Drilling Efficiency and Stability Comparison Between Tricone, PDC and Kymera Drill Bits
Drilling Efficiency and Stability Comparison Between Tricone, PDC and Kymera Drill Bits
Drilling Efficiency and Stability Comparison Between Tricone, PDC and Kymera Drill Bits
MASTER’S THESIS
Writer:
Gergana Nikolova Karadzhova Gergana Nikolova Karadzhova
(Writer’s signature)
Faculty supervisor:
Jostein Håvard Kolnes
External supervisor(s):
Thorsten Schwefe
Thesis title:
Drilling efficiency and Stability Comparison Between Tricone, PDC and Kymera Drill Bits
Credits (ECTS):
30
Key words:
PDC Pages: …67………………
Kymera
TCI enclosure: …………
Efficiency
Stability
Vibrations Stavanger, 16.06.2014
Date/year
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Abstract
The primary object of this thesis is to analyse and optimise the drill bits performance that used to drill on the
Norwegian Continental Shelf. The three different types of bits that were utilized under drilling are described in
the first part of the thesis. The different aspects of designs and features are discussed and their technological
advantages are highlighted.
In the second part of the thesis an experimental tests are conducted. The main purpose of this test is to evaluate
the performance, efficiency and stability of 9 ½ inch Kymera (KM623), against 9 ½ inch PDC (6 bladed), and 9
½ inch (TCI) VMD - 20. The test will compare the drillability (ROP), durability (dullgrade, wear etc) and
stability of Kymera vs PDC and TCI. All the bits will be tested in the same formation types and strenghts at the
same range of RPM and ROP parameters. Bit response, stability and MSE will be evaluated in order to better
understand bit behavior in the subject formation. The analyses and conclusions will be used for future field
drilling optimization and advice in offshore operations.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Acknowledgment
First of all I would like to thank Baker Hughes for providing me with all the required data needed for this report.
I would like especially to thank my supervisor in the company Regional Drill Bit Engineer – Thorsten Schwefe.
My thanks goes to all the drill bit design crew that made experimental testing possible in Houston – Adam
Bohanan, Shana Larson.
I am gratefull to Professor Jostein Håvard Kolnes at the University of Stavanger for the support and useful
information.
At last would like to thank my family for been patient and supportive under this stressful part of my life.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
1 Innholdsfortegnelse
FACULTY OF SCIENCE AND TECHNOLOGY ............................................................................................... 1
MASTER’S THESIS ............................................................................................................................................. 1
ABSTRACT ........................................................................................................................................................... 2
ACKNOWLEDGMENT ....................................................................................................................................... 3
1 INNHOLDSFORTEGNELSE .................................................................................................................... 4
2 INTRODUCTION ....................................................................................................................................... 8
2.1 HISTORY ..............................................................................................................................................................8
2.2 SCOPE AND OBJECTIVE......................................................................................................................................8
3 DRILL BIT TECHNOLOGY OVERVIEW .............................................................................................. 9
3.1 POLYCRYSTALLINE DIAMOND COMPACT BITS (PDC) .................................................................................9
3.1.1 The PDC bit elements ..................................................................................................................................... 9
3.1.2 Cutting structure ...........................................................................................................................................10
3.1.3 Diamond Table Properties ........................................................................................................................12
3.1.4 Diamond/Carbide Interface .....................................................................................................................12
3.1.5 Edge Geometry ................................................................................................................................................12
3.1.6 Polished Cutters ..............................................................................................................................................13
3.1.7 Cutting mechanics .........................................................................................................................................14
3.1.8 Depth of Cut ......................................................................................................................................................14
3.1.9 Cutter size .........................................................................................................................................................14
3.2 THE BIT BODY .................................................................................................................................................. 15
3.2.1 The shank ..........................................................................................................................................................15
3.2.2 Bit body material ...........................................................................................................................................15
3.3 PDC DESIGN TECHNOLOGY........................................................................................................................... 16
3.3.1 Profile Theory ..................................................................................................................................................16
3.3.2 Profile Components.......................................................................................................................................16
3.3.3 Blade design .....................................................................................................................................................17
3.4 HYDRAULICS .................................................................................................................................................... 18
3.4.1 Hydraulic Design............................................................................................................................................18
3.4.2 Hydraulic Efficiency......................................................................................................................................18
3.5 PDC CUTTER FAILURE MODES .................................................................................................................... 19
3.5.1 Fracture .............................................................................................................................................................19
3.5.2 Chipping .............................................................................................................................................................19
3.5.3 Spalling ...............................................................................................................................................................19
3.5.4 Wear ....................................................................................................................................................................19
3.5.5 Heat Checking .................................................................................................................................................19
3.5.6 Diamond lip ......................................................................................................................................................19
3.5.7 Delamination ...................................................................................................................................................20
3.5.8 PDC bit Nomenclature .................................................................................................................................20
3.6 TRICONE BITS .................................................................................................................................................. 21
3.6.1 Roller cone legs ...............................................................................................................................................21
3.6.2 Roller cone bit types .....................................................................................................................................22
3.6.3 Bearings .............................................................................................................................................................23
3.6.4 Seals .....................................................................................................................................................................25
3.6.5 Nozzles and center jets ...............................................................................................................................27
3.6.6 Cutting structure components .................................................................................................................28
3.6.7 Steel Tooth Components .............................................................................................................................29
3.6.8 Compact shapes ..............................................................................................................................................29
3.7 KYMERA BITS ................................................................................................................................................... 31
3.7.1 Kymera Manufacturing ..............................................................................................................................31
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
2 Introduction
2.1 History
Drilling for oil and gas is getting more advanced and challenging. New technologies are exploring in order to
solve the most crucial technological problems in smart and cost efficient way. There are many parameters related
to operations that needs to be planned an evaluated and also modified in order to improve the drilling process.
Drill bit optimization is very important subject in drilling services. The bit is a major tool that has a big impact
on the whole drilling process. Bit selection is one of the important parameters for planning and designing new
wells. Choosing the wrong bit or damaging the bit in the formation can be of a big cost to an operator
companies. Bit selection is a hard task to perform. There are many aspects that need to be considered and
evaluated before decision is made. The operator companies are exploring oil and gas areas that were totally
impossible to drill for 30 years ago. The need for new bit designs and optimization of those is enormous.
Economical savings is one of the main drags for searching new and better solutions.
The first two –cone model bit had cones, which were unable to change. When the bit became worn out, the bit
was discarded. In 1917 the Hughes Company presented a cone, which was able to change when required. In
1933 was introduced the first Tricone bit as the type we know today. The bit was primary used for drilling
medium to harder formations.
In 1976, Christensen introduced the first Polycrystalline Diamond Compact bit, increasing the capability to drill
in softer formations. The market of the diamond bits has grown considerably. PDC are used in longer sections
where the seal and bearings of the Tricone bit cannot last long. Another factor that contributes to expanding PDC
market is the rig cost. Rig cost has increased significantly the last decade.
