GRC Paper 92
New Roller Cone Bit Technology for Geothermal Application Significantly
Increases On-Bottom Drilling Hours
Simone ORAZZINI, ENEL Italy, Regillio KASIRIN, Giampaolo FERRARI, Alessandro BERTINI, Isabella
BIZZOCCHI, Robert FORD, Qingxiu LI, Ming ZHANG, Smith Bits, A Schlumberger Company
Keywords: Geothermal, Superheated Steam Roller Cone Bit, Drilling Optimization, Tuscany, Italy
Geothermal Resources Council Annual Meeting October 23-26, 2011 Town & Country Resort & Conference
Center San Diego, California
_________________________________________________________________________________________________________________
Abstract
Geothermal energy has been use for centuries to satisfy general heating requirements. The modern
geothermal plant is powered by production wells drilled to a source rock to produce steam at the surface.
Depending on the location and depth, source formation temperatures vary.
In Tuscany, Italy the operator must penetrate very hard and abrasive sediments to access steam in the
granite basement formation. Historically, this was accomplished with a tungsten carbide insert (TCI)
roller cone bit (RC). Standard geothermal bits and components, including grease and elastomer seals,
are adequate for temperatures up to 150°C (302°F). Beyond these temperatures, the bit’s internal
components and lubricating material can degrade causing bearing failure limiting on-bottom drilling
hours.
In Tuscany, the bottom hole temperature is approximately 180°C (350°F) and in some instances it can
exceed 280°C (536°F). The extreme heat reduces on-bottom drilling hours leading to multiple bit
runs/trips that drive up development costs. The operator required new roller cone technology that would
endure the downhole environment.
To solve this challenge, a series of tests were conducted with temperature resistant elastomers and
grease compounds in a controlled laboratory environment. The experiments resulted in a new line of
roller cone bits equipped with an innovative bearing system that includes new proprietary composite
elastomer seals with Kevlar® fabric and a proprietary high temperature grease formula. These
innovations increased seal life, lubricity and load capacity at elevated temperatures for HT/HP
applications.
The new geothermal bit technology has been run in the Italian application with outstanding results.
Compared to standard roller cone products, the high-temperature bits have greatly increased on-bottom
drilling hours while reducing total bit consumption and costly tripping for bit change out. Since
successful development of the geothermal project is tied to reducing drilling costs, the new bit
technology has significantly improved project economics. The authors will discuss development of the
high temperature seal and grease compounds for drilling the granite basement source rock. They will
also outline changes to the TCI cutting structure, field application, dull grades and bit performance data.
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Background
The Tuscany region of central Italy is geologically active and known for its geothermal productivity.1
The geothermal activity is located in a specific geographic area known as Larderello (Figure 1). The
first evidence of organized use of the geothermal resources in the region dates back to the 3rd century BC
when the Romans used its hot sulfur springs for bathing.
In 1817 a small group of entrepreneurs, led by Francois de Larderel, formed a geothermal firm that used
steam heated cauldrons to extract boric acid (H3BO3) from volcanic mud. At that time Leopold II,
Grand Duke of Tuscany was a supporter of Larderel's technique and made him Count of Montecerboli in
1827. A short time later a town was established for the factory workers and was named Larderello in
honor of Larderel's contribution to the area.2 In 1904 an experiment by local nobleman, Prince Piero
Ginori Conti used steam emerging from surface vents to run a rudimentary generator that produced
enough electricity to power five light bulbs. It was the first ever practical demonstration of geothermal
power. In 1913 the region's first geothermal power plant went into operation and by 1944 five
geothermal plants were installed capable of producing 127 MWe.
Initially, drilling operations could produce adequate steam from a shallow metamorphic carbonate
reservoir (1500m) but in today’s environment producers must drill deeper (3000m-3500m) to reach a
productive and economical reservoir (granite basement). The igneous formation is capable of producing
steam up to 220°C (396°F). Over the last 40 years the operator has invested in geothermal energy
production in the region and has extended exploration into adjoining areas.3 There are now roughly 35
geothermal plants in Larderello with a capacity of 882 MWe (Figure 2). Most recently, the operator has
constructed a sophisticated geothermal plant capable of providing electricity for 55,000 households
while avoiding significant CO2 emission.
