Ijmet 06 10_012

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 6, Issue 10, Oct 2015, pp. 103-114, Article ID: IJMET_06_10_012
Available online at
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=6&IType=10
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
STUDY OF SPECIFIC ENERGY METHOD
OF BIT SELECTION ON THE BASIS OF
DRILL BIT-DEPTH DATA IN UPPER ASSAM
OIL FIELDS
Mrinmoy Jyoti Borah
Department of Petroleum Engineering
AMET University, Chennai
ABSTRACT
Drilling bit is the most important and crucial tool for smooth and
economic drilling of an oil well. Achieving the desired rate of penetration with
the least possible bit wear and minimal hole problems is the goal of every
drilling engineer. Drilling engineers deal with many challenges before and
during drilling a new well even in a known area. There are many parameters
related to hardware and daily operations that are planned and also modified
as the drilling progress. Bit selection is one of the important parameters for
planning and designing a new oil or gas well. The aim of this research work is
to study and compare the performances of different drill bits in similar
formations by specific energy method of bit selection.
Key words: Drilling, Drill bit, Rate of penetration, Bit selection.
Cite this Article: Mrinmoy Jyoti Borah. Study of Specific Energy Method of
Bit Selection on The Basis of Drill Bit-Depth Data In Upper Assam oil Fields,
International Journal of Mechanical Engineering and Technology, 6(10),
2015, pp. 94-102.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=10
INTRODUCTION
Once it has been established that a potential oil-bearing structure exists, the only way
of confirming the existence of oil is to bring the oil to the surface and to do this we
have to drill a well. The process is called drilling and one of the most important
equipment used in this process is called drill bit. The drill bit represents the heart of
the drill string. The bit is the tool on the bottom of the drill string assembly that
actually drills the formation.
Achieving the desired rate of penetration with the least possible bit wear and
minimal hole problems is the goal of every drilling engineer. Drilling engineers deal
with many challenges before and during drilling a new well even in a known area.
There are many parameters related to hardware and daily operations that are planned

Study of Specific Energy Method of Bit Selection on The Basis of Drill Bit-Depth Data In
Upper Assam oil Fields
and also modified as the drilling progress. Bit selection is one of the important
parameters for planning and designing a new oil or gas well. The selection of a proper
bit is a difficult task since the factors affecting the bit performance are complex
relationships between formation properties, bit hardware design and operational
parameters.
A worldwide review of drilling performance has shown that 10 to 40% of the dry
hole cost of a well is mostly bit related which makes bit selection a vital issue. The
right rock bit for the right job cuts the cost of drilling. There are thousands of drilling
bits available in the market. Right selection of drilling bit is a very important thing to
get the best drilling performance and to reduce the cost of drilling. Correct bit
selection is becoming increasingly important; given the high cost of drilling a well
and the possible lower return from it, every effort must be made to drill faster and
further with every bit used.
Bit Selection Methods
Technological advances in bit design and cutter technology are greatly assisting
drilling engineers in bit selection for any given application. Nowadays great emphasis
is also given to petro-physical properties of formations for selection of appropriate bit,
since these properties have direct bearing on bit life. Compressive strength analysis
has been widely accepted as a key formation property for determining the drillability
of formations. Leading bit manufacturers like Hughes, Smith, and Halliburton
manufacture and supply bits based on formation characteristics (Compressive
strength). This requires formation logs in digitized form as inputs which are fed in
their software for the manufacture of a particular bit suitable for the formation.
There are several conventional methods prevalent for bit selection. They are as
follows:
 Cost per meter method.
 Dull bit grading method.
 Formation consideration method.
 Offset bit record method and
 Specific energy method.
As the study is completely based on specific energy method, we will concentrate on
the same.
SPECIFIC ENERGY METHOD
The specific energy method is a simple and practical method for the selection of bits.
Specific energy (SE) may be defined as the energy required removing a unit volume
of rock. The specific energy equation can be described by considering the mechanical
energy, E, expended at the bit in one minute. Thus,
E = W x 2πR x N. (I)
Where, W = weight on bit (lb).
N = rotary speed (rpm)
R = radius of bit (in).