In 2010 the first hybrid bit was presented by Baker Hughes. This bit is unique of its type. It combines both the
PDC parts and Tricone parts. The Kymera marked has enormously increased the last few years. The bit proved
to be a future solution for challenging formation, such as highly interbedded formations, conglomerates and etc.
The main purpose of that document is the optimization and comparison between conventional bits such as PDCs
and roller cones with the new hybrid bit Kymera. It involves optimizing the drilling parameters. Increasing the
ROP and bit stability will be the major tasks that are going to be addressed.
The scope and objective of this report work contains theoretical, analytical and experimental studies. The
thesis contains the following information:
Presentation of the different types of bit manufactured by Baker Hughes
Theoretical models and calculations for MSE, DOC, UCS, bit stability, aggressiveness
Experimental test performance
Experimental test results
Results analyses and conclusions
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The drill bits are important tool in drilling services. There are three major types of bit that are used in the oil
business:
PDC
Tricone
Kymera
It is a new generation of old drag bit. PDC bit design is more durable. There are no bearings to wear out or
broken cones that may cause junk in hole.
The structure of the PDC bit can be broken down to three major parts:
Cutting structure,
Bit body
Shank.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
This part of the PDC structure can be either synthetic diamonds or natural industrial grade diamonds. The
cuttings type used depends on the formation to be cut and the application.
The PDC cutting structure can either consist of synthetic diamonds or natural industrial grade diamonds.
The diamond is the hardest material that we currently know of. Hardness is described as resistance to scratching
and it has a range of 1 (softest) and 10 (hardest). Diamond has the hardness of 10 on the Mohs scale of mineral
hardness. There are two mechanical properties that describe the diamond – hardness and toughness. Toughness
is the material ability to resist breakage from forced impact.
Industrial diamonds are valued mostly for their hardness and thermal conductivity. The use of diamonds in the
industries has been associated with their hardness. The diamonds are used in drill bits cutters especially because
of their impact resistance, ability to grind and cut any material.
Synthetic diamonds are diamonds that are produced in the laboratory. The majority of the available diamonds are
produced by so called High Pressure High Temperature process. Another popular method is chemical vapor
deposition (CVD). The growth occurs under low pressure (below the atmospheric pressure).
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
PDC cutters are formed from the synthetic diamond crystals (feedstock) and are loaded in a protective holder
assembly with a tungsten carbide substrate.
PDC cutters consist of many synthetic diamonds bonded to a cemented tungsten carbide. There are three major
parts of cutter design:
Diamond table
Diamond Carbide Interface
Edge Geometry
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The thickness of the diamond table is determined by the application and the diamond table properties. Optimized
diamond table properties influence both abrasion resistance and durability.
Thinner diamond table are less durable but maintain better cutting efficiency. When choosing thicker diamond
tables we will gain more durability, but the cutting efficiency will not be maintained very well.
(Baker Hughes (2013) – Bit Tech Training – Book)
Internal geometry has a very important role in cutter durability and impact resistance. Test studies have shown
then planar interface increases the residual stress between the diamond table and carbide substrate hence lower
durability and separation of the diamond table from the carbide substrate. The studies showed that non-planar
interface allows minimizing this effect of the residual stress.
Residual stress is simply the stress that is residing in the cutter after the cutter manufacturing process.(Baker
Hughes,(2008) – Diamond Tech – Student Guide)
Cutter back rate is the one feature that provides the aggressiveness of the bit. Larger back rake improve the
durability but decrease the aggressiveness.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Cutter chamfer is the feature of a diamond cutter that protects against forced impact. Larger chamfer improves
durability but decrease the aggressiveness. The chamfer is a small bevel at the edge of the diamond table.
Typical chamfer properties are height and angle of the chamfer. Diamond is a brittle material and crack is very
easy to be created and propagated. Reducing these sharp edges leads to high impact resistance. The choice of
chamfer on a certain bit is determined by the formation. Smaller chamfers require less force to be broken and
damaged. (Baker Hughes, (2008) – Diamond Tech – Student Guide)
A higher back rake will direct cutting edge forces into the substrate while a lower back rake will direct those
through the diamond table. Higher back rake also provides greater resistance to fracture but decrease the
efficiency. Smaller back rakes require smaller weight on bit in order to generate a given torque. (Baker Hughes,
(2008) – Diamond Tech – Student Guide)
Hughes Christensen Company patented polished cutters invention. Polished cutters proved to be more efficient
than the non-polished cutters. The polished surface decreases the friction between the cutter and the cuttings.
Polished cutters have improved the downhole cleaning issues and minimized the bit balling and bottom balling
problems. The cuttings are easily removed from the cutter surface and don’t create any additional thermal and
frictional issue to the bit. The surface finish of a conventional and polished cutter differs: (Patent, Baker Hughes
– Polished Cutters)
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The main purpose with the cutters is to shear the formation in efficient matter, which means use less energy
(WOB) per unit volume rock. The cutters needs to remain durable and impact resistant through the whole run.
Cutters have to provide the predicted ROP and DOC.
It is an important concept connected to the cutting mechanics. DOC is the distance that the cutter is intended into
the formation per revolution. (Baker Hughes,(2008) – Diamond Tech – Student Guide)
When the rate of penetration (ROP) and Revolutions per Minutes (RPM) are known, the DOC can be calculated
as follows:
DOC = ROP/RPM*5
¾ .inch (19mm)
5/8 inch (16mm)
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
½ .inch (13mm)
3/8.inch (8mm).
19 mm cutter generates the largest cuttings. The most usable diamond height 13mm has the most versatile cutter
size. 8 mm they provide design flexibility in small diameter bits. (Baker Hughes (2013) – Bit Tech Training –
Book)
This is the part of PDC bit that holds the cutting structure. This part is essential for bit profile, waterway, junk
slots, blades and gauge.
The part is made of hardened steel. The shank contains the identification slots and a bit breaker slot as well as
the API threaded connection that connects the bit with the drill string.
Polycrystalline diamond compact bit bodies are made of milled steel or tungsten carbide (matrix bit). The
current steel body bit consists of a crown and a shank. The crown starts as a piece of bar stock, which is a
piece of steel that requires the bit shape to be milled from scratch to form the bit crown. Cutter pockets
and other details are milled into the crown. The material for the bit body is a high alloy steel to obtain
good strength and thoughness.
Once the milling is complete the bit crown is welded to a shank at the same time as the cutters are brazed on to
the bit.
Steel is much less abrasion and erosion resistant than the tungsten carbide matrix. Therefore, a hardfacing
material is applied in critical areas in order to prolong bit body life. Typically, hardfacing is applied to the front
of the blades, in between the cutter pockets, behind the cutter pockets and on the gauge pads.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Profile – the certain shape of the bit when viewed from the side.The shape of the profile can be of significant
importance for bit performance. The objective of every profile is to provide balanced wear to the cutting
structure and optimize the bit stabilization.
