spe-13349 managing drilling vibration through bha design optimizationiptc-13349-ms

8/10/2019 SPE-13349 Managing Drilling Vibration Through BHA Design OptimizationIPTC-13349-MS

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Copyright 2009, International Petroleum Technology Conference

This paper was prepared for presentation at the International Petroleum Technology Conference held in Doha, Qatar, 79 December 2009.

This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarilyreflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor SocietyCommittees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum TechnologyConference 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 conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, IPTC, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax +1-972-952-9435.

AbstractSignificant performance improvement has been achieved by successfully managing drilling vibrations through bottomhole

assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Prior literature has

described improvements in operating practices to manage vibrations(1,2)as a key component of this ROP (rate of penetration)

management process. In a parallel work activity, the redesign efforts have provided additional performance improvements ofapproximately 36% in one drilling application. Dynamic modeling of the BHA has identified the key design changes leading

to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA.The BHA design evaluation process uses a frequency-domain lateral dynamic model in both pre-drill forecast and

post-drill hindcast modes. BHA lateral vibrations are characterized such that alternative BHA configurations may be

developed and compared directly with a proposed baseline assembly. In the hindcast mode, the BHA model can be operated

at the recorded WOB and RPM to generate corresponding model results in time or depth, and these values can be comparedto the measured performance data.

In one case study, the redesign of a BHA with downhole motor and roller reamer is described, with corresponding field

data for four original BHAs and four redesigned assemblies. In a second application, model and field drilling results for two

rotary steerable assemblies are compared to evaluate the predictive ability of the model in smaller hole size and with different

BHA types. Finally, the utility of the model to identify preferred rotary speed sweet spots is demonstrated in a motor BHAoperating in larger hole.

IntroductionTwo prior publications describe the basic methodology that has been developed to model BHA lateral vibrations. The first

paper(3)provides a general description of the model and presents case studies of four field applications of this model. The

second reference(4) is a study of 13 BHA runs in the same field, for which slightly different BHA designs and operating

parameters were used. The Appendix of the second paper comprises a detailed mathematical description of the basics of thisfrequency-domain lateral vibrations model, known as VybsTM. The present paper illustrates the application of these methods

to a new set of BHA design problems in a joint study conducted by RasGas and ExxonMobil.

Briefly, the modeling process begins with an input panel that is populated with mechanical dimensions of the components

of the BHA, usually up to the heavy-weight drillpipe (HWDP), with about the same level of detail as a fishing diagram. It isimportant that the positions of the contact point constraints are entered correctly, and that the stiffness and inertial properties

of the assembly are a proper representation of the subject BHA. Then the desired operating parameters for drilling need to beprovided, including the anticipated ranges of bit weight (WOB) and rotation rate (RPM).

The linear modeling process considers a dynamic perturbation about the static state. The model employs two vibration

modes to compare and contrast the response of each candidate BHA design: lateral bending and twirl. In the lateral bending

vibration mode, an identical reference bit side force input is applied to each design, and the magnitudes of the response at

other locations along the BHA are compared. In the twirl mode, an identical mass eccentricity is applied to each modelelement to investigate the stability of the BHA to eccentric mass and centrifugal force effects.

Simulation results are plotted for multiple BHA designs simultaneously in 2D or 3D displays of state vectors. Index

values have been designed to summarize dynamic performance and are displayed for selected configurations to immediately

identify operating sweet spots as well as to indicate which design configuration may be preferred. The indices include BHA

Strain Energy and Transmitted Strain Energy to represent the dynamic bending strain in the BHA and HWDP, theStabilizer Side Force index to quantify the dynamic wall contact interaction forces, and the End-Point Curvature index to

represent bending at the top of the model in response to excitation at the bit. Since there is not a specific known nodal

IPTC 13349

Managing Drilling Vibrations Through BHA Design OptimizationJ.R. Bailey, SPE, ExxonMobil Upstream Research Company, and S.M. Remmert, SPE, RasGas Company Limited


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location in the free pipe above the BHA, a sensitivity analysis is completed where multiple possible node locations are

considered at the top end of the model, and the results are processed to identify average and worst case conditions. For the

flex lateral bending mode, the average value (RMS or root-mean-square) and the maximum value of the indices arecalculated for excitation at the various RPM multiples and end-length conditions, for each RPM and WOB state.