Mrinmoy Jyoti Borah
The volume of rock removed in one minute is:
V = (πR2) x PR....................... (ii)
Where, PR = penetration rate in ft/hr.
Dividing equation (i) by equation (ii) gives specific energy in terms of volume as
=
= 10 in-lb/ (iii)
Replacing R by D/2, where D is the hole diameter, then equation (iii) becomes,
SE = 20 in-lb/
And in metric units,
SE = 2.35 MJ/
Where, W is in Kg; D is in mm; and PR is in m/hr.
Based on this method different drill bits having different IADC codes are
compared and their individual specific energy consumption is calculated in this study.
The bit that requires lowest specific energy for drilling is the best bit for drilling the
formation.
CALCULATIONS AND RESULTS
The study is divided into four cases viz. case A, case B, case C and case D. The cases
are classified on the basis of formation and bit size. The study was conducted on four
oil wells viz. BAGHJAN- 15, MKM-51, NHK-64, and MRN-116.
CASE A:
Formation: Sand/clay
Bit size: 12.15 inches
Type of Drilling: Directional Drilling
The study was carried out between BAGHJAN-15 and MKM-51.
Table 1 MKM-51
Type Of Bit Footage Per Day Cumulative Footage W In Kg
N In Rpm
W X N Daily Bit Hrs Cumulative Bit Hrs Specific Energy
12.25inch In meters In meters In MJ/
Bit type 1 397.536 397.536 8000 70 560000 12 12 127.5271402
527.424 924.96 8000 70 560000 29 41 232.2929065
533.32 1458.28 8000 70 560000 27 68 213.8817515
Bit Type 2 163.344 1621.624 8000 70 560000 15 83 387.9590711

SE
Cumulative footage
Graph 1 MKM-51
Table 1 shows the drilling bit-depth data from well MKM-51, where,
Bit Type 1is G-11FH (IADC: 1-1-7),
Bit Type 2 is G-12FH (IADC: 1-2-7).
From graph 1 it is clear that Bit Type 1 G-11FH (IADC: 1-1-7) with specific
energy 127.52 MJ/ with the other parameters has the lowest specific energy. It can
be accounted to the less daily bit Hrs. It should be noted that, though Bit type 2 was
signed for less footage per day and less bit hrs the specific energy consumption was
highest. Thus bit type 2 is not suitable according to specific energy method in this
type of formation. So let us check some other bit types in similar formations and
compare the suitability.
Table 2 Baghjan-15
Type Of Bit Daily Footage Cumulative Footage W In Kg N In Rpm W X N Daily Bit Hrs Cumulative Bit Hrs Specific Energy
12.25inch in meters in meters In MJ/
Bit type 1 479 479 16000 70 1120000 18.5 18.5 326.3352959
BIT TYPE 2 1297.896 1776.896 6000 95 570000 103 121.5 341.2573372
SE
Cumulative footage
Graph 2: Baghjan-15
Table 2 shows the drilling bit-depth data from well BAGHJAN-15, where,
Bit Type 1 is G11FH (IADC: 1-1-7)
Bit type 2 is PDC (Polycrystalline diamond compact) bit.

Mrinmoy Jyoti Borah
From Graph 2 it is clear that G11FH (IADC: 1-1-7) has lower specific energy than
PDC bit. But if we refer to table no 2, PDC bit was subjected to a high daily footage
but still the difference in specific energy between the two bits is just 15 MJ/ .
Result
If we compare both the wells, we find that G-11FH (IADC: 1-1-7) has the lowest
value of specific energy i.e. 127.52 MJ/ with the corresponding parameters (Table
1). But we also have to note that PDC bit with high daily footage, RPM, weight on bit
and highest daily bit Hrs consumes very less specific energy compared to the other bit
types. Thus, it can be assumed that a PDC bit with lesser footage, RPM, Bit Hrs will
consume much lower specific energy than G-11FH (IADC: 1-1-7). Thus from the
study we can say that PDC bit will prove to be suitable.
Now let us study the same formation (sand/clay) using the drilling-bit depth data
from the same two wells (BAGHJAN-15 and MKM-51) but with a different bit size.
The study was carried outbetweenBAGHJAN-15 and MKM-51.
CASE B:
Formation: Sand/clay
Type of well: Directional Drilling.
Table no 3 MKM-51
Bit type 1 5.904 5.904 4000 60 240000 5.5 5.5 2433.564169
53.136 59.04 3000 55 165000 9.5 15 321.0952723
251.904 310.944 4000 40 160000 27 42 186.6654334
BIT TYPE 2 503.808 814.752 3000 30 90000 47.5 89.5 92.36050091
BIT TYPE 3 738 1552.752 10000 50 500000 36 125.5 265.4797275
221.4 1774.152 10000 70 700000 37.5 163 1290.526453
246 2020.152 9000 80 720000 37.5 200.5 1194.658774
53.1 2073.252 10000 70 700000 3 203.5 430.4671288
SE
Cumulative footage
Graph no 3 MKM-51

