1. INTRODUCTION

It is known that vibration combined with rotation

increases the rate of penetration in drilling relative to

conventional drilling, e.g. Wiercigroch M. studie

effect of resonance enhanced drilling [1];

showed that vibration can increase the rate of penetration

in rotary drilling [2]. However, from our investigation

decreases the bit life. The advanced drilling group in

Memorial University of Newfoundland has investigated

different aspects of bit performance in vibration drilling.

One of the important issues is bit wear and relating it to

bit performance, not just for the bit life, but also

of penetration. Miller and Ball classified bit wear as five

different types, “recently exposed or unworn diamonds,

wear flat, micofracture, hackly macrofracture, and pull

out hole” [3]. They did their experiments with different

types of rocks and found that “for stable drilling in any

given rock type a characteristic threshold pressure

existed above which desirable microfracture of the

exposed diamonds was promoted over undesirable wear

flat generation. At lower load, flats are produced by

sliding wear, with the silicate minerals ploughing plastic

grooves in the heated surfaces of the diamonds”

Wright, et al reported some results for drilling on two

different rock types. In drilling sandstone erosion of the

ARMA 11-266

Wear Analysis and Optimization on Impregnated Diamond Bits in

Vibration Assisted Rotary Drilling

Abtahi A., Butt S., and Molgaard J.,

Memorial University of Newfoundland, St. John’s

Copyright 2011 ARMA, American Rock Mechanics Association

This paper was prepared for presentation at the 42011.

This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and crithe paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the wriis prohibited. Permission to reproduce in print is restricted to an ababstract must contain conspicuous acknowledgement of where and by whom the paper was presented.

ABSTRACT: This is an investigation to find, understand, and optimize bit wear using

of embedded diamond bits is being studied with and without vibration, to better understand the mechanisms of wear, the effect

vibration on them, and to study relationships between drilling parameters including

profile, focusing separately on the wear mechanisms for the bit matrix and the embedded diamonds. Tests

the effect of different drilling conditions on bit matrix wear, diamond wear, and power consumption, working mainly with short

runs in which small amounts of wear occurred.

as uniaxial compressive strength and relative abrasion resistance, by varying the proportions and curing of the included materials.

Some preliminary results and observations are reported.

critical for rate of penetration (ROP) and bit life

minimum weight loss may overlap, but conditions for maximum ROP and minimum wear rate are

combined with rotation

in drilling relative to

Wiercigroch M. studied the

; also Li H. et al

that vibration can increase the rate of penetration

from our investigation it

he advanced drilling group in

ewfoundland has investigated

vibration drilling.

wear and relating it to

bit life, but also to rate

classified bit wear as five

, “recently exposed or unworn diamonds,

fracture, and pull-

. They did their experiments with different

“for stable drilling in any

given rock type a characteristic threshold pressure

existed above which desirable microfracture of the

osed diamonds was promoted over undesirable wear

lats are produced by

with the silicate minerals ploughing plastic

ted surfaces of the diamonds”. D.N.

drilling on two

sandstone erosion of the

matrix predominated, in particular around diamond

particles [4]. In both sandstone and granite

eventually pull out of the diamond particles. In the case

of granite, there were particles pulled out

fractured; with sandstone pull out occurr

fracture. With both rocks break

supporting matrix had been eroded.

“the rate of diamond protrusion can be directly related to

its position on the end face of bit and the rate of

exposure of diamonds related

matrix”. Xuefeng Tian, and Shifeng Tian

experimental studies on wear mechanism

drilling [5]. “A single-diamond

to understand the coefficient of friction and wear

at contact surface. The coefficient of friction depends on

rock fracture characteristics at the

found that the penetration per revolution was the

predominant parameter influencing wear behavior

They also found that wear depends on drilling conditions

and diamond temperature. Excessive penetration rate

increases temperature and it results

adhesion of diamond and drilling detritus

Wear Analysis and Optimization on Impregnated Diamond Bits in

Vibration Assisted Rotary Drilling (VARD)

Butt S., and Molgaard J., Arvani F.,

St. John’s, NL, Canada

ARMA, American Rock Mechanics Association

the 45th US Rock Mechanics / Geomechanics Symposium held in San Francisco, CA

This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and crithe paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect any position of ARMA, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the wriis 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 conspicuous acknowledgement of where and by whom the paper was presented.

to find, understand, and optimize bit wear using vibration assisted

of embedded diamond bits is being studied with and without vibration, to better understand the mechanisms of wear, the effect

between drilling parameters including rotational velocity,

, focusing separately on the wear mechanisms for the bit matrix and the embedded diamonds. Tests

ons on bit matrix wear, diamond wear, and power consumption, working mainly with short

runs in which small amounts of wear occurred. Concrete was selected as a rock analog as it can provide a range of properties, such

elative abrasion resistance, by varying the proportions and curing of the included materials.