Introduction
Modern exploration and exploitation techniques, which began around 1910, resulted in the discovery of
a shallow steam reservoir at less than 1000m in the Larderello area. This sedimentary formation,
composed mainly of limestone and anhydrite, has temperatures of approximately 250°C.4 However,
deep exploration wells must drill through thick sections of highly abrasive metamorphic formations to
reach the granite basement. The service provider’s rock strength software calculates average UCS of
18,000psi from 1000m to 1650m, increasing to 24,000psi from 1650m to 1950m with spikes of
27,000psi and higher until bottoming in the granite reservoir (Figure 3). Production wells reach total
depth at approximately 3500m-4000m where temperatures vary between 300-350°C and pressure
reaches 70 bars. These “superheated steam” reservoirs are contained in metamorphic and intrusive
igneous rocks. In the field, top of granite basement is encountered at approximately 2600m.
Drilling in the superhot granite basement formation is accomplished with tungsten carbide insert (TCI)
roller cone (RC) bits. One way to efficiently fail the hard igneous formations is by crushing it with RC
or by using the grinding action of diamond impregnated fixed cutter bits. To date, the use of
impregnated bits has been limited due to the high cost of impregnated technology. Roller cone bits are
economic, but using them means a reduction in on-bottom drilling hours, resulting in increased bit
consumption. RC on-bottom drilling hours or bit life strongly depends on the bit’s design.
Basic RC consists of numerous components engineered to suit a specific application (Figure 4A). The
most essential component is the sealing system. For the bearing to operate efficiently during the life of
the cutting structure, the sealing system must keep foreign materials (drilling fluid, cuttings etc.) from
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
entering the bearing and prevent lubricant from escaping the bit. Both situations can eventually lead to
bearing failure. Standard seal material is composed of nitrile butadiene rubber (NBR) or highly
saturated nitrile (HSN) materials. However, these synthetic rubbers deteriorate and become hard and
brittle when exposed to temperatures higher than 150°C. This material degradation negatively impacts
the sealing force needed to push the seal face against the seal gland. It is imperative to maintain this seal
to keep lubricant in and foreign materials out of the bearing system.
The bearing/seal schematic shown in Figure 4B depicts a proprietary dynamic rubber seal used in
normal temperature oil and gas applications. On one side the seal’s dynamic elastomer wear layer
contacts the journal. On the other side the seal’s elastomer wear layercontacts against the cone gland.
As sealing force is produced by the energizer material, the dynamic elastomer wear face must endure the
heat and abrasion generated by the rotating surface being sealed. Conversely, the energizer is not a
potential high wear area but it must supply a spring-like pushing energy that keeps the wear surface
firmly in contact with its mating surface on the journal.
Application Challenges
To drill the first exploration wells, a conventional RC sealing system was run but proved unreliable.
Low drilling hours resulted from the total loss of drilling fluids during attempts to penetrate the fractured
granite basement. The loss of drilling fluids caused downhole temperature to fluctuate between 100°C280°C causing the bit to super-heat. However, even when fluid losses were halted, the majority of bits
run were still experiencing seal failure. Laboratory investigation revealed that all rubber components
were being melted and deformed; this condition is referred to as “cooked” (Figure 5). The RC with
cooked seals only drilled 68m in 14.8 hours with an average ROP of 5 m/hr. Afterwards, the seals were
completely destroyed and broken in pieces. The hard and brittle consistency of the seals clearly
indicated rubber degradation, which was probably caused by the super- heated steam reservoir.
To address this problem, an optimization program was set up based on laboratory investigations and
field run data. The objective was to minimize the risk of seal failure and extend the bit’s cutting
structure durability in the hard and abrasive granite basement. Formation characteristics were defined
using a rock-strength software program (Figure 6). Detailed dull-bit grading indicated the majority of
bits run in the application resulted in heavy abrasive wear on the inner and outer rows of the cutting
structure.
To solve this problem, a two-pronged bit development strategy was undertaken to discover lubricant and
rubber compound improvements and to optimize the cutting structure and cutting insert materials. The
studies were conducted using a sophisticated, integrated, and dynamic, engineering analysis software
system to optimize the bit’s cutting structure: a more durable bit with an improved ROP that would
make drilling the granite basement economically viable. The rock strength program indicated the
formation is highly abrasive. Field runs confirmed this analysis, because the majority of offset bits
revealed extensive, abrasive wear (Figure 7).