This is one of the factors that are determining the number of the cutters that will fit on a blade. The longer the
length of the profile and the more cutters can be placed on the blades. The design of the profile is very essential
for determine bit balance and durability. A long profile will have more cutters, slower wear but less stable. A
shorter profile will have fewer cutters. It will wear more quickly, but will be more stable in directional control.
cone
nose
shoulder
3.3.2.1 Cone
The section of the profile between the centerline and the nose radius is called the cone. The cone provides
stabilization of the bit and helps it prevent from moving sideways. The cone provides some cutters redundancy
due to more surface area available to be set with cutters. (Baker Hughes (2013) – Bit Tech Training – Book)
3.3.2.2 Nose
This is the lowest point on the profile. The nose radius is the radius of the arc between the cone and the
shoulder/gage. The nose location is the distance from the centerline of the bit to the nose radius center point.
(Baker Hughes (2013) – Bit Tech Training – Book)
3.3.2.3 Shoulder
Shoulder area on the bit profile is the distance between the nose radius and the gage.
Short parabolic
Long parabolic
Shallow cone
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The bit density is a function of a blade count, profile length and cutter size. It can be classified as light, medium
or heavy and refers to the blade count.
There are two basic profile designs used for PDC bits, the shallow cone and parabolic profile.
Experience has proven the flat profiles are more stable. Parabolic profiles have two radii (nose and shoulder).
They are divided into three groups long, medium or short.
Long profiles are best suited for higher RPM ranges. The short parabolic profile is essentially provides the best
compromise of stability and cutter coverage. (Baker Hughes (2013) – Bit Tech Training – Book)
Blades need sufficient strength to withstand drilling stresses for the various applications. There are several blade
designs are used in PDC bits:
Pie-Shaped
Straight Blades – they allow for wider junk slots and better place for the nozzles
Curved Blades – they can inhibit effective cleaning and cooling of cutters on the shoulders
(Baker Hughes (2013) – Bit Tech Training – Book)
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
3.4 Hydraulics
This is a method that is used to control the flow of drilling fluid across the face of the bit. The scope of any
hydraulic design is to maximize the efficient drilling cuttings evacuation and provide cooling. Different
methods for hydraulic optimization designs are implemented.
Junk slots are the area between the blades of the bit that are used to evacuate cuttings into the annulus. Their
purpose is to carry formation cuttings away from the cutters. The number of the blades and the shank
diameter can limit the junk slots.
It is measured of the total cross-sectional area from each junk slot if the bit were viewed face-on, expressed in
square inches (in2). Larger junk slot area is used in soft formations with a higher penetration rate. When large
JSA is used it is easier to evacuate a large volume of cuttings away from the cutters and avoid bit balling. The
junk slot ratio is a ratio of a junk slot area to the total face area (hole area) of the bit. The junk slot is used to
compare different types of bit sizes and designs. (Baker Hughes, (2008) – Diamond Tech – Student Guide)
Face volume is a measurement for hydraulic capacity. The face volume considers the volume in between the
blades from the center of the bit and across the entire profile.
3.4.1.4 Gauge
Cutting removal
Cutter cooling
Cutting removal – this property is verified by through a simulator-balling test. Cutter cooling is the ability to
maintain a certain fluid velocity across the cutter face to cool the cutter during drilling. (Baker Hughes, (2008) –
Diamond Tech – Student Guide)
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The PDC bit can be exposed to one or more failure modes: fracture, wear and delamination.
3.5.1 Fracture
Cutter fracture comes as a result of an impact loads due to vibration and has two sub-categories:
chipping
spalling
3.5.2 Chipping
Chipping is a result from impact loads in the direction of cut, essentially parallel to the borehole bottom. The
vibration that cause the impact loads is usually lateral or stick-slip. This is the most often seen PDC failure.
(Baker Hughes, (2008) – Diamond Tech – Student Guide)
3.5.3 Spalling
Spalling, is caused by high axial impact loads. It represented by the separation of a partial thickness of the total
diamond layer from the face of the substrate
3.5.4 Wear
Hard and abrasive formations will cause wear on the cutters. Due to long and continuous rotating despite that the
diamond is very hard material, it is often seen wear on the cutters when the bit is pulled out of the hole.
Hard but not abrasive formations often cause heat checking on the cutters. Heat checking occurs when the cutter
substrate is rubbed against the formation. It is not that often seen failure compared to some other failures. (Baker
Hughes,(2008) – Diamond Tech – Student Guide)
This is the failure which will harm less the drilling process due to its low impact on the penetration rate. The
diamond lip is a slight and smooth wear with little or no fracture of the cutter.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
3.5.7 Delamination
Delamination is very rare seen in the new diamond cutters. This is identified as a separation of the diamond table
and the tungsten carbide substrate. This is a quite serious failure which can cause low Rate of Penetration and
high torque. (Baker Hughes, (2008) – Diamond Tech – Student Guide)
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
This is the part of the Tricone body that holds the cone, bearings, seals and the nozzles. It is steel body that is
milled and machine. The three legs are welded afterwards and hold the most of the weight of the bit.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
As mentioned earlier it the thesis the first generation Tricone bits were the two cone bits. It was Howards
Hughes, Jr who invented it in 1909. The technology behind this type of roller cone was revolutionizing. It was
not only scraping the rock but the hard rock was powdered. This allowed the drillers to drill faster and deeper.
In 1925 new Acme self-cleaning cones were introduced. These new solutions manage to double the
penetration rate and increased the footage with 80 %. (Tricone Technologies, Student Guide, Baker Hughes
(2008)
8 years later Tricone bit was introduced to the drilling operators. The bit ran smoother and longer. In 1951
Hughes introduced the first Tungsten Carbide Insert (TCI). These are specially designed for harder
and challenging formations.
The bit technology has improved a lot the last decades. The bearings and seals has been improved and new
technologies are implemeted. Seal lifetime is significantly increased. Tricones can drill longer and advanced
well paths. Steel tooth and TCI are still leading technology in shorter sections where boulders and other hard
rocks are present. (Tricone Technologies, Student Guide, Baker Hughes (2008)
Steel tooth cones are machined from forgings of an alloy steel. The cones are milled to form the shape of the
steel tooth. The shape of the actual teeth will depend on the purpose of the bit. To protect the steel tooth,
hardfacing is welded on the cutting structure. The hardfacing contains of tungsten carbide particles designed to
maximize the cutting life of a tooth. The shape and density of the teeth depends on the formation application.
Larger teeth with bigger space between are much suitable for soft to medium formations. Large teeth can grab
and crush bigger volume of rock, thus drilling faster.
Smaller teeth with small space between are designed for medium to harder formation. Harder formation drilles
slowly with low ROP and RPM. In order to drill this fomation the bit has to be able to carry a high weight on bit
and resist to damage. Thats is the main reason small teeth are applied. They are able to grind the formation
slowly with high weight on bit.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The main difference between these two bits is that the teeth in Tungsten Carbide Insert (TCI) bits are pressed
into the cones and not milled into them. The insert teeth are milled and machined and then mount on the cones.