Some preliminary results and observations are reported. Wear caused changes in bit profile. Effect of bit profile

and bit life. For a given profile, the ranges of the optimum WOB

conditions for maximum ROP and minimum wear rate are not always identical.

in particular around diamond

In both sandstone and granite were

pull out of the diamond particles. In the case

particles pulled out after they

; with sandstone pull out occurring before

With both rocks breakdown occurred when the

been eroded. They also found that

“the rate of diamond protrusion can be directly related to

s position on the end face of bit and the rate of

exposure of diamonds related to the abrasion of the

Xuefeng Tian, and Shifeng Tian did some

wear mechanisms in hard rock

was used for rock cutting

ent of friction and wear process

oefficient of friction depends on

the contact surface. It was

found that the penetration per revolution was the

minant parameter influencing wear behavior”.

They also found that wear depends on drilling conditions

and diamond temperature. Excessive penetration rate

increases temperature and it results in micro-burn and

adhesion of diamond and drilling detritus together.

Wear Analysis and Optimization on Impregnated Diamond Bits in

San Francisco, CA, June 26–29,

This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and critical review of any position of ARMA, its officers, or

members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA stract of not more than 300 words; illustrations may not be copied. The

assisted rotary drilling. The wear

of embedded diamond bits is being studied with and without vibration, to better understand the mechanisms of wear, the effect of

rotational velocity, vibration, bit pressure, and

, focusing separately on the wear mechanisms for the bit matrix and the embedded diamonds. Tests reported here, analyze

ons on bit matrix wear, diamond wear, and power consumption, working mainly with short

provide a range of properties, such

elative abrasion resistance, by varying the proportions and curing of the included materials.

bit profile. Effect of bit profile is found to be

WOB, the maximum ROP, and

not always identical.

2- EXPERIMENTAL MACHINE AND

MATERIALS

The laboratory drilling machine of VARD project is an

electrical powered drill rig with two rotary speeds of 300

and 600 RPM. The drill can easily move up and down on

a rail guide. The sample is mounted on an

electromagnetic shaker attached to the base, to vibrate

the sample at different frequencies and amplitudes

instead of vibrating the bit. A constant weight on bit

(WOB) is applied by hanging a weight from a wheel

(Fig. 1).

All data is saved on a computer including current,

vibration amplitude, and drilling depth, using a group of

accelerometers and LVDT. Water pressure and flow rate

is read during experiments from gauges. The LVDT is

attached to the table to register the amplitude of the

vibration and a frequency inverter is used to set the

frequency. Also a rotary encoder is attached to the drill

bit and travels with the bit along the rig frame to

measure the displacement or drilling depth for each

drilling. A tachometer is used for measuring the exact

rotary speed.

Concrete samples were used instead of rocks to have

identical samples in weight on the shaking table,

uniaxial compressive strength (UCS) values, and

abrasivity. The concrete mixture is shown below: ���� ������� 0.3 (1)

������ �������� 0.5 (2)

Concrete samples were cured in 23 degree Celsius and

100% humidity to reach the maximum UCS value. UCS

values tested in correspondence to ASTM C873after 7

and 28 days were respectively 35 and 38 MPa. Another

UCS test was done on core samples during the drilling

runs and the value was 46MPa.

3- PROCEDURES FOR WEAR MEASURMENT

Methods have been investigated and designed for

measuring the wear of the matrix and diamonds on

impregnated coring bits. A typical way of calculating the

volume of wear is through measuring the mass or length

of the bit. In this project, wear is being studied by

placing indentations on the surfaces and using replicas of

the surfaces. Replication is the best way to save all of the

bit information permanently after each test. Two types of

replica are being produced, using silicon rubber and

epoxy materials. They keep the full shape of the bit. First

a negative replica of the face of the bit is molded using

silicone mold-making resins then a positive epoxy

replica is cast in the negative replica (Fig. 2). The

positive replica is gold coated for use under optical

microscopes (Fig. 3).

Fig. 1. Drill rig

The replication method is very precise and it saves all of

the data such as profile shape, length, and size of the

head of the bit permanently. This makes it possible to

follow changes at any location on a bit throughout an

experiment without any concern regarding missing any

information or measurement after each experiment.

Fig. 2. Negative replica Fig. 3. Positive replica

Indentations are used as reference marks to aid accurate

measurements of changes in length and profile. Using a

center punch or electro discharge machining (EDM), it is

possible to make indentations on different locations on

the bit. Usually, indentations are placed on the water

way surfaces, bit end and side faces. Water ways can

show the profile changes and change in the length of

teeth (Fig. 4). Side face and end face can show depth

change in addition to change in position of the

indentation relative to bit face.