The cutting structure failures were causing drilling inefficiencies: lowering penetration rates while
limiting total footage was increasing drilling costs. An example of abrasive wear is shown in Figure 8.
A graph of laboratory data on wear resistance, plotted against impact resistance, is shown in Figure 9.
To improve the bit’s total performance, a balance had to be achieved between the carbide’s material
properties.
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Generally, materials can be structured with high-wear resistant materials that have low-impact resistance
or low-wear resistance and high- impact resistance. With RC bit designs, engineers must determine
which material is best suited to improve durability and performance. Additional changes can be made to
improve cutting structure durability, including increasing the number of inserts, changing the offset
angle, or insert geometry. However, material changes are the most common way to increase bit
durability and performance.
Depending on the application, a change to carbide properties can be sufficient to improve cutting
structure durability. However, after review of offset bit runs and performance, the bit design team
concluded that changing the carbide grade would not sufficiently enhance the bit’s performance. The
team concluded: concentrating on the cutting structure failure analysis, which might be causing seal
failure, should be the primary focus of their bit performance improvement initiative.
Offset Performance Study
From 2008 to 2010, a total of 40 runs in the same field revealed that the majority of bits had heavy
gauge wear (Figure 10). The average tooth wear on the inner row cutting structure was T-3 indicating
that 37.5% of the original inserts were worn down (T-8 = 100% wear and T-0 is 0%). The bit’s outer
row or gauge is the row that drills the borehole to full gauge, and it was graded T-4 meaning 50% of
inserts were worn away. A slight increase in gauge durability was observed in 2009, but represented an
insignificant difference when compared to the median of meters drilled, run length, drilling hours, and
ROP recorded in 2008 (Figure 11).
Engineers concluded that a change in carbide grade would not be sufficient to obtain the desired
improvement in bit durability and performance. Efforts were still being characterized by a decrease in
on-bottom drilling hours and run length, which was requiring operators to use multiple bits to drill a
certain section length. As previously discussed, the success of a geothermal well is highly dependent on
keeping drilling costs within budget. To accomplish the performance improvement objective, a strategy
was deployed for field testing.
Bit development strategy:
Test baseline bit with no high-temperature seal package
Optimize granite-drilling cutting structure for durability and penetration rate
Include high-temperature seal package
Include new tungsten carbide material to reduce wear
Geothermal Roller Cone Bit Development
Engineers determined the current standard roller cone technology will perform well at temperatures up
to 150°C. The Italian geothermal application requires a new generation of roller cone bits to efficiently
drill at elevated temperature and pressure. In the application standard RC’s elastomer seals, boots and
grease components lose function and the sealing material, normally composed from hydrogenated nitrile
butadiene rubber (HNBR), becomes stiff and brittle. Standard grease losses lubricity and load capacity
at high temperature because it tends softens and bleeds away from the required areas. The grease
ingredients may also degrade.
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Known solutions to the sealing system for geothermal drilling include open bearing and metal
mechanical face seal. The open bearing product has a short bit life due to early bearing failure caused by
the intrusion of abrasive particles from the drilling fluid. The metal sealed bit encounters problems when
downhole vibration causes cone wobble resulting in seal failure because precise alignment is required
for successful sealing due to the none-resilient nature of the metal material.
New Bit/Sealing System Development
The industry required a new high temperature/high pressure (HP/HT) sealing system for geothermal
roller cone bits. An initiative was launched to develop seals and grease formula that could withstand the
rigors of the HP/HT downhole environment. The work has resulted in new fabric reinforced elastomer
composite seals, reservoirs, grease, bearings and stabilized cutting structures for dynamic balance. Each
individual component is optimized and integrated to ensure the successful functioning of the entire
sealing system. All seal and boot components on the geothermal bits are made of fluorocarbon
elastomer compounds. Specifically, the seals are made from fabric reinforced elastomer composites
formulated from fluorocarbon materials that provide excellent thermal stability and wear resistance.
