Salt and Anhydrite Full Version 01

Optimizing PDC Bits for Optimizing PDC Bits for Drilling in Salt and Drilling in Salt and AnhydriteAnhydrite

Hughes Christensen Hughes Christensen CompanyCompany

April 2001April 2001

The ChallengeThe Challenge

Designing PDC bits for cost effective Designing PDC bits for cost effective systems to drill salt and anhydrite systems to drill salt and anhydrite continues to challenge bit engineers.continues to challenge bit engineers.

Researchers investigate drilling Researchers investigate drilling mechanics with a full-scale laboratory mechanics with a full-scale laboratory drilling program and improve field drilling program and improve field performance with a new designs.performance with a new designs.

The Application in AlgeriaThe Application in Algeria

• ““Aggressive” bits drill softer rock the Aggressive” bits drill softer rock the fastest, but typically are not durable fastest, but typically are not durable enough for long interbedded sections.enough for long interbedded sections.

• Bits have low ROP in anhydrite.Bits have low ROP in anhydrite.

• Can performance be improved by Can performance be improved by balancing drilling efficiency with balancing drilling efficiency with durability?durability?

Algeria Field PerformanceAlgeria Field Performance

• Recent field performance shows the Recent field performance shows the effectiveness of a new approach for effectiveness of a new approach for drilling in Algeriadrilling in Algeria

• Fastest RunFastest Run

• Longest RunLongest Run

Drilling Technology LaboratoryDrilling Technology Laboratory

High-Pressure Drilling High-Pressure Drilling SimulatorSimulator

High-Pressure SimulatorCapabilities WOB 0 - 150,000 lbs.TOB 0 - 10,000 ft-lbs.

(750 hp motor)Rotary Speed 15 - 350 rpmROP 0 - 300+ ft/hrBorehole Pressure 6,500 psi @

500gpm or up to 10,000 psi @

200gpmSupply Pressure7,500 psi @ 500gpm

or up to 15,000 psi @ 200gpm

Confining Pressure 0 - 20,000 psiOverburden Pressure 0 - 20,000 psiFormation Pressure 0 - 20,000 psiDrilling Modes Constant ROP or

Constant WOBBit Size Up to 12 ¼"

High-Pressure SimulatorRock CoresDiameter 13 ½" , 15 ½" , 17 ½" , 20" , 20

½"Length 36" , 38"Rock Materials Commonly Used:Mancos Shale Berea SandstoneWellington Shale Crab OrchardCatoosa Shale Indiana LimestonePierre Shale Carthage MarbleMud SystemStorage: Four fiberglass tanks, 50bbl each, two

tanks with mechanical mixers mud mixed onsite, heat exchanger for temperature control

Mud Pumps Two Skytop-Brewster B1300T with 1,000 hp

SCR controlled motors

• 8-1/2” G445 20/20/15/30 .010” + 8-1/2” G445 20/20/15/30 .010” + CSECSE

• 8-1/2” G445 20/20/15/30 .016” + 8-1/2” G445 20/20/15/30 .016” + CSECSE

• 8-1/2” BD536 15/15/15/30 .010” + 8-1/2” BD536 15/15/15/30 .010” + CSECSE

PDC Bit SelectionPDC Bit Selection

• 8-1/2” G445 20/20/15/30 .010” + 8-1/2” G445 20/20/15/30 .010” + CSECSE

• 8-1/2” G445 20/20/15/30 .016” + 8-1/2” G445 20/20/15/30 .016” + CSECSE

• 8-1/2” BD536 15/15/15/30 .010” + 8-1/2” BD536 15/15/15/30 .010” + CSECSE

PDC Bit Design DetailsPDC Bit Design Details

•CSE Detail:

The TestsThe Tests

• 8 salt tests in 13.6 ppg SOBM8 salt tests in 13.6 ppg SOBM

• 1 salt test in 16 ppg SOBM1 salt test in 16 ppg SOBM

• 12 anhydrite tests in 13.6 ppg SOBM12 anhydrite tests in 13.6 ppg SOBM

The SaltThe Salt

• NaClNaCl22– From central UtahFrom central Utah

– 2.18 to 2.20 gm/cc density2.18 to 2.20 gm/cc density

– 3400 to 3900 psi UCS rapid loading3400 to 3900 psi UCS rapid loading

– 3000 psi 103000 psi 10-5-5 in/in/sec loading rate in/in/sec loading rate

– 5800 to 6200 psi confined strength (under 5800 to 6200 psi confined strength (under 5000 psi confining and 105000 psi confining and 10-4-4 and 10 and 10-5-5 in/in/sec loading rate, respecitively)in/in/sec loading rate, respecitively)

Rock and Dataprovided byTerratek

Observations Drilling in Observations Drilling in SaltSalt

• Salt is the softest mineral commonly Salt is the softest mineral commonly encountered in drilling. Drilling Strength encountered in drilling. Drilling Strength is in the laboratory tests was higher than is in the laboratory tests was higher than expected from rock strength testing.expected from rock strength testing.