The amazing thing here about this type of bit technology is that the only force that holds the tungsten carbide
inserts pressed in the bit cone, is the friction between the insert and the body.
The size and type of the components in the bit depends on the formation hardness. Bits for soft formation require
smaller weight, smaller bearings, smaller cone shell thickness and thinner legs. That gives more room for long,
thin cutters. Drilling in hard formations requires weight, bigger bearings, steadier body and stubbier cutters.
The roller cone bits consist of different types of bearings. TCI are the drilling solution for hard and challenging
formations.
3.6.3 Bearings
The two main types of rock bit bearings are journal bearings and roller bearings. Both types of bearings are
designed to carry large radial loading:
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Journal bearings (« friction bearings») have high load capacity due to their large load area. These types of
bearings are space efficient and that make them especially used in small bit sizes. Journal bearings have RPM
limitations due to friction. (Tricone Technologies, Student Guide, Baker Hughes, 2008)
Advantages:
Disadvantages:
RPM limitations
Runs “ Hot”
Temperature is not an issue for roller bearings since they are anti-frictional bearings. Compared to journal
bearings, roller bearings need more space in the cone of the bit. This is the main reason that these types of
bearings are used in rock bits of larger sizes. Roller bearings are weight limited due to rolles impose line loading
on the roller races.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Advantages
Disadvantages
3.6.4 Seals
There different types of seal systems that are used in the different bit sizes. There is O-Ring seals and Metal Face
Seals. The seal function is to separate the internal greased bearing from the drilling mud.
Figure 22 The seal function is to separate the cone grease from the oil
The O-ring is held under compression between polished surfaces between the head and the cone. The seal helps
to isolate the greased section from the drilling mud system.
Single Energizer Metal (SEM) seal system has fewer sealing components and silver plated insert:
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Metal face seal consist of elastomer that is used to “energize” metal seal surfaces.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Grease Mud
Head
Energize
r
Sph
eric
Figureal27 Dual Metal Face Seal System
radi
us
The Metal Face Seal comprises polished metal rings retained by static elastomer ‘energisers’. A dynamic seal is
created across the highly wear resistant metal faces. The advantages with this seal system are that it has high
RPM potential, high temperature capacity, and obtain longer life. (Tricone Technologies, Student Guide, Baker
Hughes (2008))
Nozzles are manufactured of Tungsten carbide material. Their main function is to provide sufficient cleaning and
cooling to the bit in order to avoid downhole bit problems. Nozzles size and position are determined by the bit
formation application. The orientation of the nozzles streaming direction is computed and modeled in order to
assure best cleaning and cooling effect of the bit.
In certain applications a center jet is mounted in the center of the bit body. This feature is specially used when
extra efficient cleaning is needed. The subject features is a hydraulic optimized feature in order to assure better
cleaning and cooling of the bit.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
In this section the main components of the cutting structure will be presented. On the Fig.30 below are shown
the different components of the cutting structure. As can see there are certain differences between the
components of the Steel Tooth bit and TCI bit.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Different formation applications require different type of cutting structure. In soft formation high projection
tooth structure is used with long crest. The cutting structure is with bigger teeth and wide space. Medium
projections and short crest are usually used in medium formations. In soft formations rock failure can be easily
achieved by long steel tooth. The teeth can easy grab and crush the formation in more efficient way. In soft
formations usually balling is very often seen issue. When using a bit with long teeth, balling potential will be
minimize and avoid.
On the other side when drilling through hard formations TCI bits are usually applied. Due to their durability,
stability and wear resistance those bits are the most preferred ones when drilling in challenging formations.
Small, wear resistance tungsten carbide cutters help to grind the hard formation and mill it carefully.
There are four main compact shapes that are used according to the application requirements.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The body is made of steel. The steel body is machined. Then the shank is attached and welded to the PDC body.
The next step is to apply the hardfacing. The cutters are brazed and grind afterwards.The cone is attached onto
the head. And finally place the PDC body into assembly fixture with shank down. Both the head/cone body
should be positioned into the correct pockets. Last weld the all the parts, add the grease in order to provide
lubrication and decrease the frictions in the cone rotation.
Both elastomer seals and Metal Face Seals are available for Kymera. For elastomer seals the most commonly
used are High Aspect Ratio seal (HAR). For metal faced seals (SEMII).For Kymera as for the other roller cones
bit, the type of seal that is going to be used depends on the space possibility in the cones.
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
3.7.2.2 Inserts:
On the roller cone cutting structure inserts that are used in Kymera designs are chisel and conic. Ovoid inserts
are used in the heel row. There are no steel teeth that are dressed on Kymera. The bit is designed to be durable
and impact resistant.
The PDC cutters that are mounted on the Kymera blade have the same manufacture technology as for the PDC
bits. Kymera always is dressed with the last diamond technology cutters. The density and size of the cutters
depends on the number of PDC blades that on a particular hybrid design. The space availability of the blade
limits the cutter variety.
3.7.2.4 Nozzles:
The choice of nozzles is quite depending on the size of the bit and its formation application Small bit sizes has as
well space limitations. There are different size of nozzles which can be dressed on a Kymera in order to achieve
the required horse power for sufficient hole cleaning and bit cooling.
The range of application of the hybrid bit technology continues to expand into more complex drilling well
profiles. Overall Kymera has shown increased efficiency in applications were conventional bit struggle to
achieve any progress at all. Despite its short history (only 4 years), the hybrid bit has already proven its value
and contribution in challenging formations. Kymera is highly recommended for applications as:
- Interbedded formations
- Nodular formations
- Directional applications
- Stick slip problems
- Large diameter bits
- Poor hydraulics
32
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Drillers can use the model in order to evaluate the efficiency of the drilling parameters. MSE can be used under
well planning phase in order to adjust the parameters. R.Teale introduced this formula in 1964. MSE is defined
as the amount of energy required to remove 1cm3 of rock. Teale then performed lab test that demonstrated the
energy per volume of rock destroyed to be relatively constant, regardless in ROP, WOB and RPM.
Teale also observed that the value of MSE was approximately equal to the compressive strength of the rock. The
tests that he conducted were done under atmospheric conditions where the rock failed in a highly efficient, brittle
failure mode. In field conditions the peak bit efficiency are usually much lower, often in the 30-40% range. For
operational reasons MSE was adjusted so that the value would be closer to the known rock strength. The EFFm
that the operators are using them is 0.35:
When the bit is operating at its peak efficiency, the ratio of energy to rock volume will remain relatively
constant. When varying the different drilling parameters such as weigh on bit (WOB) and rotary speed (RPM)
we can evaluate the bit efficiency. If despite the increasing of WOB the MSE stays constant one can still assume
that the bit is drilling efficiently. If the MSE increases significantly, the bit has foundered. Then the parameters
need to be adjusted accordingly in order to minimize the MSE again. MSE equation is expressed as follows:
(Dupriest, Fred E., ExxonMobil Corp. Witt, Joseph William, Remmert, Stephen Mathew, ExxonMobil Qatar –
Maximizing ROP with Real-Time Analysis of Digital Data and MSE)
33
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Compared to roller cones, PDC bits have high aggressiveness. PDC shear the formation and they cause a higher
torque. The cones on the tricone bits are freely rotating and hammer away the formation. The torque generated
by the tricones is less than that of the diamond bits.