Laboratory tests show that the mechanical properties of fluorocarbon elastomer compounds are well
maintained at high temperature and the 100% modulus increase is less than 10% after 15 hours at
205°C; whereas HNBR material becomes stiff and brittle with 100% modulus doubled (Figure 12). The
fabric also improves the seal’s wear resistance due to its high abrasion resistance, thermal stability, high
strength and modulus that further increases usable seal service at high temperatures.
Finite element analysis (FEA) was used to design the seal and gland geometry. The FEA input
parameters included seal geometry, cone bore and journal geometries, material properties, seal
deflection, working temperature/loads and differential pressure. FEA geometry optimization was based
on output including contact pressure, seal footprints/void space and seal volume relative to gland
volume. A typical FEA output diagram showing the contact pressure distribution over the seal body is
shown in Figure 13.
The proprietary seal can be used in either a dual or single configuration (Figure 14). This composite seal
contains a dynamic Kevlar® fabric portion, fluorocarbon energizer portion, and fluorocarbon wear
resistant portion. The wear resistant portion is normally static, but if dynamic rotation does occur the
material properties improve wear resistance. In the dual seal system, the primary seal keeps lubricant in
the bearing whereas the secondary seal keeps the bearing area clean from abrasives and drilling fluid.
The pressure regulation between seals is achieved through the special design of the two seals. In
addition, for both dual and single seal packages, the innovative seal gland design is adopted to block the
abrasive particles from entering into sealing area.
Grease is another important component in the sealing system. It is the key to keep bearings/seals
effective until the cutting structure reaches the end of its service life. To ensure lubricity in the
geothermal application an innovative high temperature grease compound was developed from selected
synthetic base oils, lithium and various functional additives to increase load capacity at elevated
temperature. Laboratory test results show that the load capacity of the new high temperature grease
holds consistently up to 260°C (500°F), whereas the standard grease load capacity dropped by 75% at
175°C (350°F) as shown in Figure 15.
The synergistic performance of the high temperature sealing system was confirmed in the laboratory
using custom-designed test apparatus (SWT) in an environment which simulates the downhole drilling
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
conditions such as RPM, temperature, pressure, drilling fluids and misalignment of cone/leg. To be
certified successful, the sealing system must pass all predetermined test criteria. The SWT results have
given a good indication of the seal field performance in most cases.
Cutting Structure Design
To optimize a cutting structure for the geothermal application, engineers started by analyzing the
predominate wear and/or breakage conditions on the dull baseline bit. A bit dynamics study helped
identify the design characteristics that limited field performance. Designers then adjusted the main bit
parameters together with the insert row shape and repositioned the layout to determine the best cutter
configuration to deliver the required performance improvement. In this particular study, abrasive wear
was the main dull characteristic in the gauge and adjacent rows. To improve wear resistance it was
critical to develop a durable cutting structure capable of maintaining equally distributed wear on all the
rows during drilling operations. Additionally, the design must have an equal force distribution among
the rows to prevent unbalanced loads that can lead to premature bearing failure.
The study of the proposed changes was driven, without the need of running iterative field tests, by
several computer simulations. The dynamic modeling system was able to fully reproduce the bit-rock
interaction forces and give useful information about the main physical data necessary to identify actual
bit performance.
In a traditional abrasive RC insert layout, bit companies would increase gauge durability by maximizing
gauge row insert count to improve force sharing and increase carbide volume. But adding TCI and
keeping the clearance between inserts constant involves a larger cone diameter and higher oversize
angle. Increasing the oversize angle has proven detrimental in abrasive rock applications because it can
cause higher gauge row scraping along the hole wall which can have a negative impact on gauge wear
condition. In the new design the goals were reached through an “unconventional” row placement layout
mainly focused on:
Minimizing gauge scraping distance along the hole wall
Maximizing insert density in the area adjacent to gauge (proprietary)
Gauge scraping distance along the hole wall in a traditional abrasive bit design is controlled by
independent layout parameters including journal angle, offset, oversize angle (Figure 16) but also of the
dependent variable cone-to-bit speed ratio. The speed ratio is generally a function of bit parameters and
insert row placement but it’s mainly affected by the journal angle. A low journal angle leads to a
median cone-to-bit speed ratio close to 1.3 while high journal angle brings this median value to
approximately 1.4.