Table no 3 shows the drill bit-depth data of a 8.5 inches bit in MKM-5 where,
BIT TYPE 1: SS-TMGP (1-1-7)
BIT TYPE 2: M1516 PX PDC
BIT TYPE 3: S 13GP (1-3-7)
From the graph, we get to know that M1516 PX PDC has the lowest specific
energy consumption i.e. 92.3 MJ/ in the whole drilling process. Now let us study
another well using 8.6 inches in same type of formation. After the study we can
compare between the two wells and analyze the optimum 8.5 inches bit for this type
of sand/clay formation.
Table no 4: Baghjan-15
Bit type 1 99.384 99.384 14000 75 1050000 19.25 19.25 2213.700079
BIT TYPE 2 57.072 156.456 14000 95 1330000 14.25 33.5 3614.586592
BIT TYPE 3 442.8 599.256 5000 90 450000 65.5 99 724.538423
BIT TYPE 4 47.232 646.488 14000 70 980000 14.5 113.5 3274.710875
43.2 689.688 12000 70 840000 12.5 126 2645.579229
BIT TYPE 1 10.824 700.512 12000 70 840000 4.25 130.25 1700.030287
SE
Cumulative footage FD
Graph no 4 Baghjan-15
Table no 4 shows the drill bit-depth data of 8.5 inches drill bit in Baghjan-15 where,
Bit type 1: G11FH (1-1-6)
Bit type 2: S13G (1-3-7)
Bit type 3: FC613 PDC
Bit type 4: HP43A (4-3-7)
It is seen that Bit Type 3, FC613 PDC has the lowest specific energy consumption
in the whole drilling process i.e. 724 MJ/ .

Mrinmoy Jyoti Borah
Result
After carefully comparing both the wells, it is seen that bit type 2 from MKM-51 i.e.
M1516 PX PDC consumes the lowest specific energy of 92.3MJ/ . It is to be noted
that in both the wells, PDC bit proves to be more optimum on the basis of specific
energy method. Thus we can say that for sand/clay formations in 8.5 inches bit size
category PDC bit proves to consume less specific energy and emerges as the most
suitable bit for drilling on the basis of specific energy bit selection method. Now let
us study a different type of formation using different sizes of drill bits.
CASE C:
Formation: sand/clay/coal/shale
Type of well: directional drilling.
The study was carried out on MRN-116 outfit: S8 and NHK-604 outfit: S-1.
Table no 5 MRN-116 outfit: s-8
Bit type 1 618.936 618.936 10000 80 800000 43.5 43.5 424.1732838
BIT TYPE 2 501.84 1120.776 10000 70 700000 59.91 103.41 630.4372941
351.288 1472.064 10000 70 700000 54.75 158.16 823.0546261
BIT TYPE 3 180 1652.064 15000 70 1050000 42.5 200.66 1870.318352
BIT TYPE 4 224.352 1876.416 15000 70 1050000 82.75 283.41 2921.710406
SE
Cumulative footage
Graph 5 MRN-116 outfit: s-8
Table no 5 shows the bit-depth data for MRN-116 outfit S8 where,
Bit type 1: G11FH (1-1-7) in sand/clay/coal
Bit type 2: G11FH (1-2-7) in sand/clay/coal
Bit type 3: XS4GS (2-1-7) in sand/coal/shale
Bit type 4: QH12S (4-3-7) in sand/coal/shale