Aggressiveness and wear resistance are fundamental properties that need to evaluate for the specific application
where the bit is going to be applied.
The aggressiveness of a bit is determined as mentioned earlier in the thesis by the depth of cut the bit is designed
to remove. In roller cone bits the aggressiveness is determined by the projection, pitch of the teeth and cone
offset. For the PDC bits the aggressiveness is determined by cutters exposure and cutter angle (Backrake)
Bit wear resistance is on the other hand determined by the cutter density of the cutters.
For roller cone bits in order to improve the wear resistance one have to add more cutter on the gauge, more
durable shapes of cutters. Applying diamond on the gauge cutter could be another solution to increase resistance.
Making the cutters more brittle and increasing the number of carbide inserts.
PDC wear resistance can be improved by increasing the length of the gauge so that more cutters can be placed on
and near the gauge and as well as the roller cones increase the carbide and the diamond content. The features that
make the bit more resistant at the same time make it more susceptible to cutter breakage. (Spaar, J.R.,
Ledgerwood, L.W., Hughes Christensen, Goodman, R.L. Graff, Moo, T.J., Chevron Petroleum Technlogy Co. –
Formation Compressive Strenght Estimates for Predicting Drillability and PDC Bit Selection)
The aggressiveness of the bit can be calculated by the following formula: (Pessier and Fear 1992)
Specific coefficient of sliding expressed a torque as a function of the WOB. This coefficient will be further used
to derive the mechanical specific energy. (Pessier and Fear 1992).
Higher Mu means that the bit can generate more torque with lower weight on bit but it can suffer from impact
damage in abrasive formations. “Mu” is determined as a measurement for bit aggressiveness.
Up until 1980s it was not that obvious that bit stability could be of a big issue. Thermal stability of the cutters
triggered many researches and lab testing through the years.
Bit Performance depends on BHA Performance. Drill collars tend to vibrate when rotated. BHA design and
operation controls the severity of this vibration. The resulting BHA vibration loads the bit unevenly. Bits that are
“stable” in the laboratory can become unstable because of these effects.
Bit stability is the ability of the bit to resist to drilling vibrations. There are different types of drilling vibrations
that cause inefficient drilling and bit damage impact. I am going to explain shortly the main types of vibrations.
Drilling vibrations sometimes can be easily detected by string movement, twisting, and irregular rotation. But
sometimes it is undetected by the drilling team and thus can cause a lot of damages.
34
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
When the string is moving up and down it creates forces that can damage the string and the bit. The bit
movement initiated by axial vibrations is called bit bounce. Bit bounce damages the cutters and bearings. These
type of vibrations can be detected from surface and can be mitigated.
(http://www.slb.com/~/media/Files/drilling/brochures/drilling_opt/drillstring_vib_br.pdf)
Torsional vibration can cause irregular downhole rotation. Stick-slip is one type of torsional vibration which
very common for PDC bit. The rotation of the bit becomes stationary and then followed by sudden quick
rotation. As the downhole conditions get more and more severe the stick slip can increase more. the stick slip
can lead to drill string buckling, bit cutter damage, BHA faulire due to high vibration level etc. These vibrations
are easy to detect by the downhole drilling data.
(http://www.slb.com/~/media/Files/drilling/brochures/drilling_opt/drillstring_vib_br.pdf)
Lateral vibrations are the type that can cause severe damage on the BHA and the bit. Whirl is the most severe
form of vibration. The whirl can create a bending moment that can result to connection fatique.
(http://www.slb.com/~/media/Files/drilling/brochures/drilling_opt/drillstring_vib_br.pdf)
Bit stability is basically the bit interaction with the formation. There are two factors that prompt bit instability,
they are the profile shape and the cutting structure. The main purpose is to find the profile that will minimize the
bit stability and increase bit durability at the same time. There are different methods and feature that can be
applied for that matter.
35
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Compressive strength and the drillability have been linked and observed in the laboratory and in the field for
many years. Rock strength is found to correlate well with overall measurements with the bit drillability.
The compressive strength is qualified as a function of confinement stress. With Mohr`s failure technique, it is
very important to understand that inherent rock strength properties (cohesion and angle of internal friction) must
be known before compressive strength can be calculated. The unconfined compressive strength is defined as the
load per unit area at which cylindrical specimen of standard dimension of soil fails in a simple compression test.
(Rao and Ranjan, “Basic and Applied Soil Mechanics”
In order to determine the compress strength we need to be supplied with shear sonic real time data. The strength
of the rock is very important value in bit selection and evaluation. The UCS is measured in psi. High values of
UCS are the most critical challenges in well objectives. Hard rocks can severly damage most of the bit types and
cause well instability and hole cleaning issues. High compressive strength can uncover any hidden harmful
formation rocks.
In order to evaluate if a certain bit has achieved the efficiency that was predicted in the prognosis, MSE and
UCS correlation can be plotted. It will show drill bit efficiency at the various drilling parameters that were
applied at the certain formation strengths.
36
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Test request is filled out through the LabQ. That is laboratory database software. The input information is listed
below:
Type of test, rock used, work description and other pertinent information filled out
Multiple tests require their own test request to be filled out
Tests are then scheduled by priority, urgency, rock availability and bit availability
When test is completed the data and photos are compiled and stored on the server
37
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Surface Rig, also known as Atmospheric Pressure Rig is located in the Drilling Technology Laboratory. The
Baker Hughes Drilling Technology Laboratory, located at The Woodlands Technology Center in The
Woodlands, TX, is the world`s premiere bit and cutter testing facility. The Laboratory is equipped with Bottom
Hole Simulator, the Visual Single Point Cutter, the Atmospheric Surface Rig and Boring Mills.
.
Alabama Marble was the first rock that was drilled. It is a marble that is found in a belt running to Talladega
County, Alabama. It is famous with its pure white color and its crystalline structure. Alabama marble is
considered as one of the finest stone.
It is metamorphic rock that derives from limestone (sedimentary rock). It is subjected to high heat and thus has
changed its structure. Alabama marble is more durable than the limestone. The marble is as well very fine
grained. (http://www.encyclopediaofalabama.org/face/Article.jsp?id=h-2047)
Alabama Marble can be white, grey, pink, red and black depending on the impurities in the original limestone
and dolomite.(http://archives.alabama.gov/emblems/st_rock.html).