Figure 17 shows a comparison among gauge hole wall striking distance values in function of bit
parameters and cone-to-bit speed ratio variations. It is evident from the analysis to minimize the
scraping effect of gauge row inserts it was necessary to adopt the following design criteria:
High journal angle
Low offset
Low oversize angle
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
At the beginning of the design initiative it was reasonable to question if these described criteria would
have led to an excessive change in cone dynamic cutting action, from a force distribution point of view,
with a consequent decrease in ROP performance. With the help of computer simulation the engineers
introduced additional design changes that increased insert density in the area adjacent to gauge for the
following reasons:
Increase vertical and circumferential force distribution
Increase gauge protection from vertical interaction with rock
ROP preservation compared to the baseline layout
During the analysis, the bits that have this special row allocation showed a shifting of vertical forces
towards the bit axis. This distribution caused the inner rows to aggressively penetrate formation and
drive the cone from a dynamic standpoint, slightly decreasing cone speed ratio. Inner row function is
mainly crushing and the rock breaks under compression. Conversely, cutters adjacent to the gauge row
are in scraping mode resulting in higher circumferential force. The shearing action is more efficient
because the fracturing mode happens under tensile load and this mechanism of fracture requires less
force to fail formation and is preferred in the outer area of the hole bottom. The “unconventional” high
density insert design concept has been successfully tested in a Middle East carbonate application where
ROP improvement was the main focus. The final field results have confirmed laboratory testing and
modeling results:
The new bit parameters minimized the gauge scraping distance along the hole wall resulting in
increased gauge row durability and bit life
Increased insert density in the area adjacent to gauge helped ROP preservation with respect to a
“traditional” layout, and force distribution among the rows, resulted in equally distributed wear
on all the inserts.
The above described layout has also allowed the introduction of diamond material on the gauge row of
one of the test bits(C). The problem of using diamond in a “granite basement” application is the
material’s inability to survive the typical impact loads present during drilling operations.
The design criteria allowed a decreasing of vertical gauge impact force while emphasizing scraping as
the predominant working condition in the gauge rows. In this scenario the diamond insert’s superior
wear resistance relative to tungsten carbide has provided a solid contribution to improving field results.
Field Performance
On Well A, two standard baseline-type RC bits (standard seal) were run. On the first run the baseline bit
showed footage improvement. However after 55 on-bottom drilling hours, variations in drill string
torque forced the operator to pull the bit. Dull-grade analysis revealed two seals effective and one
failure. The cutting structure was graded T4 on inner and T6 on outer rows. A second baseline bit was
run: during which total losses occurred and after 15 hours it was decided to pull the bit due to the loss of
cooling medium at the hole bottom. At the surface, engineers noted that all seals had failed and the bit
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
was dull graded T3 on inner and T5 on outer rows. On the test well a total of nine bits were used to drill
a total section length of 1405m. After reviewing the baseline-bit performance and dull grade, it was
decided to run the new HTHP roller-cone bit in the next well.
The new high temperature roller cone bits were run in Well B with outstanding results. The new sealing
system performed as planned in the geothermal application, as indicated by field data. A total of three
HT roller cone bits, equipped with the single seal configuration, were used in the 8-1/2” hole section and
drilled the hard and abrasive granite at average temperatures between 160°C-175°C with spikes up to
300°C. The three bits displayed superior performance compared to standard roller cone products and
had good overall dull condition (Figure 18), longer bit life and higher total footage drilled. The last bit
run (#3) set a new field record of 76.5 on bottom drilling hours and bit revolutions (300,000 revs).
At the end of the runs the bearing and cone ID showed no abnormal wear (Figure 19) and all three
grease reservoirs were found intact and with all boots in relaxed position (Figure 20). Eight of the nine
bearings were effective with the tested seals showing only moderate wear (Figure 21). The wear
amount was the same on all three seals, indicating good bit balancing. Scratches, grooves and wear
observed on the mud side of all three seals were likely caused by hard and abrasive nature of the granite
formation.
The high temperature grease also provided sufficient lubrication and load capacity for the application, as
no overheating of the bearings was observed. Additional R&D on the high temperature sealing system
is underway and further gains are expected.