• PDC bits tend to run off center in salt, PDC bits tend to run off center in salt, especially at light weight on bit.especially at light weight on bit.

• BitBit stability doesn’t appear to be an issue. stability doesn’t appear to be an issue.

Salt ROP and WOB Salt ROP and WOB ResponseResponse

BD536

0

50

100

150

200

250

0 5 10 15 20 25

WOB (kip)

RO

P (f

t/hr

)

120 rpm180 rpm

•6 ksi•13.6 ppg SOBM•.010” + CSE

Increasing Rotary Speed Increases ROP

Salt TOB and WOB Salt TOB and WOB ResponseResponse

BD536

0

2000

4000

6000

8000

0 5 10 15 20 25

WOB (kip)

TO

B (f

t-lb

)

120 rpm180 rpm

10

43

95

150

68

140

200


ROP (ft/hr)

Increasing rotary speed improves ROPwith little change in torque.

BD536

0

2000

4000

6000

8000

0 5 10 15 20 25

WOB (kip)

TO

B (f

t-lb

)

120 rpm180 rpm

System Limits Drilling SaltSystem Limits Drilling Salt


Max.

Vibration usually occurs beyond a threshold system limit and limits ROP.

10

43

95

150

68

140

200

Salt Drilling StrengthSalt Drilling StrengthBD536

010203040506070

0 5 10 15 20 25

WOB (kip)

SE (k

si)

120 rpm180 rpm

10

43

95 15068

140 200


•Specific Energy Calculation:

)(

)(

))()(480())(27.1(

Db

ROP

TRPMWOB

Es

Ideal drilling strength would be below 10,000 psi.

Variation in the Salt Variation in the Salt TestingTesting

0

50

100

150

200

250

300

350

0 10 20 30

WOB (lb)

RO

P (

ft/h

r) .010" R445SCRB R445.016" R445.010" BD536

•6 ksi•120 rpm•13.6 ppg SOBM

The BD536 outperforms the R445 designs at higher WOB.


0

50

100

150

200

250

300

350

0 10 20 30

WOB (lb)

RO

P (

ft/h

r) .010" R445SCRB R445.016" R445.010" BD536


Differences in performance aren’t as pronounced at higher RPM.


0

50

100

150

200

250

300

350

0 10 20 30

WOB (lb)

RO

P (

ft/h

r)

.010" R445SCRB R445.016" R445.010" BD536DP0391


Similar bits produce similar ROP.


0

50

100

150

200

250

300

350

0 10 20 30

WOB (lb)

RO

P (

ft/h

r)

.010" R445SCRB R445.016" R445.010" BD536DP0391



Mud Comparison Drilling Mud Comparison Drilling SaltSalt

0

50

100

150

200

250

0 10 20 30

WOB (kip)

RO

P (

ft/h

r) 120 rpm & 16 ppg120 rpm & 13 ppg180 rpm & 16 ppg180 rpm & 13 ppg

•6 ksi•120/180 rpm•SOBM

Performance is roughly the same.

BD536 ImagesBD536 Images


The BD536 produces large cuttings.


There is very little infiltration of the oil into the cutting.


Infiltration is mainly into fractures in the cutting.

R445 ImagesR445 Images


The G445 produces small cuttings that are easily broken apart.


R445 ImagesR445 ImagesOff-Center Rotation Off-Center Rotation TendenciesTendencies

Off CenterOn Center Forward Whirl

Rubbing of the matrix in between cutters absorbs WOB and reduces ROP.

ROP Limitations SummaryROP Limitations Summary

• Bit EfficiencyBit Efficiency– Low aggressiveness reduces ROPLow aggressiveness reduces ROP

• Energy Transmission (torque)Energy Transmission (torque)– Maximum system loading limits ROPMaximum system loading limits ROP

– System vibration limits ROPSystem vibration limits ROP

• Off-Center Rotation (Forward Whirl)Off-Center Rotation (Forward Whirl)– Matrix in between the cutters on blades rub and Matrix in between the cutters on blades rub and

limit ROPlimit ROP

SummarySummary

• Cost effective drilling of Salt requires a Cost effective drilling of Salt requires a bit design with good aggressiveness bit design with good aggressiveness and efficiency, but balanced with and efficiency, but balanced with durability for high torque and durability for high torque and vibration.vibration.

• Initial designs combining laboratory Initial designs combining laboratory and field experience have improved and field experience have improved ROP and durability in the field. ROP and durability in the field.

Drilling AnhydriteDrilling Anhydrite

• Rock CharacteristicsRock Characteristics

• drilling data 12 testsdrilling data 12 tests

Anhydrite ROP and WOB Anhydrite ROP and WOB ResponseResponse

BD536

0

20

40

60

80

100

0 10 20 30 40

WOB (kip)

RO

P (f

t/hr

)

120 rpm180 rpm


Increasing Rotary Speed Increases ROP

Anhydrite TOB and WOB Anhydrite TOB and WOB ResponseResponse

BD536

0

2000

4000

6000

8000

10000

0 10 20 30 40

WOB (kip)

TO

B (f

t-lb

)

120 rpm180 rpm


Increasing rotary speed improves ROP with constant torque.