Alabama Marble was chosen for the experimental test. The reason for that is the high rock strength of the rock
and its properties are close to the properties of rocks which are very challenging to drill in the Norwegian
Continental Shelf. There were many bit failures while drilling in hard limestone in Norway. This issue is the
main reason for conducting these tests.
On the table below are described the rock properties of the subject Alabama Marble.
38
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Stability
Efficiency
Performance
39
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
On this page is possible search for bit tests by bit size, bit type, rock type, test type, etc. The test that have been
performed before are stored for future references and guidelines. This search gives the option to compared tests
with different bits.
40
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The picture above shows basically typical test that is conducted in the surface rig. It is shown the rock bit that is
drilled. On the right side it is easy to see the control room where the operator is monitoring and controlling the
drilling unit. Over the rock, there is hydraulic pipe. The drill bit is mounted on it.
The surface rig is also equipped with camera. The real time camera makes it possible for engineers, operators in
Baker Hughes to see and follow up the test remotely. It is possible to take screen shot of a real time camera.
Most of the screen shots are saved in internal database archive for future references.
41
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
42
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
While performing the tests the entire process is documented with pictures. These kinds of documentations are
quite important under drill bit evaluation. Fig. 37 is an example of typical experimental pictures taken. Damages
and impacts can be revealed and studied. Drill bit failures can be avoided and new optimization techniques could
be implemented.
This chapter will present the results of the test in two stages. I will then discuss the influence of the drilling
parameters and variables on the rate of penetration, stability and efficiency of the certain bit.
Three different technology bits will be tested. For that purpose we have chosen TCI, PDC and Kymera bit. For
more detailed see the table attached below:
In this laboratory test two matrixes were chosen. Both of them covered common parameters along with
considered operating range of the testing equipment. The formation was the same in both stages. The tests were
conducted in Alabama Marble rock.
Different drilling parameters were applied at the both stages and stability and efficiency will be evaluated at the
different scenarios.
The stability test was conducted in Alabama Marble at 60 ft/hr ROP, in RPM controlled with six different RPM
steps. The ROP is a result of the applied WOB. The formation is the same this allows to keep the WOB constant.
For each RPM/ROP step the weight on bit applied was respectively (rage from 0 to 40 000lbs). The drilling data
was recorded throughout the test
The second stage of the test was executed as well in the Alabama Marble with the following parameter:
43
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
The high RPM test was conducted to observe how the bit behavior is influenced by different values of rpm. It
will be evaluated bit stability and efficiency at the different rpms. In order for a bit to be considered as stable, all
the energy that is applied by the RPM need to be transferred in higher values of ROP.
44
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
45
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Figure 51 9.5 inch Kymera photos after the test was conducted
46
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
47
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Figure 54 9.5 inch PDC photos after the test was conducted
48
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Figure 57 9.5 inch TCI Photos after the test has been conducted
49
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
In order to evaluate the bit aggressiveness, a test with constant ROP of 60 ft/hr and in steps increasing RPM was
conducted. The three bits were tested in the same Alabama Marble rock.
Mu vs RPM
0.8
0.7
0.6
0.5
Mu
QT406FX
0.4
KM623
0.3
VMD-20
0.2
0.1
0
0 50 100 150 200 250
RPM
From Fig. 55 it is observed that the PDC bit has the highest aggressiveness value, as expected. Although
aggressiveness is good property, here it is important to remark that PDC bit aggressiveness is very much
uncontrolled. The Mu value can vary from 0.5 to 0.8 for the same ROP and RPM values. This type of behavior
could be quite disastrous in the field. A bit with uncontrolled aggressiveness could generate uncontrolled torque
and hence uncontrolled ROP. Uncontrolled ROP could lead to hole cleaning and pack off issues which in the
other hand can jeopardize the drilling section.
I can further elaborate that Kymera has shown stable and controlled aggressiveness. Another phenomena that is
observed as well is that with increasing RPM at constant ROP, at certain WOB values, the Mu values for
Kymera and Tricone are declining. Hence the drilling efficiency will be reduced respectively.
Drilling efficiency is very important parameter that needs to be discussed. From Fig. 56 I have plotted the test
results for efficient energy and how this energy varies with increasing RPM, at constant ROP of 60 ft/hr. The
specific energy needs to be around the same value as the UCS of the Alabama Marble rock that was drilled. The
rock in this case has 15 ksi UCS. From this graph I can see that the PDC and Kymera are most efficient when
spinning from 75 to 150 rpm. For RPM higher than those values the efficiency of the bits starts to vary a lot.
50
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
MSE vs RPM
60000
50000
Specific Energy (psi)
40000
30000 QT406FX
KM623
20000 VMD-20
10000
0
0 50 100 150 200 250
RPM
Fig 61 shows the magnitude of vibrations that all three bits encountered at increasing RPM and constant ROP.
It is desired to have a whirl traction value under 0.10 for all ranges of RPM. When the whirl traction remains
under 0.10, the bit is thought to be stable. All of these bits show to be stable. The PDC bit shows lowest level of
whirl at 50 to 150 rpm. After increasing the RPM further than 150, PDC shows increasing of vibration level.
Kymera on the other hand shows more stable drilling vibration level. It starts with 0.4 to 0.6 whirl traction at 50
rpm and declines to 0.2 at 250 rpm. Tricone shows also generally low whirl traction below 0.1 but the vibration
levels variations are bigger. Tricone has declining vibration level as well as the Kymera, which is expected due
to roller cone technology on both of the bits.
51
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
0.07
0.06 QT406FX
0.05 KM623
0.04 VMD-20
0.03
0.02
0.01
0
0 50 100 150 200 250
RPM
The next Fig.62 shows how the aggressiveness of the bit influence the torque generated by each of the bit. PDC
are expected to generate more torque because they are more aggressive (Mu). Tricone require more weight to
produce a given ROP than PDCs and Kymeras. Higher slopes (Torque vs WOB) indicate higher aggressiveness
(μ). On this figure as well we can see the same pattern that we discussed earlier. The PDC bit is more aggressive
but as well not controlled aggressive. The Torque fluctuations are higher and hence the ROP variations are
expected to be bigger. This feature again needs to be considered when applying PDC bit in this type of
formation. Not only the ROP could be jeopardize but bit integrity as well.
52
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Torque vs RPM
2500
2000
1500
Torque
QT406FX
KM623
1000
VMD-20
500
0
0 50 100 150 200 250
RPM
Aggressiveness of the bits versus the depth of cut is ploted on Fig.63 below. This shows that the PDC is by far
the most aggressive bit. The Kymera is in between like expected and the Tricone has the lowest aggressiveness.
It is obvious that in the range 0.15 of depth of cut and higher (which represents softer formation), the bit
aggressiveness is well controlled. All the bits show constant increasing slope. When looking further on the range
below 0.15 DOC, respectively harder formations, PDC shows higher but unstable and scattered aggressiveness
values. Kymera shows higher and stable values compared to tricone hence Kymera will deliver higher ROP and
stable efficient drilling.
Each bit type torque decreases as the RPM increases because the bit is taking a smaller bite of the formation.