From the graph it is seen that bit type 1 i.e. G11FH (1-1-7) has the lowest specific
energy i.e. 424.4MJ/ in case of sand/clay/coal formations.
But in case of shale formations bit type 3 i.e. XS4GS (2-1-7) has the lowest
specific energy. It should be noted that in shale formations the weight on bit increased
which requires more specific energy in drilling. As more weight on bit is applied in
formations, it directly adds up to the increase in specific energy.
Thus for shale formations, specific energy values are much higher.
Hence bit XS4GS (2-1-7) is more suitable than QH12S (4-3-7) while drilling shale
formations with the corresponding parameters according to specific energy method of
bit selection. Now let us study another well of same formation type using 12.25 inches
of bit for drilling.
Table no 6 shows you the drill bit-depth data of well no: NHK-604 OUTFIT: S-1
where,
Bit type 1: G11FH (1-1-7) in sand/sandstone
Bit type 2: PDC in sand/clay stone
Bit type 3: RC-137 in sand/clay/coal
Bit type 4: G12FH (1-2-7) in sand/sandstone/clay
Table 6 NHK-604 OUTFIT S-1
12.25 in meters in meters In MJ/
Bit type 1 100.368 100.368 5000 60 300000 7.33 7.33 165.2874085
Bit type 2 139.728 240.096 3000 90 270000 18.33 25.66 267.2099327
Bit Type 3 459.528 699.624 6000 90 540000 35.34 61 313.2983714
343.416 1043.04 7000 90 630000 35.16 96.16 486.6073917
Bit type 4 296.184 1339.224 12000 90 1080000 33.59 129.75 924.0212875
SE
Cumulative footage
Graph 6 NHK-604 OUTFIT S-1

Mrinmoy Jyoti Borah
From the graph, we see that bit type 1 has the lowest specific energy as the bit hrs is
less. Bit type 2 i.e. PDC bit has the second lowest specific energy but more than type
1 due to more weight on bit. Bit type 4 has the highest specific energy because it has
the highest weight on bit. Thus we can say that the more the weight on bit, the higher
is the specific energy.
Result
By comparing the graphs we note that, for sand/clay/coal formations, RC-137 has the
lowest specific energy of 313.2 MJ/ with the respective parameters and proves to
be the optimum one. Again for sand/coal/shale, XS4GS (2-1-7) proves to be more
suitable with respective parameters.
CASE D:
Bit size = 8.5 inches
Formation: sand/clay/coal/shale
Type of well: Directional drilling
The study was carried out between MRN-116 OUTFIT: S-8 and NHK-604 OUTFIT:
S-1.
Table 7 MRN-116 OUTFIT: S-8
Bit type 1 110.208 110.208 9000 65 585000 33.75 33.75 1949.987117
BIT TYPE 2 125.952 236.16 13000 60 780000 48.09 81.84 3241.600806
Bit type 3 120 356.16 13000 60 780000 51.33 133.17 3631.615331
BIT TYPE 4 122.016 478.176 15000 60 900000 61.83 195 4964.096236
BIT TYPE 5 218.448 696.624 6000 80 480000 68.42 263.42 1636.407474
BIT TYPE 6 50.184 746.808 12000 60 720000 19.5 282.92 3045.208639
SE
Cumulative footage
Graph 7 MRN-116 OUTFIT: S-8

Table no 6 shows you the drill bit-depth data of well no: MRN-116 OUTFIT: S-8
where,
Bit type 1: G11FH 1-1-6
Bit type 2: RC 137 1-3-7
Bit type 3: S13G 1-3-7
Bit type 4: HP43A 4-3-7
Bit type 5: FC613 PDC
Bit type 6: Q30S 5-3-7
From the graph it is seen that bit type 5 i.e. PDC bit has the lowest specific energy.
The highest specific energy is shown by bit type 4 which can be accounted to the
more weight on bit.
Table 8 NHK-604 OUTFIT S1
8.5inch IN meters IN meters In MJ/
Bit type 1 69.864 69.864 8000 65 520000 11.75 11.75 951.9255488
BIT TYPE 2 203.688 273.552 12000 75 900000 47 58.75 2260.425216
BIT TYPE 3 307.008 580.56 3000 90 270000 48.83 107.58 467.4293904
BIT TYPE 4 93.48 674.04 12000 65 780000 36 143.58 3269.592434
BIT TYPE 5 175.152 849.192 13000 65 845000 10.5 154.08 551.3738021
31.488 880.68 15000 75 1125000 30.25 184.33 11763.81117
32.472 913.152 15000 65 975000 6.5 190.83 2124.340623
SE
Cumulative footage
Graph 8 NHK-604 OUTFIT S1
Table no 8 shows the drill bit-depth data of well no NKH-604 outfit S1 where,
Bit type 1: G11F 1-1-6
Bit type 2: S13GP 1-3-7
Bit type 3: FC 613 PDC
Bit type 4: HP21G 2-1-7
Bit type 5: 5177051 (4-3-7)

