pdc dull grading

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IADC DULL GRADING SYSTEM FOR FIXED CUTTER BITS

Information provided by dull grading bits can be very significant.This value was recognized by theIADC some 25 years ago when aworldwide dull grading system for roller cone bits was established.

For fixed cutter bits - that is, all non-roller cone bits - this dullgrading system could not be applied,and a new system had to be estab-lished. The fixed cutter dull gradingsystem was developed by the IADCDrill Bits Sub-Committee in 1987 andrevised in 1991.

The fixed cutter dull grading sys-tem can be used for all non-rollercone bits, including natural dia-mond, polycrystalline diamond compacts (PDC), thermally stablepolycrystalline (TSP) diamonds,impregnated bits, core bits and non-roller cone bits which do not em-ploy diamond material as a cuttingelement.

The system does not distinguishbetween drilling and coring bits.This guide will only show examplesof PDC, TSP, natural diamond andimpregnated or sintered drill bits.

INTRODUCTION

IADC DULL GRADING SYSTEM CHART

Cutting Structure B G Remarks

Inner Outer Dull Bearing Gauge Other ReasonRows Rows Charact- Location Seals 1/16” Charact- Pulled

eristics eristics

X

The Dull Grading System Chartadopted by IADC includes all codesnecessary to dull grade roller conebits and fixed cutter bits.

The chart describes eight factorson drill bits. The first four spacesdescribe the

“Cutting Structure”

. Thefifth space

(“B”)

refers to “BearingSeals” and does not apply to fixedcutter bits. This space is alwaysmarked with an “X” when fixed cutter bits are graded. The sixthspace

(“G”)

refers to “Gauge Mea-surement” while the last two

“Re-marks”

spaces indicate “Other DullCharacteristics” (or secondary dullcharacteristics) and “Reason Pulled”.

Inner/Outer Rows

Using a linear scale from zero toeight, a value is given to cutters inthe inner and outer rows of surface-set bits to indicate the amount ofwear. Grading numbers increasewith amount of wear, with “zero”representing no wear and “eight”meaning no usable cutter left.Accordingly, “four” indicates 50%wear.

PDC cutter wear is measured in alinear scale from one to eight acrossthe diamond table, regardless of thecutter shape, size, type or exposure.

Figure 1

illustrates the cutter weargrading system schematically.

SYSTEM STRUCTURE

FIGURE 1

INNER AREA2/3 RADIUS

OUTER AREA1/3 RADIUS

When grading a dull bit, the average amount of wear for eacharea should be recorded. As shown above, 2/3 of the radius represents the “inner rows”. The five cutters in this areawould be graded “two”. This is calculated by averaging theindividual grades for each cutter in the area:

(4 + 3 + 2 + 1 + 0) = 250000

The average wear for the “outer” area is calculated in the samemanner:

(5 + 6 + 7) = 63000

“Six” would be the average wear gradient for the outer area.This information can now be transferred to the

IADC DullGrading System Chart

above.

NOTE: For a core bit, the centerline in Figure 1 would be theinside of the core bit ID.

Dull grading characteristics are based on PDC or stud wear, but also apply for TSP or Natural Diamond material. See photographs on the following pages.




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X

Dull Characteristics / Other Characteristics

The third and seventh spaces are foruse in noting dull characteristics ofthe bit, i.e., the most prominent phys-ical changes from its new condition.Codes for these characteristics arelisted below in

Table 1

. In general,four different wear characteristics can be distinguished for fixed cutterbits, as shown in

Figures 2A and 2B

.

FIGURE 2A. STUD CUTTERSTABLE 1.DULL/OTHER CHARACTERISTICS

FIGURE 2B. CYLINDER CUTTERS

*BC

- Broken Cone

BF

- Bond Failure

BT

- Broken Teeth/Cutters

BU

- Balled Up

*CC

- Cracked Cone

*CD

- Cone Dragged

CI

- Cone Interference

CR

- Cored

CT

- Chipped Teeth/Cutters

ER

- Erosion

FC

- Flat Crested Wear

HC

- Heat Checking

JD

- Junk Damage*

LC

- Lost Cone

LN

- Lost Nozzle

LT

- Lost Teeth/Cutters

NO

- No Major/Other Dull Characteristics

NR

- Not Rerunnable

OC

- Off-Center Wear

PB

- Pinched Bit

PN

- Plugged Nozzle/Flow Passage

RG

- Rounded Gauge

RO

- Ring Out

RR

- Rerunnable

SD

- Shirttail Damage

SS

- Self Sharpening Wear

TR

- Tracking

WO

- Washed Out Bit

WT

- Worn Teeth/Cutters

*Show cone number(s) under “Location”.