The model has been designed to characterize the vibration tendency of a BHA and to facilitate comparison of design

alternatives using a relatively straight-forward model. As will be shown in this paper, some BHA designs are preferred to

others from a vibrations perspective, and a more comprehensive solution is obtained rather than simply seeking to identify

and avoid the critical speeds of a given design. There are tangible benefits achieved by developing a simplified approach toBHA dynamics modeling. These include broad applicability, ease of use, minimized computing demand, and rapid

turnaround of new designs based on real time field observations. The model is an engineering tool that supports the decision-making process related to BHA design and selection, with an objective to mitigate lateral dynamic vibrations and

BHA-induced stick-slip. The tool also enables the development of best practices for BHA design and thus can be used as an

instructional device. Ultimately, we hope to deploy this model to the engineering desktop.

There are multiple synergies between this work activity and prior efforts to improve drilling performance as reported inthe references.(1,2) The following case studies will show the additional benefits that accrue from modeling BHA designs.

Case 1: Redesign of a 12-1/4-inch Motor BHAA minimal bend adjustable kickoff (AKO) motor assembly is a standard design for the 12-1/4-inch hole section in nearly

every well that RasGas (operator) drills. The introduction of roller reamers to the BHA design a couple of years ago resultedin a significant reduction in the need for back-reaming. Rotating off-bottom is both time-consuming and hazardous to

drilling equipment. However, in initial field applications, cracking of the roller reamer body was observed in more than adozen runs. In an attempt to address this problem, the roller reamer was relocated from within the BHA to a position above

one or two joints of HWDP. At about the same time, a near-bit stabilizer was removed on a trial basis. This stabilizer had

been used by previous drilling personnel

because it was deemed necessary to hold

angle in the long high-angle hold sections ofthese wells. Fig. 1 illustrates these two BHA

design configurations, labeled Standard

BHA and Redesigned BHA.

These design changes resulted in theelimination of roller reamer cracking,

enabling routine use of roller reamers in these

long intervals. The redesigned BHA hasbeen in steady use for almost two years with

excellent field results.Field data from four intervals drilled with

the standard design and four wells drilled

with the redesigned BHA show theperformance benefits of the configuration

change. Fig. 2 provides footage per day for

the four standard designs (red, with anaverage of 1038 ft/day) and the redesigned

configuration (blue, with an average of 1412

ft/day), representing an average increase of36%. It must be noted that all 8 runs used an

identical model of fixed cutter drill bit, and

the data is entirely from two similar rigs on

adjacent blocks drilling the same formations.Sustained performance improvement wasalso observed in two more wells that used a

slightly different bit design, shown in purple

triangles in Fig. 2.

Additional data showed improved resultswith the Redesigned BHA. As may be seen

in Fig. 3, there were two cracked roller

reamers in the eight wells, and both occurredin the standard assembly configuration.

Roughly speaking, the probability of cracking

the roller reamer was reduced from 50% to

0% due to the design change. The only BHA

Standard BHA

Redesigned BHA

Fig. 1. Configurations for the Standard BHA (red) and the Redesigned BHA (blue).

Standard BHA

Redesigned BHA

Fig. 1. Configurations for the Standard BHA (red) and the Redesigned BHA (blue).


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IPTC 13349 3

that did not make it to TD was the standard configuration, and the average run length for the redesigned configuration was

5225 ft, an increase of 15% over the Standard BHA. The bit grades show a significant reduction in outer gauge bit wear and

damage for the Redesigned BHA, despite the longer run requirements of the second group of wells. The bit grade differenceof 6.3 (standard) versus 3.8 (redesigned) is significant.

Wells 1 and 5 provide a representative contrast between Mechanical Specific Energy (MSE) data for the respective BHA

design configurations, as illustrated in Fig. 4. Experience has shown that it is important to maintain the MSE below 100 ksi,

and that the bit often survives difficult formations when this is accomplished. Continuously high MSE readings over 100 ksi

increase the risk of premature bit failure and may cause a trip before the bit reaches TD, as occurred in well 4.

Fig. 3. Bit grade, roller reamer condition, and bit run results for eight wells in study group.Fig. 3. Bit grade, roller reamer condition, and bit run results for eight wells in study group.

Upper B Section5150

5155

5160

5165

5170

5175

5180

5185

5190

5195

52000

10

20

30

40

50

60

70

80

90

100

Mechanical Specific Energy (ksi)

Standard BHA

Redesigned BHA

Fig. 4. Comparable wellbore sections for Wells 1 and 5 show MSE reductions for Redesigned BHA.