Fig. 4. indentation on waterway face

The bit surfaces before and after experiments were

compared, using pictures from the actual bit, taken from

end or side face with an optical microscope. In this case,

the best magnification is chosen first and then pictures of

the best places are captured.

4- EXPERIMENTAL PARAMETERS

Four new coring bits were used with dimension of

410mm length, 26.8 mm outside diameter, and 19mm

inside diameter. The mass of the new bit is 0.56 kg. The

end face area of the bit was 150���. For all the

experiments the constant parameters were, 60 Hz

vibration frequency, 600 RPM, and water flow rate of

3100 ��� ���⁄ with the supply pressure 4800 Pa. For

each experiment, other parameters of drilling such as

WOB, vibration amplitude and drilling depths were

varied.

In addition to the parameters just described, the bit

profile changes during drilling. Unused bits have a ‘V’

profile for the bit matrix with two sharp ridges (Fig. 5).

The ridges wear down quite quickly to two flats

separated by a groove (Fig. 7). With continuing wear the

profile changes to a complete flat (Fig. 6). Finally,

continuing wear changes the bit profile to rounded edges

(Fig. 8). The changes in profile may affect the

performance of the bit, but bits were used in all these

states.

Fig. 5. unused bit profile Fig. 6. flat end profile

Fig. 7. 2flat end with groove Fig. 8. rounded edge

5- RESULTS AND DISCUSSION

Preliminary tests were performed with several WOB

values, with vibration amplitude of 0.48mm and without

vibration (Fig. 9). A maximum ROP for each set of

conditions was found. The drill depths were 40mm for

each test, conducted in sequence in the same hole up to

total depth of 240mm. On the basis of these, subsequent

tests were performed with a drill depth of 100mm, each

in a separate hole and a WOB range from 60 to 111 kg,

within which a maximum ROP was expected.

Fig. 9. Effect of vibration on ROP on unused bit

Figure 10 and 11 shows effect of conventional (no

vibration) and vibration drilling. Figure 3 and 4 shows

the effect of different vibration amplitude levels on ROP

and weight loss. Each bit has a different profile shape.

For the first run of experiment (Fig. 10 and 11), bit 1 and

2 had flat end surface with edges a little rounded. Bit 3

and 4 had grooved end face, but bit 4 was in transition

from a grooved shape to a flat end; as shown in pictures

from waterways can display it very well (Fig. 12).

0.50

1.00

1.50

2.00

2.50

3.00

50 70 90 110 130

RO

P (

mm

/sec

)

WOB (kg)

bit 1, no vibration bit 2, vibration amplitude 0.48mm

Fig.10. Effect of vibration on ROP vs. WOB.

Fig.11. Effect of vibration on Weight loss vs. WOB.

Fig. 12. bit shape profile before experiment

Figure 13 and 14 show the effect of two vibration

amplitudes with different profile shapes. Bit 1 and 2 had

the flat end faces with rounded edges, and bit 3 was in

transition to a flat end face; bit 4 had a flat end face.

Fig.13. Effect of different vibration level on ROP vs. WOB.

Fig.14. Effect of different vibration on Weight loss vs. WOB.

Examination of the bits shows 3 major diamond

situations; unworn, fractured, and diamond pull out. For

the bits exposed to vibration pull out of diamonds was a

common wear pattern.

Generally, two types of wear occurred, matrix wear and

diamond wear. In this study, matrix wear was very

significant and it was associated with changes in the

ROP. Diamond wear just shows two main classes of

wear; diamond pull out and fracture. Matrix wear caused

the profile change. Profiles can be classified as grooved

(having two narrow flat end faces with a groove in the

center), flat end, and rounded edge. At each state, the

ROP was different, and the profile changed between

states, the ROP also changed. Figure 9 shows the ROP

for different WOB with two unused bits, bits 1 and 2.

Vibration drilling has almost 1.5 times more ROP than

conventional drilling. Fig.10 shows ROP for all four bits

with the same experimental conditions but with different

bit profiles. Bit 3 with the grooved profile had the

highest ROP (Fig. 12). Bit 2 with a flat end-face, had

intermediate range of ROP. Bit 4 was changing from

grooved shape to flat end face, and it had higher ROP

without vibration than bit 2 with vibration; this shows

1.501.701.902.102.302.502.702.903.103.303.50

50 70 90 110 130

RO

P (

mm

/sec

)

WOB (kg)

bit 1, no vibration bit 2 vibration amplitude 0.48mmbit 3 vibration amplitude 0.48mm bit 4, no vibration

0

0.05

0.1

0.15

0.2

0.25

0.3

50 70 90 110 130

wei

gh

t lo

ss (

g)

WOB (kg)