DOC is calculated by ROP/ 5*RPM which would mean the higher the RPM the smaller the DOC. Since the bits
are not removing as much rock they are not generating as much torque.
53
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Mu vs DOC
0.8
0.7
0.6
0.5
Mu
QT406FX
0.4
KM623
0.3
VMD-20
0.2
0.1
0
0 0.05 0.1 0.15 0.2
Depth Of Cut (in/rev)
Fig.64 shows drilling efficiency of the three bits versus the depth of cut. The specific energy needs to be around
the 15 ksi which is the UC strength of the rock. For the same ROP, WOB and increasing RPM the bits perform
differently in the same formation. Tricone shows to be more efficient when DOC is lower than 0.15 which
reperesents hard formation. This pattern is expected, tricones are by far the most efficient bits in hard formations.
Further studying on the Kymera performance we can see that hybrid bit shows as well good efficiency in hard
formation. While in higher DOC values we can see that PDC efficiency is increasing. But still Kymera and
Tricone shows better and more sufficient drilling performance in this formation.
54
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
80000
70000
60000
50000
MSE
QT406FX
40000
KM623
30000 VMD-20
20000
10000
0
0 0.05 0.1 0.15 0.2
Depth Of Cut (in/rev)
By looking at the results on Fig. 65 it is easily seen why the PDC bit is inefficient at DOC lower than 0.15. By
plotting the vibration level versus depth of cut at constant ROP and increasing RPM, it is obvious that when
encountering harder formation PDC bit experiences higher vibration level. The energy transferred to the system
by RPM is lost in vibration and less energy in transformed in ROP. Kymera shows low vibrational level over all
with small fluctuations. Tricones appears to be overall stable with whirl traction level lower than 0.1, but as the
PDC, Tricone also shows higher vibration fluctuations which can cause bit instability on bottom.
55
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
0.07
0.06 QT406FX
0.05 KM623
0.04 VMD-20
0.03
0.02
0.01
0
0 0.05 0.1 0.15 0.2
Depth Of Cut (in/rev)
In order to see torque behavior of the bits with constant ROP and increasing RPM versus the depth of cut
prorogated in the formation, I will have look at Fig.66. As expected from the prevous figure which represented
the vibration level, I observe here the same phenomenon. The torque for PDC bit is quite scattered for harder
formation. It means that the bit generated higher and uncontrolled torque fluctuations. Kymera and Tricone here
should be mentioned that they deliver more stable control torque. Smaller DOC means that the bit is taking
smaller volume of the formation per revolution hence generating lower torque as well.
56
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Torque vs DOC
2500
2000
1500
Torque
QT406FX
KM623
1000
VMD-20
500
0
0 0.05 0.1 0.15 0.2
Depth Of Cut (in/rev)
From Fig.67 below we can conclude that while operating with low RPM and WOB the three bits delivere
unstable and uncontrolled ROP. That behavior is expected since the bits need higher RPM to mitigate the
generated vibration levels. As the WOB was increased at 20000 lbs as shown on the Fig. 68 and the RPM was
respectively increased the bits appeared to deliver more stable and controlled ROP. Kymera and Tricone
managed to keep almost constant ROP throughout the rest of the run. The PDC on the other hand delivered more
fluctuating ROP, varying from 30 to 60 ft/hr.
57
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
ROP vs Torque
180
160
140
120
ROP (ft/hr)
100
QT406FX
80 KM623
60 VMD-20
40
20
0
0 500 1000 1500 2000 2500
Torque
PDC are expected to generate more torque because they are more aggressive (Mu). Tricone require more weight
to produce a given ROP than PDCs and Kymeras. When drilling with Kymeras that is one thing that has to be
considered about the drilling system on whether it is stiff enough to provide the extra weight needed to the
Kymera or Tricone. Higher slopes (Torque vs WOB) indicate higher aggressiveness (μ).
58
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Torque vs WOB
2500
2000
1500
Torque
QT406FX
KM623
1000
VMD-20
500
0
0 10000 20000 30000 40000
Weight On Bit (lbs)
There have been done a lot of experimental work on this subject. Langeveld described that with increasing RPM
bit has greater tendency to whirl. (Langeveld, 1992).
The main purpose of this test was to follow the development of the bit stability at constant low RPM (80rpm)
and constant high RPM (200rpm) in Alabama Marble.
From Fig.69 shows that PDC is most aggressive of all the bits. It has Mu value of 0.6 at the beginning of the test
from 0-60 ft/hr. With increasing ROP and WOB, but constant RPM the aggressiveness of the bit start to decline
and gets equal to the aggressiveness of the Kymera at 180 ft/hr. This behavior is expected since PDC bits need
less WOB compared to Kymera and Tricone.
Tricone and Kymera on the other hand show lower Mu values but inclining behavior. Kymera increased the Mu
values from 0.3 to 0.45 with constant RPM of 80.
59
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
0.7
0.6
0.5
QT406FX
Mu
0.4
KM623
0.3
VMD-20
0.2
0.1
0
0 30 60 90 120 150 180
ROP (ft/hr)
The second test was conducted with 200rpm for the same ROP values as the first one. Diamond bit shows quite
high and unstable Mu values, which varies from 0.45 to 0.75. Kymera shows lower aggressiveness but much
more controlled and stable throughout the whole run. Tricone shows much lower and stable aggressiveness and
Mu values of 0.1 to 0.15.
60
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
0.7
0.6
0.5
Mu
0.4 QT406FX
KM623
0.3
VMD-20
0.2
0.1
0
0 30 60 90 120 150 180
ROP (ft/hr)
In order to look into the drilling efficiency of the bits we correlated MSE values to the ROP at constant RPM of
80. See Fig.71 below, describes clearly that at this RPM and 15ksi USC of the rock, Kymera and Tricone are the
most efficient of all tested bits. With increasing the WOB and the ROP, the efficiency of these two bits is even
improving.
30000
Specific Energy (psi)
25000
20000
QT406FX
15000 KM623
VMD-20
10000
5000
0
0 30 60 90 120 150 180
ROP (ft/hr)
61
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Fig.72 shows how the efficiency of the bits has changed after RPM has been increased to 200 rpm. Kymera that
was most efficient at 200rpm now have changed place with Tricone. Roller cone bit seems to be the one that
delivered the most efficient drilling at 200 rpm. But overall the bits delivered more unstable and uncontrolled
drilling efficiency compared to 80 rpm. With increasing ROP Tricone and Kymera shows significant efficiency
improvement.