TrueV

erticalDepth

Upper C Section5200

5205

5210

5215

5220

5225

5230

5235

5240

5245

52500

10

20

30

40

50

60

70

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90

100


Standard BHA

Redesigned BHA

TrueVerticalDepth

Mid-Section, Clean Limestones

6100

6105

6110

6115

6120

6125

6130

6135

6140

6145

61500

10

20

30

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50

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Standard BHA

Redesigned BHA

TrueVerticalDepth

Upper B Section5150

5155

5160

5165

5170

5175

5180

5185

5190

5195

52000

10

20

30

40

50

60

70

80

90

100


Standard BHA

Redesigned BHA

Fig. 4. Comparable wellbore sections for Wells 1 and 5 show MSE reductions for Redesigned BHA.

TrueV

erticalDepth

Upper C Section5200

5205

5210

5215

5220

5225

5230

5235

5240

5245

52500

10

20

30

40

50

60

70

80

90

100


Standard BHA

Redesigned BHA

TrueVerticalDepth

Mid-Section, Clean Limestones

6100

6105

6110

6115

6120

6125

6130

6135

6140

6145

61500

10

20

30

40

50

60

70

80

90

100


Standard BHA

Redesigned BHA

TrueVerticalDepth

Having demonstrated above that, in a controlled group of wells, the Redesigned BHA performance was superior to the

Standard BHA, the design differences may be explored using the vibrations model. In particular, there were two changes in

the redesigned configuration. What is the effect of each change individually, and should more controlled drilling tests be

conducted to identify perhaps another configuration that is better than the Redesigned BHA?To address the question of the relative merits of the two separate changes, two additional configurations were entered into

the vibrations model. As shown in Fig. 5, one BHA was configured with no near-bit stabilizer below the motor, but this

design, shown in yellow, retains the roller reamer at its original position within the drill collars. Another design kept the

near-bit stabilizer but has the roller reamer above two joints of HWDP, illustrated in green. In applications of this model, it isuseful to color-code the various designs and then refer to the BHA simply by color.

Lateral dynamic bending model simulation results for a single operating point, consisting of a specific WOB, RPM, and

excitation mode, are shown in Fig. 6. In this chart, the x-axis is distance to bit, with the bit at the left edge as in Fig. 5. The1X excitation mode is shown; this mode is present in most high frequency data that we have seen. The topmost set of results

in Fig. 6 corresponds to the lateral displacement. The first spatial derivative is the tilt angle and that is shown next. The

bending moment and finally shear load complete the chart. Results are shown color-coded for each BHA configuration.


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Looking more closely at the shear load,

one may see that the perturbation side force

at the bit is identical for all configurations.Moving away from the bit, the responses are

quite different, depending on the

configuration. A discontinuity in the shear

load is seen as a vertical segment of the

response at points of stabilizer contact. Themagnitude of the vertical segment represents

the dynamic side force at the stabilizer,which would correspond to dynamic torque,

BHA whirl-induced stick-slip vibrations, and

stabilizer wear in a drilling BHA.

Fig. 6 is a detailed response at just oneoperating condition. To evaluate an overall

response, one needs to evaluate more

operating conditions, such as the entire RPM

range of interest.

Fig. 7 provides a complete response mapfor the beam shear load for each

configuration, at a specified bit weight, forthe 1X excitation mode. Again, the

perturbation at the bit is the same in all

cases, however the magnitudes of the red

and green BHAs show increased

interference at the near-bit stabilizer, and theresponse maps for the red and yellow

designs show higher amplitudes at the roller

reamer than the blue and green BHAs. This

amplification of the perturbation at the bit, inthe rotary speed range of interest, is an

indicator of higher vibrations. The flatter

response of the blue BHA is desirable, withminimal amplification at uphole locations.

In Fig. 7, there is a vector output for eachconfiguration at each RPM, for a single

mode of excitation. Vibration indices were

conceived to reduce the model results to afew scalars for each combination of WOB

and RPM. These vibration indices provide a

quantitative basis for comparing theresponse of alternative BHA configurations.

Fig. 8 illustrates several vibration indices

that are used in this analysis.In Fig. 8, the BHA Strain Energy Index

is the dynamic bending strain energy, per

unit length, calculated from the bending

moment shown in Fig. 6. The TransmittedStrain Energy is calculated the same way, forthe upper BHA which is usually the first few

joints of HWDP. The Stabilizer Side Force

Index is the sum of the dynamic contact

forces, which are the vertical line segmentsin the shear load seen in Fig. 6. The End-

Point Curvature Index is a measure of the

system output at the top of the model if oneconsiders a perturbation at the bit to be the

system input.

Standard BHA

No Near-Bit Stab

Move Roller Reamer

Redesigned BHA

Fig. 5. Two intermediate configurations were introduced in the model, No Near-Bit and Move RR.