Results
The new HT roller cone bits had a positive impact on run length and produced an increase of up to 37%
in on-bottom drilling hours compared to the baseline bits (Figure 22). All three bits had good
performance in terms of overall dull condition, total footage drilled and hours compared to offset bits
run at the similar depth out and in the same field.
The new HT RC seal technology proved superior compared to standard and baseline roller cone
products. On Well A, the nine bits (27 seals total) used to complete the 8-1/2” hole section had a seal
failure rate of 37% or ten of the 27 seals failed. On Well B a total of six bits (standard and HT RC) were
required to complete the 8-1/2”hole section. Total seal failure was calculated at 38% with seven of the
18 seals pulled ineffective, with six failures occurring on two standard RC bits. However, only one of
the nine seals failed on the three HT RC bits run setting a two-well best seal failure average of just 11%.
A comparison of average footage and hours revealed the HT RC bits stayed in the hole longer and
drilled more footage than either standard or baseline bits in both Well A and Well B. On Well A, the
average footage drilled per RC bit (nine bits) was 461ft and 33.9hrs. On Well B the average footage
drilled per RC bit (six bits) was 629ft and 58.5hrs. For the HT RC, total average hours on the three bits
were 765ft and 66.6hrs with a last bit setting a field record of 76.5hrs.
On Well B, WOB (Figure 23) was reduced by up to 40% on the six bit runs to hold back ROP. This
was done at the operator’s request in order to maintain wellbore verticality. In spite of significantly
reduced WOB, penetration rates were just slightly lower than averaged on Well A.
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Conclusion
A new high-temperature seal package for roller-cone bits was developed and run in the geothermal
superheated steam application where temperatures can reach 280°C (530°F) with good results. The
following performance increases were observed:
In test runs against baseline bits, on-bottom drilling hours increased 3% to 37%
Eight of the nine seals were effective on the three bits equipped with the high-temperature
sealing package
Average run length of HT RC bits increased 33% compared to the nine bits run on Well A and
36% better than three standard RC run on Well B
Slight reduction in ROP performance on Well B was due to reduced WOB at operator request to
maintain wellbore verticality
The results obtained from testing high temperature roller cone (HT RC) bits are encouraging and
support continued evaluation in future geothermal wells.
Acknowledgements
The authors would like to express their gratitude to the management of ENEL Italy and Smith Bits, A
Schlumberger Company, for permission to release performance data and the new roller cone
manufacturing process respectively. Also, thanks to Craig Fleming, Smith Bits for his technical writing
and editorial contributions.
References
1. Wikipedia, on-line encyclopedia http://en.wikipedia.org/wiki/Larderello
2. Tiwari, G. N., Ghosal, M. K.: “Renewable Energy Resources: Basic Principles and Applications”
Alpha Science Int'l Ltd., 2005 ISBN 1-84265-125-0
3. Batini, F.: “Experience of ENEL in Geothermal Development in Central America” paper
presented at the Workshop for Decision Makers on Geothermal Projects in Central America,
UNU-GTP, LaGeo in San Salvador, El Salvador 26 November – 2 December 2006.
4. Casini, M., Ciuffi, S., Fiordelisi, A., Mazzotti, A.: “3D Seismic Surveys and Deep Target
Detection in the Larderello-Travale Geothermal Field (Italy)” paper presented at the World
Geothermal Congress, Bali, Indonesia, 25-30 April 2010.