Mrinmoy Jyoti Borah
From the graph w e come to know that bit type 3 i.e. FC 613 PDC bit has the
lowest specific energy consumption.
Result
By comparing both the graphs we come to a conclusion that, FC 613 PDC has the
lowest specific energy consumption in this type of formation with a specific energy
value of 467.4 MJ/ . It is also to be noted that the weight on bit on FC 613 PDC bit
was less but daily footage was the highest among both the wells. Thus we can say that
PDC bit proves to be the most suitable bit in this type of formation with the respective
parameters on the basis of specific energy method of bit selection.
CONCLUSION
From the study we have come to know that, weight on bit, daily bit hours and footage
per day plays an important role in deciding the specific energy of a drill bit. From
graph 2 we have seen that even a PDC bit with more bit hours and footage per day
demands a more specific energy input. So in any formation, we can achieve an
optimum specific energy input only by balancing the other drilling parameters. Thus
selection of a drill bit on the basis of specific energy mainly depends upon the type of
formation. It is obvious that a harder formation will require more specific energy
input than a soft formation. Moreover, we also came to know that PDC bit is
generally used in deeper and harder formations. The main advantage, we got to know
from the study is that, PDC bit can withstand high weight on bit as well as used for
more bit hrs and more daily footage without affecting the specific energy
consumption significantly. But the main disadvantage of PDC bit is that it is costlier.
So it will add up more value in cost per foot method in bit selection .So while
choosing a bit we have to consider the economic factors too. Thus we can say that,
specific energy method alone cannot be used to select a drill bit for drilling a well. We
have to take into account the economic factors, formation factors, log data too. Thus
we can conclude that, specific energy method together with other factors like
formation, economic factors etc can be suitably balanced to get an optimum drill bit
for a particular formation.
This study of drill bit-depth data will help future drilling operations in the subject
basins and give a detailed outlook towards the specific energy method of bit selection
to the drilling engineers.
REFERENCES
[1] Drill bit- Depth data provided for four wells in upper Assam oil basins by OIL
INDIA LIMITED, Duliajan, Assam
[2] "Wolfram (mathematical software) website: Drilling a square hole".
Demonstrations.wolfram.com. Retrieved 2014-05-10.
[3] "Practical demonstration of square-hole bit, YouTube video".
Youtube.com. Retrieved 2014-05-10.
[4] Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing
Processes Reference Guide, Industrial Press Inc., pp. 43–48, ISBN 0-8311-
3049-0.
[5] Modern machinery 5, Modern Machining Publishing Company, 1899,
p. 68.

[6] Stephen Ambrose Morse US patent 38,119 Improvement in Drill-Bits.
Twist Drill Bit, Granted: April 7, 1863
[7] McMaster-Carr catalog (115th ed.), McMaster-Carr, p. 2440, retrieved
2010-07-22.
[8] Oberg et al. 2000, pp. 829,846
[9] Oberg et al. 2000, p. 846
[10] Gillespie, Laroux (2008), Countersinking Handbook, Industrial Press Inc.,
pp. 78–79, ISBN 978-0-8311-3318-4.
[11] "Center Drill Chart. I-logic.com. Retrieved 2014-05-10.
[12] McMaster-Carr, p. 2438, 116th edition.
[13] P. Govinda Rao, Dr. C L V R S V Prasad, Dr.D.Sreeramulu, Dr.V. Chitti Babu
and M.Vykunta Rao. Determination of Residual Stresses of Welded Joints
Prepared Under The Influence of Mechanical Vibrations by Hole Drilling Method
and Compared by Finite Element Analysis, International Journal of Mechanical
Engineering and Technology, 4(2), 2013, pp. 542 – 553.
[14] T. Prabhu and Mr. A. Arulmurugu. Experimental and Analysis of Friction
Drilling on Aluminium and Copper, International Journal of Mechanical
Engineering and Technology, 5(5), 2014, pp. 130 - 139.

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