Standard BHA

No Near-Bit Stab

Move Roller Reamer

Redesigned BHA

Fig. 5. Two intermediate configurations were introduced in the model, No Near-Bit and Move RR.

Displacement

Tilt Angle

Bending Moment

Shear Load

Distance to Bit (ft) Blue BHA has

smallest responseDynamic shear load discontinuityat contact points

WOB = 30 kips, 136 RPM, Mode 1X RPM

Reference Side Force Applied at Bit

Fig. 6. Displacement, tilt, bending moment, and shear load chart at a specific WOB, RPM, and mode.

Displacement

Tilt Angle

Bending Moment

Shear Load

Distance to Bit (ft)

Displacement

Tilt Angle

Bending Moment

Shear Load

Distance to Bit (ft) Blue BHA has

smallest responseDynamic shear load discontinuityat contact points

WOB = 30 kips, 136 RPM, Mode 1X RPM

Reference Side Force Applied at Bit


RPM DBIT

RPM DBIT

Contact Interferenceat Near-Bit Stabilizer

RPM DBIT

RPM DBIT

Contact Interferenceat Roller Reamer

WOB = 30 klbs

Mode 1X

Fig. 7. Beam shear load response for all configurations, at 30 klbs bit weight, for the 1X excitation.

RPM DBIT

RPM DBIT

Contact Interferenceat Near-Bit Stabilizer

RPM DBIT

RPM DBIT

Contact Interferenceat Roller Reamer

WOB = 30 klbs

Mode 1X

Fig. 7. Beam shear load response for all configurations, at 30 klbs bit weight, for the 1X excitation.


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IPTC 13349 5

A set of lateral bending indices for these

four BHA configurations, two run in the field

and two analyzed only with the model, areprovided in Fig. 9, for 30 klbs WOB. For each

RPM, the RMS average value is calculated

from the model results for each mode of

excitation, for the flex mode lateral bending

excitation. Here, the RMS average has beencalculated over modes 1X to 3X. Lower

vibration indices indicate less vibration andthus smoother operations.

As seen in Fig. 9, the dynamic vibration

indices are reduced by a factor of two, three, or

more from the red lines to the blue lines,depending on the specific index and the rotary

speed range to be considered. This result

indicates a significant reduction in the

predicted vibrations for the blue BHA.

From Fig. 9, one may make an assessmentof the approximate value of the individual

design modifications. The model resultssuggest that elimination of the near-bit

stabilizer and moving the roller reamer into the

HWDP provide almost the same amount of

reduction in BHA vibrations, and the results

are cumulative. It now seems unnecessary toconduct further field trials to evaluate the two

changes independently.

The drilling parameters, measured data, and

the calculated vibration indices may be plottedin data strips in well log format, referred to as a

log-mode plot. The data for well 1 is shown

in log-mode format in Fig. 10. The red bar inthe middle is a marker that separates run data

on the left from model predictions on the right,and we know immediately that this is the red

BHA. The MSE exceeds 100 ksi on a regular

basis; the plots for Fig. 4 are taken from thisdataset (and from Fig. 11). The maximum

lateral acceleration is typically about 5 gs.

The log-mode plot for well 5 is provided inFig. 11. The data axes have been scaled

identically to Fig. 10 to facilitate comparison.

The values for WOB and RPM are roughlycomparable, but there is a significant reduction

in MSE and LatMax compared to Fig. 10.

The MSE is about 50 ksi, and the maximum

lateral vibrations are typically 2-3 gs. TheRedesigned BHA drilled the interval moreefficientlythan the Standard BHA design.

The index tracks to the right of the blue bar

show that, in comparison to Fig. 10, there was

a significant reduction in the flex modeBending Strain RMS (1st column), Bending

Strain 1X result (2nd column), and End-Point

Curvature (3rdcolumn). It is interesting to notethat the Bending Strain twirl mode index,

shown in the last column, actually increased.

BHA Strain Energy

End-Point CurvatureBHA Sideforce

TransmittedStrain Energy

Fig. 9. Vibration indices for the 12-1/4-inch motor BHA redesign analysis.

BHA Strain Energy



BHA Strain Energy



Fig. 9. Vibration indices for the 12-1/4-inch motor BHA redesign analysis.