90000
80000
70000
Specific Energy (psi)
60000
50000 QT406FX
40000 KM623
VMD-20
30000
20000
10000
0
0 30 60 90 120 150 180
ROP (ft/hr)
Next step is to discuss how the bit stability is influenced by the constant low and constant high RPM. Fig. 73
below presents the vibration level suffered by each bit at different values of ROP and WOB. Fig.74 shows the
same phenomenon but with constant RPM of 200. By comparing the two figures I can first conclude that while
drilling with lower RPM all the three bits experienced higher whir traction but with more stable and controlled
drilling. When drilling with 200rpm the bits whirl traction is much lower but more unstable and fluctuating this
causes bit damage and failure. PDC bit shows to induce less whirl vibration while drilling with 80 rpm. Kymera
on the other hand proved to be more stable and induce less vibration when drilling with 200rpm nad ROP up to
130 ft/hr. Kymera aslo showed unstable vibration level when drilling with ROP higher than 130 ft/h.
62
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
0.25
0.2
Whirl Traction
0.15
QT406FX
KM623
0.1
VMD-20
0.05
0
0 30 60 90 120 150 180
ROP (ft/hr)
0.12
0.1
Whirl Traction
0.08
QT406FX
0.06 KM623
VMD-20
0.04
0.02
0
0 30 60 90 120 150 180
ROP (ft/hr)
Fig. 74 and Fig 75 are representing the torque results from drilling with constant RPM of 80 and 200 rpm. As
expected the PDC bit generates more torque due to their aggressiveness. They create a high torque slope. While
63
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
Kymera and Tricone need more weight on bit to generate more torque. When spinning with 200 rpm it is shown
that all the three bits generated lower torque compared to the one generated with 80 rpm. This is explainable
with the depth of cut being smaller when spinning with higher RPM, hence lower torque generated.
5000
4000
Torque
3000 QT406FX
KM623
2000 VMD-20
1000
0
0 30 60 90 120 150 180
ROP (ft/hr)
2500
2000
Torque
1500 QT406FX
KM623
1000 VMD-20
500
0
0 30 60 90 120 150 180
ROP (ft/hr)
64
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
3.10.7 Conclusion
The experimental test conducted proven to be very knowledgeable. They showed that overall the bit drilling
technology is performing as expected in the subject formation. Alabama Marble is hard formation that generates
challenging drilling process for most of the bits that will be applied.
All the three bits show good response and efficiency in this hard formation. Things that need to be considered
when choosing the right bit for the next formation with the same hardness, is that PDC bits deliver high ROP and
high torque values. They are generally good for long sections, but they tend to generated more unstable drilling
and uncontrolled ROP in this subject formation. This behavior can cause potential cutting structure damage and
failure. PDC bits are perfectly suitable for softer formation (higher than 0.15 DOC). There they can deliver
extreme ROP and good stable drilling.
TCI proved to deliver good and stable drilling in Alabama Marble formation. They are perfectly suited for that
kind of formation. They don not deliver the highest ROP but they have the best durability properties from of all
the bits. TCI showed very good response and efficiency at DOC below 0.15 which means harder formations,
while in softer they showed to tend to be more unstable and deliver lower ROP. If formation is represented of
hard rocks, TCI is the best solution for those types of applications.
Kymera has proven to be the key drilling tool for formations with varying hardness. It has shown that it can
deliver the same or better ROP efficiency and stability in harder formations as the TCI bits. At the same time can
drill efficiently softer formations without jeopardizing the ROP and stability as the PDC bits.
65
Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
References
1. Baker Hughes (2013) Hughes Christensen – Drill Bit Catalog
8. Bilgesu, H.I.SPE; AL-Rashidi, Aminian, K., SPE, Ameri, S., SPE, West Virginia University (2008)– A
new approach for drill bit selection
9. Dolezal, Tisha, Felderhoff, Floy Holliday Alan, Baker Hughes, Chesapeake, Greg Bruton, (2011) –
Expansion of field testing and application of new hybrid drill bit
10. Dupriest, Fred E., ExxonMobil Corp. Witt, Joseph William, Remmert, Stephen Mathew, ExxonMobil
Qatar – Maximizing ROP with Real-Time Analysis of Digital Data and MSE
11. Spaar, J.R., Ledgerwood, L.W., Hughes Christensen, Goodman, R.L. Graff, Moo, T.J., Chevron
Petroleum Technlogy Co. – Formation Compressive Strenght Estimates for Perdicting Drillability and
PDC Bit Selection
12. Ernst, Stephen, Pastusek, Paul, Lutes Paul, Hughes Christensen (2007) – Effects of RPM and ROP on
PDC Bit Steerability.
13. Pessier, R.C, Hughes Tool Co.,Fear, M.J., BP Exploration (1992) Quantifying Common Drilling
Problems with Mechanical Spesific Energy and a Bit- Specific Coefficient of Sliding Friction
15. http://www.slb.com/~/media/Files/drilling/brochures/drilling_opt/drillstring_vib_br.pdf
16. McPherson, Alan – State Geosymbols: Geological Symbols of the 50 United States
17. Fuselier, Danielle M., Vempati, Chaitanya R.; Oldham, Jack; Patel, Suresh G., Baker Hughes
Inc.(2010) – Understanding the Contribution of the Primary Stability to Build Aggressive and Efficient
PDC Bits
19. Mensa – Wilmot, Graham,;GeoDiamond, Fear, Martin J- BP – The Effects of Formation Hardness,
Abrasiveness, Heterogeinity and Hole Size on PDC Bit Performance
20. Jain, Jayesg R.; Oueslati, Hatem; Hohl, Andreas, Reckmann, Hanno; Ledgerwood III, L.W.;SPE, Baker
Hughes Incoroporated, Tergeist, Mathias, Prof. Dr-Ing habil. Ostermeyer, Technische Universitat
Brauschweig – High-Frequency Torsional Dynamics of Drilling Systems: An Analysis of the Bit-
System Interaction
21. Black, Alan D., SPE, TerraTek, Bland, Ronald G.SPE, Baker Hughes, Curry, David A., SPE,
Ledgewood III, L.W., SPE, Hughes Christensen, Robertson, Homer A.,SPE, Judzis, Arnis, SPE,
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Drilling efficiency and stability comparison between Kymera, Tricone and PDC bits
TerraTek, Prasad, Umesh; SPE, Hughes Christensen, Grant, Timothy, U.S. Department of Energy –
Optimizations of Deep Drilling Performance With Improvements in Drill Bit and Drilling Fluid Design
22. Smith, R.H., Hughes Christensen, Lund, J.B., Hughes Christensen, Anderson, M., Hughes Christensen,
Bexter, R., Enron Oil & Gas Co. – Drilling Plastic Formations Using Highly Polished PDC Cutters.
23. Scott, Dan Eugene, Baker Hughes Inc, Isbell, Matthew Ray, Baker Hughes Inc. – Innovative PDC
Cutter Technology Leads to Step Out Performance Improvements in Diverse Applications in Shale
Plays.
24. Langeveld, C.J., Shell Research B.V. (1992) – PDC Bit Dynamics
25. Nguyen, D.T., Master Thesis (2012) – Drill bits technology – introduction of the new kymera hybrid bit
26. Boryczko, Piotr – Master Thesis (2012) – Drill bit optimization in exploration well 6507/6-4a in the
Nordland ridge area
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