BD536

0

2000

4000

6000

8000

10000

0 10 20 30 40

WOB (kip)

TO

B (f

t-lb

)

120 rpm180 rpm

System Limits Drilling System Limits Drilling AnhydriteAnhydrite


Max.

Vibration usually occurs beyond a threshold system limit.

Drilling StrengthDrilling StrengthBD536

0

100

200

300

400

500

600

0 10 20 30 40

WOB (kip)

SE (k

si)

120 rpm180 rpm


•Specific Energy Calculation:

)(

)(

))()(480())(27.1(

Db

ROP

TRPMWOB

Es

Ideal drilling strength would be below 10,000 psi.Efficiency improves with increasing ROP.

Variation in Anhydrite Variation in Anhydrite TestingTesting

0

10

20

30

40

50

60

0 10 20 30 40

WOB (lb)

RO

P (

ft/h

r) .010" R445SCRB R445.016" R445.010" BD536



ROP Drilling AnhydriteROP Drilling Anhydrite

0

20

40

60

80

100

120

0 10 20 30 40

WOB (lb)

RO

P (

ft/h

r) .010" R445SCRB R445.016" R445.016" BD536




0

20

40

60

80

100

120

0 10 20 30 40

WOB (lb)

RO

P (

ft/h

r)

.010" R445SCRB R445.016" R445.010" BD536DP0391




0

20

40

60

80

100

120

0 10 20 30 40

WOB (lb)

RO

P (

ft/h

r)

.010" R445SCRB R445.016" R445.010" BD536DP03917 bladeMX-1



BD536BD536.010” X 45 + CSE.010” X 45 + CSE

OB0001E

•Larger chips

•Wider cutter spacing

R445R445.010” X 45 + CSE.010” X 45 + CSE

OB0001C

•Small chips

•Small cutter spacing

R445R445Scribe cuttersScribe cutters

OB0001G

•Curved chips

•Scribed borehole pattern

R445R445.016” X 45 + CSE.016” X 45 + CSE

OB0001H

•Small chips

•Tight cutter spacing

12-1/4” HC60712-1/4” HC607? X 45 + CSE? X 45 + CSE

OB0001L

•Wide, small chips

•Kerfing borehole pattern

4 Blade4 Blade.? X 45 + ?.? X 45 + ?

OB0001M

•Wide, short chips

•Wide cutter spacing

BD536BD536.010” X 45 + CSE.010” X 45 + CSE

OB0002B


MX-1MX-1

OB0002F

•Very small chips

•Tracking and bottom balling

G445XLG445XL.005” X 45 + ?.005” X 45 + ?

ALG9902A

•Small chips

•Off center creates wide spacing

•Center balling

G445XLG445XL.005” X 45 + ?.005” X 45 + ?

ALG9902B

•Small chips

•Tight cutter spacing

BD536BD536?” X 45 + ??” X 45 + ?

ALG9902C

•Small chips


BD536BD536.? X 45 + CSE.? X 45 + CSE

ALG9902D

•Missing pictures

Key LessonsKey Lessons

• ROP performance is ROP performance is tied to bit efficiencytied to bit efficiency

• ROP can be increased ROP can be increased with Rotary Speedwith Rotary Speed

• Durability must be Durability must be taken into account for taken into account for high torquehigh torque

• Forward whirl can Forward whirl can reduce ROPreduce ROP

• Lower backrake and Lower backrake and smaller chamferssmaller chamfers

• Run higher rotary speed Run higher rotary speed while controlling while controlling vibrationvibration

• C/S must be robust as C/S must be robust as well as efficient for high well as efficient for high performance drillingperformance drilling

• C/S must resist forward C/S must resist forward whirlwhirl

Single Cutter Test Single Cutter Test MachinesMachinesTypical UsesTypical Uses

• Investigate fundamental behavior of Investigate fundamental behavior of individual cutters during drilling under individual cutters during drilling under simulated downhole conditionssimulated downhole conditions

• Acquire data used to improve Acquire data used to improve computer model of drill bit cuttingcomputer model of drill bit cutting

• Investigate drillabilitty of problem Investigate drillabilitty of problem formationsformations

Single Cutter Test Results Single Cutter Test Results

Non-Polished PDC Cutter Polished PDC Cutter

Catoosa Shale, 9000 PSI, 0.011 Inch Depth of Cut

0 2 4 6 8 10 12 14(200)

0

200

400

600

800

1,000

Time (sec)

Force (lbf)

AxialForce

TangentialForce

0 2 4 6 8 10 12 14(200)

0

200

400

600

800

1,000

Time (sec)

Force (lbf)

AxialForce

TangentialForce

Pressure Vesse l

Programmable LogicController (PLC)

Separation Vessel

PressureCompensator

Oil & Mud ControlCabinet

String Pot(Barely Visible)

LVDT(Behind Support )

Slip Rings

Single Point CutterTest Stand

Documents

Salt and Anhydrite Full Version 01