BHA Strain Energy Strain energy in the BHA due to

bending deformation

Good correlation to MSE

Lateral bendingexcitation at the

bit: NxRPM

for N=1,2,3

Transmitted Strain Energy Strain energy in the upper part of

the BHA due to bending

deformation

Endpoint Curvature Curvature at the last element of BHA


Stab Sideforces Summation of dynamic reaction

forces at the stabilizer contacts

WOB


BHA Strain Energy Strain energy in the BHA due to

bending deformation


Lateral bendingexcitation at the

bit: NxRPM

for N=1,2,3

Transmitted Strain Energy Strain energy in the upper part of

the BHA due to bending

deformation

Endpoint Curvature Curvature at the last element of BHA


Stab Sideforces Summation of dynamic reaction

forces at the stabilizer contacts

WOBWOB


Fig. 10. Log-mode display of data and model results for Standard BHA in Well 1.

WOB RPM MSE LatMax BendStrn Mode1 EndCurv Twirl

MeasuredDepth

Fig. 10. Log-mode display of data and model results for Standard BHA in Well 1.


MeasuredDepth


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This data can be plotted in another way

similar to the vibration index chart. Fig. 12 is

the DVDT (Drilling Vibration Data Test)plot for well 1. As seen in Fig. 12, four

quadrants are used to display the information.

The LatMax measured data from the

downhole MWD is the data plotted as pink

circles. Curve fits to the data may be plottedas the dark red line, in this case a linear fit.

Model results are plotted with black and bluex markers. In the top left quadrant of

Fig. 12, the Bending Strain Energy index is

plotted with the data as a function of RPM.

The black x markers represent the flexmode RMS values (here, for modes 1X-4X),

and the blue x symbols are for the twirl

mode results. The bottom left chart shows

this data plotted versus WOB.

The right quadrants in Fig. 12 show thedata plotted with model results for a virtual

sensor, wherein the virtual sensor in thisinstance is an accelerometer located at

approximately the same location as the sensor

in the tool. The virtual sensor provides

model results at a given point, whereas the

indices measure the system response in amore global sense. This feature may provide

better comparison with point sensor data.

The black x markers correspond to the

RMS average for the flex lateral bendingmode, and the blue x markers represent the

twirl mode results, as before. The y-axes are

all scaled to a maximum value of 10, the peakmaximum lateral acceleration in well 1, in

gs. In Fig. 12, it is apparent that the line fitto the data is more closely aligned with the

black flex mode bending strain energy than

with twirl.Fig. 13 is the DVDT plot for well 5,

formatted with data and scaled identically to

Fig. 12. It is apparent that the maximumlateral vibrations are considerably lower for

the blue BHA, with few values in excess of

3 gs. In this plot, the line fit to the data moreclosely tracks the twirl mode values and has a

different slope from the lateral bending flex

mode.

The closer correspondence of the blueBHA to the twirl mode is in agreement withthe log-mode comparisons. The design

change has appeared to result in a conversion

from a lateral bending flex response to a less-

damaging twirl response.The data supports the design process

whereby decisions are based primarily on the

flex mode values, with twirl used to provide asecondary assessment for designs with nearly

identical flex mode behavior. This is the first

such case to directly support this design

approach.

Fig. 12. DVDT display of data and model results for Standard BHA in Well 1.Fig. 12. DVDT display of data and model results for Standard BHA in Well 1.

Fig. 13. DVDT display of data and model results for Redesigned BHA in Well 5.Fig. 13. DVDT display of data and model results for Redesigned BHA in Well 5.

Fig. 11. Log-mode display of data and model results for Redesigned BHA in Well 5.


MeasuredDepth

Fig. 11. Log-mode display of data and model results for Redesigned BHA in Well 5.


MeasuredDepth


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IPTC 13349 7

Case 2: Comparative Assessment ofTwo Rotary Steerable AssembliesFor specialty directional drilling applications,e.g., longer horizontal departure wells, the

operator will sometimes choose rotary

steerable systems (RSS) for the drilling

assembly. In general, RSS results in the

12-1/4-inch section have been good.However, results in the 8-1/2-inch section

have been mixed, with some excellent runsand some other runs in which the assembly

was replaced with a conventional motor BHA

before reaching TD. Two recent RSS runs in

8-1/2-inch holesize are compared in order tohighlight differences in design with respect to

vibration indices and actual field results.

Fig. 14 illustrates two RSS tools, one

shown in orange and the other in purple. The

3D plot of beam shear load versus RPM anddistance to bit for a representative WOB and

an excitation mode of 1X RPM is alsoprovided. Note that the orange assembly

shows a high degree of amplification of the

response, whereas the purple BHA shows a

subdued, flat response.

The vibration indices are shown in Fig.15, where the max value (thin colored line) is

plotted in addition to the RMS value (thick

colored line). Here the RMS value is

averaged over all calculated excitation modes(1X to 3X) and all selected positions of the

top node location.