Bit 1, no vibration Bit 2 Vibration amplitude 0.48mm

Bit 3 vibration amplitude 0.48mm Bit 4, no vibration

2.00

2.20

2.40

2.60

2.80

3.00

3.20

3.40

3.60

50 70 90 110 130

RO

P (

mm

/sec

)

WOB (kg)

Bit 1 Vibration amplitude 0.38mm Bit 2 Vibration amplitude 0.58mm

Bit 3 Vibration amplitude 0.38mm Bit 4 Vibration amplitude 0.58mm

0

0.05

0.1

0.15

0.2

0.25

50 70 90 110 130

Wei

gh

t lo

ss (

g)

WOB (kg)

Bit 1 Vibration amplitude 0.38mm Bit 2 vibration amplitude 0.58mm

Bit 3 Vibration amplitude 0.38mm Bit 4 vibration amplitude 0.58mm

that with the ‘V’ profile the bit achieves a higher ROP.

Bit 1 was transitioning to a rounded edge (Fig. 12). This

had the lowest ROP compared with other shapes. Figure

11 shows the weight loss for the same experiments of

Figure 10; in which there is the same trend for all of the

bits; a decline from lower WOBs to higher WOBs.

Figure 13 and 14 shows the effect of different vibration

amplitude on bit performance; in this case bit 4 reached

the highest ROP with the flat end face. Bits 1 and 2 had

almost same profile, but different vibration amplitudes.

Bit 2 had a higher ROP than bit 1. Bit 3 was in transition

from a grooved shape to a flat end face, and it had higher

ROP than bit 1 with same WOB and vibration amplitude

but just difference in profile shape; it shows that the

transition situation also produced higher ROP. Figure 14

shows the weight losses for the same experiments as in

Figure 13. In this case weight loss increased a little up to

80kg WOB, but after that, it started to decrease with

adding more WOB.

Drilling productivity is affected by two critical factors in

conventional drilling, ROP and bit wear. Optimizing one

of them can affect the other one; Higher ROP usually

causes more wear. Another important issue is vibration;

it can assist drilling, increasing ROP, but it can affect bit

wear to an undesired rate. All of these factors should be

compared to obtain the best drilling conditions. For

example, in Figure 13, bit 4 has a highest ROP for the

range of WOB from 80 to 100 kg in comparison with the

other bits. It also has the vibration amplitude 0.58mm.

As seen in Figure 14, it has very low wear rate (weight

loss) for the range of WOB from 95 to 105. With these

plots, it is possible to choose the best condition; first,

compare profiles, then choose optimum range of WOB

for ROP, and lastly locate conditions for minimum wear

rate. This method can combine all of the factors that

contribute to an optimum.

The diamonds are, of course, the cutters, but the role of

wear of diamonds has yet to be studied in detail. The

main reason of matrix wear is diamond pull-out when a

bit loses diamonds, there has to be matrix wear to expose

new diamonds for cutting.

6- CONCLUSIONS

Optimum drilling productivity can be achieved by

optimizing both bit weight loss and ROP.

A decline in wear rate with increasing WOB was

observed when vibration was combined with rotation

Vibration is not the only variable that may cause

increased bit wear. Matrix wear leads to changes in

profile which, in turn, has a significant effect on ROP;

this study shoes profile change can be a more important

factor than vibration.

7- FUTURE WORK

Future work will include study of the effect of fluid flow

rate, as there in some evidence that this affects the

flushing of cuttings and matrix wear. We expect also to

check the effect of bit rotational speed and verify the

effects of varying vibration frequency and amplitude.

8- ACKNOWLEDGEMENT

This investigation has been funded by the Atlantic

Innovation Fund (contract no. 781-2636-192044),

Industrial Research and Innovation Fund, Husky Energy

and Suncor Energy.

REFERENCES

1. Wiercigrokh, M. 2007. Resonance enhanced drilling:

method and apparatus. World Organization patent no.

WO/2007/141550, filed June 06, 2007, and published

December 13, 2007.

2. Li, H., S. Butt, K. Munaswamy, and F. Arvani. 2010.

Experimental Investigation of Bit Vibration on Rotary

Drilling Penetration Rate. In the 44th US Rock

Mechanics Symposium and 5th U.S.-Canada Rock

Mechanics Symposium, held in Salt Lake City, UT June

27-30, 2010.

3. Miller, D. and A. Ball, 1990. The wear of diamonds in

impregnated diamond bit drilling. J. Wear. Res. 0043-

1648

4. Wright, D. N., S. M. Wilson, W. F. Brown, and U.

Ovens. 1990. Segment wear on diamond impregnated

mining bits. J. IDR industrial diamond review, ISSN

0019-8145.

5. Tian, X. and S. Tian. 1994. The wear mechanisms of

impregnated diamond bits. J. Wear. Res.0043-1648.