PDC Bit Dull Grading

Dull Grading:

Prepared by:

Mohd Zulkhairi M Z

[outlines]

PDC bit - overview Dull Grading-overview IADC Dull grading system chart

Inner/outer row cutting structure Dull characteristics Location Gauge Reason pulled

Dull grading: example Field application: SMDK-A5/ SMDK-A7 Conclusion

PDC Bit overview

PDC

Cutters

Profile

Gauge

Bit Breaker

Slot

API Threaded

Pin

Junk Slot

TFA Design

From DBS Bit

Blade

PDC Bit overview

Blade 3

Blade 4

Blade 1

Blade 5

Junk

slot Nozzle

Blade 6

Dull Grading-overview

IADC fixed cutter dull grading system

Developed by IADC in 1987- revised 1991

Applied for all fixed cutter bits

PDC

Natural Diamond

Impregnated Diamond

Bit record- in 1984

Old dull grading system (before 1987)

[example from Malong SG17.2 appraisal well]

Not descriptive

T- teeth B- bearing G- gauge

Why??

To draw a quick view of bit condition by using visual inspection and measuring tool.

When??

Primary- just after the bit was pulled out of hole

Before rerunning back the used bit

Dull Grading-overview

IADC Dull grading system chart

Applied for both fixed cutter bits and roller cone bits

First 4 spaces describes cutting structure

B is for bearing and G for gauge

Remarks indicate other dull characteristics and reason pulled

Inner

Rows

Outer

Rows

Dullcharac-

teristics

Othercharac-

teristics

Reason

pulled

Cutting Structure B G Remarks

InnerRows

OuterRows

DullCharact-eristics

Location BearingSeals

Gauge(1/16)

OtherCharact-eristics

ReasonPulled

X

8-Total lost

of tooth

height

0-No lost

of tooth

height

Grading numbers increase with amount of wear, with O

representing no wear, and 8 meaning no

usable cutters left. A grade of 4 indicates

50% wear.

[Brandon B.D.et al, IADC/SPE 23939]

-Round cutter

- Oval cutter


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

Inner Rows

Outer Rows

2 6

(Does Not include gauge cutters)

Typical IADC PDC WEAR GAUGE.


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

19 mm @ in

Diameter

13mm @ in

Diameter

19 mm @ 1in

Diameter

38mm @ 1 in

Diameter

Available PDC

cutting sizes

8,13,16,19,24 mm


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

BF - Bond Failure

BT - Broken Teeth/Cutters

BU - Balled Up

CR - Cored

CT - Chipped Teeth/Cutters

ER - Erosion

HC - Heat Checking

JD - Junk Damage

LN - Lost Nozzle

NR - Not Rerunnable

PN - Plugged Nozzle/Flow Area

RO - Ring Out

RR - Rerunnable

WO - Wash Out on Bit

WT - Worn teeth/Cutters

LT - Lost Teeth/Cutters

NO - No Other Major Dull

Characteristics

Du

ll C

ha

racte

ristics

*Only PDC relevant code are shown


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

Locatio

n o

f the p

rimary

DC

G gauge

S shoulder

N nose

C cone

T taper

A all areas


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

Code Explanation

I In Gauge

1 Undergauge

up to 1/16

2 Undergauge

1/16 to 1/8

3 Undergauge

1/8 to 3/16

4 Undergauge

3/16 to 1/4

* Use ONLY PDC gauge ring!!

( 4/16) undergauge

Measure the

gap between

ring gauge and

gauge cutter


InnerRows

OuterRows



Gauge(1/16)


ReasonPulled

X

BHA - Change Bottomhole Assembly

DMF - Downhole Motor Failure

DSF - Drillstring Failure

DST - Drill Stem Test

DTF - Downhole Tool Failure

LOG - Run Logs

RIG - Rig Repair

CM - Condition Mud

CP - Core Point

DP - Drill Plug

FM - Formation Change

HP - Hole Problems

PP - Pump Pressure

PR - Penetration Rate

TD - Total Depth/CSG Depth

TQ - Torque

TW - Twist Off

WC - Weather Conditions

WO - Washout Drillstring

Re

aso

n p

ulle

d

Bond Failure [ BF ]

Occur when cutter failing along the bond between two carbide substrates

Formation too hard for the selected bit

Bit may bouncing due to formation changes

Dull characteristics

Broken teeth [ BT ]

Cutting element is considered broken when 1/3 of the cutting element is broken to the

substrate

Caused by lack of bit stability

Balled up [BU]

A condition where formation attached to the blade and bit body/face of the cutters

May results in reducing ROP

Create physical damages to bits body

Rotary torque as the bit balls up


Washed out [ WO ]

Occur when drilling fluid eroded a passage from internal to external area

May results in twist off

Causes Ppump and ROP

Cored [ CR ]

A bit is considered cored if its centermost cutting elements are worn, broken or lost

The cone area will show a significant wear from the formation


Heat checking [ HC ]

Normally seen as cracks intersecting cutting elements

Cracks initiated due to thermal shock/fatigue

Can be seen at all areas: nose, shoulder, gauge

Ring out [ RO ]

A bit is said to have ring out when a circular band of cutting elements are

worn, broken or lost.

The blade will show a significant wear from the formation.

Always associated in Ppump &ROP


Plugged nozzle/waterway [ PN ]

A characteristics when one/more nozzles are obstructed

Always associated in Ppump

Worn Teeth [WT]

A condition where bit height reduces

due to cutting action

Exhibit smooth wear

characteristics


Lost Nozzle [ LN ]

Describes a bit that missing one or more jet nozzles.

Only stated at remarks column as LN

Caused by improper installation

Lost Teeth [LT]

No portion of cutter remain

Graded as 8 in cutting

structure

Caused by overload

condition


Erosion [ ER ]

Usually occur around cutters

Caused by several factors: body material, nozzle orientation, mud properties

Often a secondary characteristics

Junk Damage [JD]

Junk damage when contact with object other than formation

Caused by foreign object in the hole


Chipped Teeth/Cutters [ CT ]

Minor damage to diamond table and substrate

Caused by impact damage

Example A

R437GN was run in horizontal well

1st run: drilled 118 m in 8.5 hrs,

ROP = 13.9 m/hr

2nd run: drilled 218 m in 13.5 hrs,

ROP = 16.2 m/hr

Formation type: n/a

R437GN was run in horizontal well

Drilled 387 m in 30 hrs

ROP = 13.1 m/hr

Formation type: brittle to plastic shale/sandstone

Example B

R435SG was run 4 times in North Sea

Total footage drilled =977m in 166 hrs

Formation type = salt / anhydrite

Example C

SMDK-A7 12 PDC

IR OR DC L B/S G O/C R/P

0 1 CT S X IN NO TD

Smith

M75HKLSBPX

SMDK A5-8 PDC

IR OR DC L B/S G O/C R/P

0 0 NO A X IN NO TD

Varel VB552-MG2

Conclusion/Recommendation

Dull grading is vital in drilling campaign in order to evaluate the overall bit performance

A thorough research should be conducted to optimize the bit performance

For your reading pleasure: www.smithbits.com

www.bakerhughes.com

www.varelintl.com

SPE/IADC papers 16142,16145 and 23939

DIMS-Bit record

Thank you

PDC Bit Dull Grading

Documents

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