The vibration indices in Fig. 15 show thatthe orange assembly is not expected to drill

as well as the purple BHA. From priorexperience and model calibration, it is known

that BHA designs with End-Point Curvature

index values in the low single digits are likelyto drill well. Efforts to normalize the other

indices are in progress to enable further

understanding of absolute index performance.A summary of these two runs is provided

in Fig. 16. Corresponding to the model

results, RSS-1 experienced problems drillingout the shoe, and after making a few hundred

feet of hole with one intermediate trip to

replace MWD components it was laid down.

This hole section was then drilled with aconventional motor BHA.

On the other hand, RSS-2 completed its

interval of nearly 5000 ft with very low levels

of lateral vibrations, manageable stick-slip,

good directional control, and a sustainableROP of 50 ft/hour.

Fig. 17 illustrates the drilling results for

the RSS-1 assembly. MSE values wererarely below 200 ksi and were typically 300

ksi or more. Stick-slip was also continuously

high for this assembly.

Fig. 14. Two rotary steerable configurations for 8-1/2-inch holesize.

RSS-1

RSS-2

Fig. 14. Two rotary steerable configurations for 8-1/2-inch holesize.

RSS-1

RSS-2RSS-2

Vibration indices for

purple RSS-2 much

lower than those for

the orange RSS-1

Typically, this order of

magnitude difference

indicates very

different performance

purple down hereFlex BHA Strain Energy

Flex Stab Sideforce

Flex End-Pt Curvature

Flex Trans Strain Energy

Fig. 15. Vibration indices for the 8-1/2-inch rotary steerable system analysis.

Values for End-Point

Curvature of 3-5

Suggest GoodPerformance

Vibration indices for

purple RSS-2 much

lower than those for

the orange RSS-1

Typically, this order of

magnitude difference

indicates very

different performance


Flex Stab Sideforce




Flex Stab Sideforce



Fig. 15. Vibration indices for the 8-1/2-inch rotary steerable system analysis.

Values for End-Point

Curvature of 3-5

Suggest GoodPerformance

RSS-1

Experienced very high MSE values during drill out

Both high MSE & stick slip observed while drilling below casing shoe

Lateral vibrations exceeding 4gs with continuous stick-slip

Two runs failed immediately (internal communications failures)

Equipment & maintenance procedures OR vibrations ?

RSS-2

Drilled to section total depth, almost 5000 ft

Mostly low to moderate levels of stick-slip

Minimal lateral vibrations

Good directional control into tight target with ROP of ~ 50 fph

Final bit grade of 1-3-CT-S-X-I-CT-TD

Fig. 16. Summary of results for RSS-1 and RSS-2 runs.

RSS-1

Experienced very high MSE values during drill out

Both high MSE & stick slip observed while drilling below casing shoe

Lateral vibrations exceeding 4gs with continuous stick-slip

Two runs failed immediately (internal communications failures)

Equipment & maintenance procedures OR vibrations ?

RSS-2

Drilled to section total depth, almost 5000 ft

Mostly low to moderate levels of stick-slip

Minimal lateral vibrations

Good directional control into tight target with ROP of ~ 50 fph

Final bit grade of 1-3-CT-S-X-I-CT-TD

Fig. 16. Summary of results for RSS-1 and RSS-2 runs.


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The RSS-2 model results for the

measured drilling parameters, presented in

the log-mode display format, are provided inFig. 18. For the RPM and WOB used to drill

the section, calculated End-Point Curvature

indices were low relative to our experience-

based criteria, and the drilling results were

also good. One may observe a couple ofintervals of stick-slip, but overall there are

relatively low stick-slip vibrations.Fig. 19 shows the same data in the DVDT

format. In Fig. 19, the vibration indices are

plotted with the stick-slip data measurements

over a 1300-ft depth interval. This intervalincludes a stick-slip event towards the end of

the section. Note that in the DVDT display,

the model results are scaled in such a way

that the RMS averages of the two populations

are made equal.The plot of Fig. 19 has four quadrants.

Measured stick-slip vibration data is shownas the pink data circles, with the red quadratic

trend curves. The top row of plots has RPM

on the x-axis, and the bottom row is plotted

against WOB, as before. The charts on the

left side show Bending Strain Energy, and thecharts on the right show Transmitted Strain

Energy. Only blue x values are shown for

the twirl results for these indices.