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Figure 1 – General location map, Larderello geothermal area - Tuscany, Italy
Figure 2 – Cooling towers and pipework for geothermal power generation in Valle del Diavolo, Larderello
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
250°C
Evaporates, Carbonates
Metamorphic Calcarenite
Metamorphic Limestone
Quartzite, Schist
Granite
0
30kpsi
350°C
Figure 3 – Lithology column with UCS and temperature gradient
Note: UCS, lithology and temperature correlations are approximate; no log data is available for granite basement
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Elastomer wear layer
API Pin
Lubricant
Reservoir
Elastomer energizer
Fluorocarbon wear
Dynamic
earlayer
layer elastomer
Lubricant
Passageway
Nozzle Boss
wear layer
Leg
Fluorocarbon wear
earlayer
layer
Nozzle
Ball Hole
ENELShirttail
GreenPower
Seals
Ball Bearings
(Cone Retention)
Travale Sud 1Cone
Figure 4A – Basic roller cone bit anatomy (left)
Figure 4B – Schematic of seal on journal bearing (right)
TCI
Well Name: Travale Sud 1
Depth: 1800.00 to 2000.00 by 0.50 meters
Total values: 401
Skewness: 0.9765
Within range: 401
Variance: 6.902
Geom. mean: 7.343
Kurtosis: -0.1224
Standard deviation: 2.627 Min. of data: 1.719
Abrasion
Arith. mean: 7.739
Median: 6.591
Mode: 6.500
Max. of data: 14.39
Used rubber seal
“normal wear”
Used rubber seal
“cooked ”
Low
Moderate
115.1
High
V. High
Low
Cumulative Formation Abrasion
Cum ulative Frequency %
47.1
7900.3
100
14.7
10
3.74
2.00
3.74
7.23 6.23
4.99
2.99 2.49
Normal
Moderate
Heavy
V. Heavy
0
20
30
40
50
TCI_BIT[DBOS];1 (none) -
60
70
80
Formation Abrasion
90
TCI
PDC Cutter Figure 5 – Normal used seal and “cooked”
Roller Cones
Gage
rubber seal
(left)Protection
Figure 6 - Histogram of abrasive properties of granite basement formation (right)
Well Name: Travale Sud 1
Depth: 1800.00 to 2000.00 by 0.50 meters
Total values: 401
Skewness: -3.045
Within range: 401
Variance: 0.4407
Geom. mean: 7.958
Kurtosis: 12.59
Standard deviation: 0.664 Min. of data: 3.826
Well Name: Tr
Depth: 1800.00
Total values: 401
Within range: 401
Geom. mean: 3.4
Standard deviatio
Arith. mean: 7.992
Median: 8.182
Mode: 8.500
Max. of data: 8.729
100
62.3
SD
D
B
SD1
Gage Protection
32.4
Cum ulative Frequency %
0.25 0.50 1.00
00
2.99
12
D2
BD
ORAZZINI, KASIRIN,
FERRARI,
BERTINI,
FORD, LI,
ZHANG
Performance
Study
8 1/2" BIZZOCCHI,
TCI Bit Enel Tuscany
field
500
100
COUNT
450
90
80
350
70
300
60
250
50
200
40
150
30
100
20
PERCENT OF BITS WITH DULL CODE
400
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
1
1
1
22
10
1
29
50
28
60
COUNT OF OCCURRENCES
%
WO
TR
SS
SPA
RO
PN
LT
PB
LN
LM
LC
JD
HC
FC
DEL
CD
CC
BF
BU
BC
SD
OC
ER
CT
CR
CI
NO
BT
RG
0
WT
0
3E
DULL CONDITION CODE, ALL BITS, BOTH CODES
Figure 7 - Dull or wear indication on offset wells, around 70% of bits have abrasive wear
Carbide Insert Properties - Lab testing data
19
18
Impact Resistance - Toughness
17
16
15
14
13
12
11
10
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Wear Resistance
Figure 8 – Dull bit analysis indicates the majority of inserts have abrasive wear after drilling the granite source
Figure 9 - Laboratory test on tungsten carbide insert properties (right)
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
7.0
28%
6.0
24%
5.0
20%
3.0
3.8
16%
3.0
4.0
12%
8%
23.1%
24.0%
1.0
1.0
1.0
2.0
2008, 29
2009, 11
4%
0.0
% CUTTING STRUCTURE DESTROYED/100 FT
32%
4.0
8.0
3.0
AVERAGE TOOTH GRADE
8 1/2" ENEL performances 2008 to date
0%
BIT TYPE, # REPORTED
INNER
OUTER
GAGE
3E
%CS DESTROYED PER 100 MTR
70
300
60
250
50
189
200
40
30
100
20
50
10
4.4
5.4
150
0
MEDIAN HOURS AND ROP
350
176
80
39.0
400
42.5
MEDIAN METERS
Figure 10 - Average
location2008
and mode
8 1/2" tooth
ENEL wear
performances
to date(8 = 100% wear)
0
2008, 29
2009, 11
BIT TYPE