NOTE: If no “Dull Characteristic” is visible,mark this space “No”. If no “Other Char-acteristic” is visible, mark this space “No”.




eristics eristics

X

SYSTEM STRUCTURE

Worn Cutter (WT), Round TSP

Worn Cutter (WT), Round TSPBroken Cutter (BT), Round TSP

Worn Cutter (WT), Triangular TSPBroken Cutter (BT), Triangular TSP

Worn Cutter (WT), Mosaic

Broken Cutter (BT),Natural Diamond

Broken Cutter (BT), Triangular TSP




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Cored PDC Bit (CR)

Junk Damage (JD), PDC Bit

Ring Out (RO) on a TSP Bit

Ring Out (RO) on a PDC Bit

Balled Up (BU), Impregnated Bit

Erosion (ER) on a PDC Bit




eristics eristics

X

SYSTEM STRUCTURE

Worn Cutter (WT), PDC

Lost Cutter (LT), PDC

Worn Cutter (WT), PDCHeat Checking (HC), PDC

Chipped Cutter (CT), PDC

Chipped Cutter (CT), PDC

Erosion (ER), PDC




eristics eristics

X

Location

The “Location” space is used to in-dicate the location of the primary“Dull Characteristics” noted in thethird space. Four possible fixed cutter bit profiles are shown in

Figure 3

, along with the codes usedto identify commonly referred tolocations on the bit. One or more of these codes are used to indicatethe location of the dull character-istic(s) noted.

Bearing Seals

This space is used only for roller cone bits. Therefore, it will always be marked “X” when grading fixedcutter bits.

Gauge

The “Gauge (G)” space is used to re-cord the condition of the bit gauge.Record an “I” here if the bit is still ingauge. Otherwise, the amount thebit is undergauge is recorded to thenearest 1/16”. For specific undergaugemarkings, see

Figure 4

.

FIGURE 3. FIXED CUTTER BIT PROFILES

FIGURE 4. GAUGE CONDITION

Code Explanation

I In Gauge

1/16 Undergaugeup to 1/16”

2/16 Undergauge1/16” to 1/8”



TABLE 2. REASONS FOR PULLING BIT




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Reasons Pulled

The last space on the IADC DullGrading System Chart is used torecord the reason the bit was pulled.A list of codes is shown below in

Table 2

.

SYSTEM STRUCTURE

BHA - Change BottomholeAssembly

DMF- Downhole Motor FailureDSF - Drillstring FailureDST - Drill Stem TestDTF - Downhole Tool FailureLOG - Run LogsRIG - Rig RepairCM - Condition MudCP - Core PointDP - Drill PlugFM - Formation ChangeHP - Hole ProblemsHR - HoursPP - Pump PressurePR - Penetration RateTD - Total Depth/CSG DepthTQ - TorqueTW - Twist OffWC - Weather ConditionsWO - Washout Drillstring




eristics eristics

X

This S279 was used to drill a veryhard and abrasive sandstone forma-tion in the Rotliegendes in NorthernGermany. The special feature on thisbit is its Core Ejector (CE).

It drilled 100 meters in 51 hours on a 43/4” Mach 2 downhole motor at an average ROP of 2.0 m/hr, andwas pulled at 4750 meters to changethe BHA.

After pulling the bit, a uniformwear pattern was observed with the exception of the beginning of aring out on the bit shoulder. Eightwaterways were plugged with for-mation, which did not slow down the penetration rate. The bit was still in gauge.

The following examples show how to apply the IADC Fixed Cutter DullGrading System to worn bits.

Example 1

DULL GRADING WORN BITS

BIT INFORMATIONStyle: S279CESize: 5.875”TFA: 0.5

BIT INFORMATIONPulled Bit




eristics eristics

X

This R437GN was run in a horizontalwell to drill brittle to plastic shaleand sandstone. It drilled 387 metersin 29.5 hours with an average ROPof 13.1 m/hr on a Mach 1 AdjustableKick Off Motor. The bit was pulledat 1820 meters because of slow penetration rates.