With considerable scatter in the data,higher stick-slip values tend to be associated

with lower WOB and higher RPM. The

highest stick-slip values are observed forrotary speeds over 90 RPM and bit weights

less than 30 klbs. The data suggests that 30klbs may be a critical bit weight to suppress

BHA whirl in this interval. The results also

show that the twirl mode can be verysensitive to WOB, particularly for the upper

BHA indices, such as the Transmitted Strain

Energy shown on the right, but also the End-Point Curvature index (not shown). The

BHA Strain Energy index and the virtual

accelerometer (also not shown) indicate amore muted effect.

This data pattern reflects a condition

described as BHA whirl-induced stick-slip

and is consistent with the model results. It isinteresting to note that this observationoccurs at conditions opposed to bit-induced

stick-slip, and thus BHA whirl-induced stick-

slip should be taken into consideration in

both the design and operational phases.The overall assessment is that RSS-2 was

a successful run, whereas RSS-1 was not.

For this comparison, the vibration modelresults are in very good agreement with the

field results.

RPM Fluctuations

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 50 100 150 200 250 300 350

StickSlip

RPM at Bit

Fig. 17. Drilling data for RSS-1 shows very high MSE values and continuous stick-slip.

MSE (ksi)

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 200 400 600 800 1000 1200

MSE

High MSE values recorded

during drillout

High MSE and stick-slip

below casing shoe

Measured

Depth

RPM Fluctuations

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 50 100 150 200 250 300 350

StickSlip

RPM at Bit

RPM Fluctuations

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 50 100 150 200 250 300 350

StickSlip

RPM at Bit

Fig. 17. Drilling data for RSS-1 shows very high MSE values and continuous stick-slip.

MSE (ksi)

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 200 400 600 800 1000 1200

MSE

MSE (ksi)

13050

13100

13150

13200

13250

13300

13350

13400

13450

0 200 400 600 800 1000 1200

MSE

High MSE values recorded

during drillout

High MSE and stick-slip

below casing shoe

Measured

Depth

End-Pt

Curvature

Low ~ 1 to 4

WOB RPM StickSl ip BendStrn Mode1 EndPtCurv Twirl

Fig. 18. The Log Mode display for RSS-2 run, with low End-Point Curvature indices throughout run.

MeasuredDepth

End-Pt

Curvature

Low ~ 1 to 4



End-Pt

Curvature

Low ~ 1 to 4



MeasuredDepth

Fig. 19. Data from Fig. 18 plotted versus RPM (top row) and WOB (bottom row) for a 1300 ft interval.Fig. 19. Data from Fig. 18 plotted versus RPM (top row) and WOB (bottom row) for a 1300 ft interval.Fig. 19. Data from Fig. 18 plotted versus RPM (top row) and WOB (bottom row) for a 1300 ft interval.


9/10

IPTC 13349 9

Case 3: Sweet Spot Prediction for a 17-1/2-inch Motor BHAIt was noted in a morning report that one of therigs experienced a sweet spot around 90

RPM while drilling with a 17-1/2-inch motor

assembly that is used commonly in the field.

As a final case study, this observation is

investigated.A schematic of the BHA design is provided

in Fig. 20. The top stabilizer is considerablyundergauge, however, it is treated as a nodal

point in the model. Stabilizer contact at this

location along the assembly will cause it to be

a nodal point. Also shown in Fig. 20 is a 3Dmap of the 1X flex mode result for this design.

The line parallel to the DBIT axis represents

a slice along the BHA for a given operating

speed. The line at 90 RPM in Fig. 20 crosses

the tapered end of several humps, suggestingthat vibration mode peaks seen at higher speeds

may be avoided at 85-90 RPM.The Transmitted Strain Energy vibration

indices for the individual 1X, 2X, and 3X

modes are plotted in Fig. 21. One may note

that there is a considerable rise in the 1X shape

above 85-90 RPM, and the 90 RPM point isnear the right edge of a flat response extending

back to 55 RPM. However, the 2X mode is on

a decline from 60 RPM to 85 RPM, then it

gradually rises towards 110 RPM. Finally, the3X mode response shows a local minimum

near 85-90 RPM.

Thus, comparing the 3D chart in Fig. 20and the individual components of the lateral

bending vibration index in Fig. 21, the modelresults tend to support the field observation of

a sweet spot near 90 RPM.

Using the DVDT plot format, Fig. 22provides LatMax acceleration data, in gs,

for a 2870 ft run in the well in which the sweet

spot observation was made. The solid redcurve is a quadratic fit to the data, showing a

slight bowing tendency towards 85-90 RPM.