METERS
HRS
ROP
3E
Figure 11 - Offset performance for runs in 2008 and 2009, footage drilled, drilling hours and ROP
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ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Figure 12 - Modulus change after 15 hours at 205°C (400°F), fluorocarbon and HNBR rubbers
Figure 13 – Seal FEA output diagram
15
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Fluorocarbon wear layer
Fluorocarbon energizer
Fluorocarbon wear
layer
Dynamic
Kevlar®
layer
Fabric wear layer
ear
Fluorocarbon wear
earlayer
layer
Dual seal technology
Single seal technology
Figure 14 – New HT/HP seal package in single and dual configuration
Load capacity change (%)
0
-10
-20
-30
-40
-50
-60
-70
-80
0
100
200
300
400
500
600
Temperature (F)
High temperature grease
Standard grease
Figure 15 - Load capacity change at 175°C (350°F) shown for high temperature grease and standard grease
16
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Figure 16 – Oversize and journal angles on the composite rotated profile view
Offset distance on the horizontal view
17
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Figure 17 - Gauge striking distance along hole wall is a function of journal angle, oversize angle and cone-to-bit speed ratio
Cone-to-Bit Speed Ratio
#1 cone gauge cutting structure
#3 cone gauge cutting structure
#2 cone gauge cutting structure
Figure 18 - Dull grade analysis on Bit Run #3 (hours record) showed good, consistent wear and all major components
18
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
No wear
#1 leg journal bearing
#2 leg journal bearing
#3 leg journal bearing
No wear
#1 cone
#2 cone
#3 cone
Figure 19 - All three bearing, cones and seal hubs Bit Run #3 (hours record) showed no abnormal wear
#1 boot
#2 boot
#3 boot
Figure 20 - All three boots on Bit Run #3 (hours record) were full of grease and in relaxed position
19
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Mud side
Mud side
Scratches and grooves
on the mud side
Scratches and grooves
on the mud side
I.D.
O.D.
Moderate wear
Bearing side
Bearing side
#1 seal section
#1 seal portions
Seal #1 – Moderate ID wear and no OD wear. Had scratches and grooves on the mud side likely caused by contact with hard granite cuttings
Mud side
Mud side
Homogeneous wear
Homogeneous wear
I.D.
O.D.
Moderate/severe wear
Bearing side
Bearing side
#2 seal section
#2 seal portions
Seal #2 – Moderate ID wear and no OD wear. Had wear on the mud side likely caused by contact with hard granite cuttings
Mud side
Mud side
I.D.
Scratches and grooves
on the mud side
O.D.
Scratches and grooves
on the mud side
moderate wear
minor wear
Bearing side
Bearing side
#3 seal section
#3 seal portions
Seal #3 - Moderate ID wear and minor OD wear. Has scratches and grooves on the mud side likley caused by the contact with hard granite cuttings
Figure 21 – Seal analysis on Bit Run #3 (hours record) revealed only moderate gland wear
20
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
WELL A
0
WELL B
1.8
20
6.0
14.8
24.5
27.5
32.5
40
33.8
34.8
21.5
55.8
60
51.0
53.3
58.3
57.5
80
76.5
Depth In
Hours
200
Depth Out
180
160
140
120
100
DEPTH
72.8
HOURS
65.8
E-E-E E-E-E E-E-E
--
E-E-E F-F-F E-E-F E-E-E F-F-F F-F-F
--
E-E-E F-F-F F-F-F E-E-F E-E-E E-E-E
SEAL/BEARING DULL GRADE
Figure 22 – 8-1/2” bit record from Well A and Well B showing bit type, run length and ROP Well A and Well B
21
50
100
45
90
40
80
35
70
30
60
25
50
20
40
15
30
10
20
5
10
0
0
Mean WOB
Well A - Mean WOB
Well B - Mean WOB
Mean RPM
Well A - Mean RPM
Figure 23 - Drilling parameter analysis for all 8-1/2” bits: Well A and Well B
Note: Operator requested lower WOB/ROP to maintain wellbore verticality
22
Average RPM
Average WOB (klbs)
ORAZZINI, KASIRIN, FERRARI, BERTINI, BIZZOCCHI, FORD, LI, ZHANG
Well B - Mean RPM