydraulic powerswivel, an industrial control panel forthat system was modified so that thecontrol panels could be swapped on therig during the field test.

After the second field test, this adapta-tion was no longer necessary because

30 D R I L L I N G C O N T R A C T O R July/August 2004

Input parameters to the control system include surface torque, standpipe pressure and/ordownhole tool-face angle. The automation technology package comprises a software anda hardware component.

robots (servo motors with appropriatesoftware and hook-up capabilities) hadbeen added to provide a universal solu-tion for all types of top drives.

Component Testing. All componentsperformed according to plan in the ini-tial field test. The concepts learned inthe laboratory were proven and all thediscoveries were confirmed.

After five days of testing without anydowntime, developers decided that itwas safe to move from alpha testing tobeta testing and remain on location,drilling the well up to the end of thelease boundary.

This was a rather unique and fortunateopportunity, considering that numerousfield trials are normally required toprove new technology, even after thor-ough laboratory testing.

F I E L D T E S T R E S U L T S

On the first job, the average daily slidingROP increased from 5-7 ft per hour to arange of 10-20 ft per hour. The ROP inthe rotary drilling mode with the down-hole motor was 40 ft per hr.

On the second job, the average dailysliding ROP increased from 3-4 ft perhour to a range of 5.6-7.2 ft per hour.Again, the ROP in the rotary drillingmode with the downhole motor was 40ft/hr.

The field test well had a 4,000 ft+ hori-zontal departure and the directionaldriller experienced great difficulty inmanually locking in the tool face to thedesired value.

After a 45 minute attempt, the automat-ic torque control system was deployed.The tool face was easily obtained andmaintained at the desired range of 140°-165°.

Thirty minutes after the automatictorque control system was put into use,the downhole motor stalled and thedriller attempted to correct the tool facemanually.

After five minutes without success, theautomatic torque control system wasagain deployed and successfully cor-rected the tool face.

Extended Reach. When a motor andMWD system is used to drill a direction-al well, the sliding controls the wellbore

trajectory. An inability to obtain thedesired tool face or to achieve the rate ofpenetration necessary for sliding oftenresults in increased drilling time andcan be tolerated only for a short while.

The inability to slide can cause the tar-get envelope to be missed or the lateralsection to be cut short.

In one job, the driller encountered diffi-culty in trying to orient and control thetool face manually at higher step-outs.As a result, drilling economics limitedthe length of this lateral section.

This difficulty was not experienced withthe automatic torque control system,although more data are necessary fordetermining limits of extended reachdrilling.

Improving Motor Life. Stalling ofdownhole motors due to longitudinaldrag and sudden transfers of weight tobit are known to cause premature motorfailure due to excessive stresses exertedon the rubber component by the fluidblow-by.

During the first 45 minutes that tool-face orientation was attempted manual-ly, the downhole motor stalled ninetimes.

Only one stall was observed during theuse of the automatic torque control sys-tem.

Bumping. A “bumping” procedure isused to achieve a small tool-face correc-tion (typically 10° to 40°). Such correc-tions are made after torque is increasedduring a rocking cycle.

If a right-hand correction is required,the right-hand torque will be increasedby an amount determined by the direc-tional driller.

A similar procedure is used for a left-hand tool-face correction.

This procedure is very simple and iscommonly used with the automatedtorque control system to orient the toolface from its random landing position asthe driller transitions from the rotarymode to the sliding mode.

This technique can also be used to cor-rect the tool face if it begins to roll awayfrom the target value while sliding.

Rolling. The automatic torque controlsystem provides additional steering

capabilities to a motor and MWD systemthrough a procedure called rolling inwhich a continuous small torque bias isapplied to the left or right to slowly buildor drop the angle of trajectory.

The tool face is rolled to the right whenthe right-hand torque is increased andthe left-hand torque remains constant.

Likewise, the tool face is rolled to theleft when the left hand torque isincreased while the left-hand torqueremains constant.

At the end of a slide run, the directionaldriller decided to reduce the inclinationby bringing the tool face closer to thelow side.

This was accomplished by increasingthe depth of the right-hand torque whileholding the left-hand torque value con-stant.

A smooth roll of the tool face towardsthe right was observed over a 20-minuteperiod and the tool-face angle changedfrom 155° to 200°. n

July/August 2004 D R I L L I N G C O N T R A C T O R 31