This R437GN was run in a horizontaldrilling operation. The first run wasin shale on a 63/4” Mach 1 fixedangle-build motor.

The bit drilled 118 meters in 8.5 hours and was pulled at 1433meters. The ROP was 13.9 m/hr.

After the bit was pulled, no ob-vious wear could be seen, resultingin the IADC grading shown above.

The bit was re-run on another well in the same field in the same formation, drilling 218 meters in 13.5 hours for an average ROP of 16.2 m/hrs.

The bit was pulled when the bottomhole assembly had to bechanged.

When dull grading the bit, littlewear on the cutting structure wasseen, resulting in a dull grading of 1 for “inner / outer rows”. Threecutters were lost due to matrix erosion from a high flow rate, asshown in the “Dull” and “OtherCharacteristics” columns. The bitwas still in gauge, as indicated by “I” in the “Gauge” column.


Example 2

Example 3




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X




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X

Dull grading for the rerun bit.

BIT INFORMATIONStyle: R437GNSize: 8.5”TFA: 0.6

This S725 BallaSet bit with cylindri-cal TSPs was used to drill claystoneand sand in the medium hard anddense Rotliegendes formation inHolland. It drilled 154 meters in 57hours, achieving an ROP of 2.7 m/hron a Mach 2 downhole motor in adirectional well. The bit was pulleddue to a slow rate of penetration.Dull grading indicated the cutterswere worn 75% and 100% on theinner and outer rows, respectively.In addition, a ring out can be seen inthe taper area. The bit was also 1/16”undergauge due to abrasive sands in the formation.

Upon pulling the bit, it became ob-vious why the bit had ceased drilling— it was cored out and had lost all four nozzles. The remaining cuttersdid not show any significant wear.

NOTE: Although the bit lost all four nozzles, the primary “Dull Characteristic” is “cored” because this is the main reason the nozzles were lost. Lost nozzles are recorded under “Other Characteristics”.




eristics eristics

X

BIT INFORMATIONStyle: R437GNSize: 8.5”TFA: 0.6

BIT INFORMATIONStyle: S725GNSize: 8.38”TFA: 0.10

Example 4




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Run 2

Run 3

Run 4

This R435SG was run four times inthe North Sea area. The bit drilled a total of 977 meters in 166.3 hours,mainly in salt/anhydrite formationsof the Zechstein. Three of the fourruns were on a Mach 1 DTU motorwith RPMs of 210 to 320.

Dull grading of the first two runsshows no visible cutting structurefailure. The “Reason Pulled” wasDownhole Tool Failure (DTF) in bothcases. After the third run (389 metersin 89.5 hours ), the bit was pulled dueto BHA prob-lems, and showed a uniform wear pattern of

5

20% wearfor the inner and outer rows. Whenpulled after run four, the cuttingstructure wear was 50% and 60% forthe inner and outer rows, respective-ly. After four runs, the bit alsoshowed some severe erosion and lostcutters in the taper area.

(See phototaken after run 4)

Practical Applications.

The IADC Dull Grading Systemcan be used for multiple purposes.Manufacturers evaluate bit designand bit application. Operators eval-uate and improve their drilling pro-grams. The system can be computer-ized to build up a worldwide data-base in order to coordinate bit applications.

The main objective of the dullgrading system is to draw a

“stan-dardization picture”

of a bit, regardlessof where, or under what circum-stances the bit may have been used.This standardization is expected to lead to better bit application anddesign throughout the industry.


Example 5

X

X

X

BIT INFORMATIONStyle: R435SGSize: 12.25”TFA: 0.65 - 1.60

References:

SPE/IADC Papers 16142, 16145 and 23939.

©1996 Hughes Christensen Company. The emblems , and Hughes, Christensen, Eggbeater, Kingcutter and BallaSet are registeredtrademarks of Hughes Christensen Company. Black Ice, CSE, ECP, Mosaic, and SEC are trademarks of Hughes Christensen Company.

Printed in U.S.A. WL / 6M US / 4M A4 / 6-96

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