The data shown with the black x is theTransmitted Strain Energy, with the 1X mode

at top left, the 2X mode at top right, the 3X

mode at bottom left, and the RMS(1X-3X) at

bottom right.There is a reasonable correspondence

between the curve fit and the model results in

Fig. 22. A sweet spot near 90 RPM is indeed

plausible, given the model results and field

data shown in these charts. In this particularcase, the project team set two field records

(fastest 24-hour footage and best cycle time for

all 17-1/2-inch sections), attributable in part torotary speed optimization. The operator nowuses vibration model results in all pre-section

technical reviews in order to enhance field

optimization practices.

Model shows reduced

amplitude ~90 RPM

Fig. 20. Standard motor BHA for 17-1/2-inch hole and 3D response surface for 1X flex mode.

Model shows reduced

amplitude ~90 RPM

Model shows reduced

amplitude ~90 RPM

Fig. 20. Standard motor BHA for 17-1/2-inch hole and 3D response surface for 1X flex mode.

Fig. 21. Lateral bending indices (Transmitted Strain Energy Index)for individual excitation modes.

1X mode

3X mode

2X mode

Fig. 21. Lateral bending indices (Transmitted Strain Energy Index)for individual excitation modes.

1X mode

3X mode

2X mode

Fig. 22. Log-mode display for field run in which 90 RPM was cited as sweet spot.Fig. 22. Log-mode display for field run in which 90 RPM was cited as sweet spot.


10/10

10 IPTC 13349

SummaryBottom-hole assembly design improvement is an important component of vibrations management. It has been demonstrated

that better understanding and modeling of the influence of stabilizer and roller reamer placement on dynamic bending forcesand lateral stability enables development of improved BHA designs. A comparative modeling approach has been

implemented with an efficient frequency-domain vibration model to assess the relative vibration tendency of different

assembly designs, and the model results are closely aligned with field experience.

In the first case study, it was shown that the placement of roller reamers and stabilizers in a BHA design can significantly

affect BHA dynamics and drilling performance. Lower vibration indices are associated with higher daily footage, better bitgrades, and less damage to BHA components, in this case roller reamers. The second case study compared two rotary

steerable assemblies, one which ran a few hundred feet and was pulled for failing twice, showing excessive levels of lateralvibrations, stick-slip, and mechanical specific energy. The second RSS configuration drilled almost 5000 ft and achieved all

directional objectives. Model results showed significantly lower lateral bending flex indices for this design. The third case

study showed that both model and field drilling data agree with a rotary speed sweet spot for this BHA near 90 RPM.

In these studies, the relative influence of flex lateral bending and rotational twirl modes was considered, and it has beenfound that the most critical design objective is to reduce the flex mode indices to reduce lateral vibrations. In one case

study, the data suggests that twirl indices for the upper BHA can be used as a secondary assessment tool to evaluate the

potential for BHA-induced stick-slip tendencies of various design alternatives.

In these and several other case studies, it has been found that a relative performance assessment based on use of the model

is a good predictor of field results. The joint vibrations study has been integral to the operators drilling performancemanagement system and has resulted in close collaboration during the well design cycle.

AcknowledgementsThe authors are grateful for the support of ExxonMobil and RasGas Company Limited for permission to publish this paper.

We have continued to enjoy working with our co-authors of the previous papers referenced below, and we appreciate their

continued support and guidance. All figures in this paper are original figures created by ExxonMobil and RasGas Company

Limited.

References1. Dupriest, F. E., J. W. Witt, S. M. Remmert, and D. R. Aberdeen. Maxmizing Rate of Penetration with Real Time Analysis of Digital

Data. IPTC Paper 10706 presented at the 2005 International Petroleum Technology Conference, Doha, Qatar, Nov. 21-23.2. Remmert, S. M., J. W. Witt, and F. E. Dupriest. Implementation of ROP Management Process in Qatar North Field. IADC/SPE

Paper 105521 presented at the 2007 IADC /SPE Drilling Conference, Amsterdam, Feb. 20-22.

3. Bailey, J. R., E. A. O. Biediger, V. Gupta, D. Ertas, W. C. Elks, and F. E. Dupriest. Drilling Vibrations Modeling and FieldValidation. IADC/SPE Paper 112650 presented at the 2008 IADC /SPE Drilling Conference, Orlando FL, Mar. 4-6.

4. Bailey, J. R., E. A. O. Biediger, S. Sundararaman, A. D. Carson, W. C. Elks, and F. E. Dupriest. Development and Application of aBHA Vibrations Model. IPTC Paper 12737 presented at the 2008 International Petroleum Technology Conference, Kuala Lumpur,

Malaysia, Dec. 3-5.

spe-13349 managing drilling vibration through bha design optimizationiptc-13349-ms

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