New Roller Cone Bit Technology for Geothermal Application

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

2

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

http://en.wikipedia.org/wiki/Geothermal_(geology)

http://en.wikipedia.org/wiki/Ancient_Rome

http://en.wikipedia.org/wiki/Sulphur

http://en.wikipedia.org/w/index.php?title=Fran%C3%A7ois_de_Larderel&action=edit&redlink=1

http://en.wikipedia.org/wiki/Boric_acid

http://en.wikipedia.org/wiki/Leopold_II,_Grand_Duke_of_Tuscany

http://en.wikipedia.org/wiki/Leopold_II,_Grand_Duke_of_Tuscany

http://en.wikipedia.org/wiki/Geothermal_power

http://en.wikipedia.org/wiki/Geothermal_power


3

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°C-

280°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 superheated 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.


4

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.


5

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


6

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


7

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


8

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.


9

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.

http://en.wikipedia.org/wiki/Larderello

http://en.wikipedia.org/wiki/Special:BookSources/1842651250


10

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


11

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

Evaporates, Carbonates

Metamorphic Calcarenite

Metamorphic Limestone

Quartzite, Schist

Granite

350°C

250°C

0 30kpsi


12

Figure 4A – Basic roller cone bit anatomy (left)

Figure 4B – Schematic of seal on journal bearing (right)

Figure 5 – Normal used seal and “cooked” rubber seal (left)

Figure 6 - Histogram of abrasive properties of granite basement formation (right)

Seals

Lubricant

Reservoir

Lubricant

Passageway

Ball Bearings

(Cone Retention)

Ball Hole

API Pin

Leg

Cone

Nozzle

Nozzle Boss

Shirttail

Used rubber seal

“normal wear”

Used rubber seal

“cooked ”

INTERVAL ENEL GreenPower DBOS ANALYSIS

ANALYSIS Travale Sud 1 @Smith Bits - 2006

DRILL

INTERVAL

1800-2000 m

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 meters Total Depth Steps: 401 Depth Steps: Count

Dominant Rock Type: % of Interval

0.0

0.5

1.0121

30.2%

SS

SIL

T

CN

GL

CH

RT

SH

CL

YS

T

CL

AY

MA

RL

CH

AL

K

LS

DO

L

HL

9

2.2%

AN

VO

LC

IGN

E

271

67.6%

ME

TA

PY

RT

CO

AL

Key

5%

95%

Lo. quartile

Up. quartile

Median

Lithology

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 metersTotal values: 401 Skewness: -4.354 Arith. mean: 9.31Within range: 401 Variance: 0.03489 Median: 9.36Geom. mean: 9.308 Kurtosis: 24.58 Mode: 9.500Standard deviation: 0.187 Min. of data: 7.775 Max. of data: 9.48

0.25 2.74

97.0

MT_BIT[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Mill Tooth

DSJ XR+ G VH Not recommended

Mill Tooth

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 metersTotal values: 401 Skewness: 0.9765 Arith. mean: 7.739Within range: 401 Variance: 6.902 Median: 6.591Geom. mean: 7.343 Kurtosis: -0.1224 Mode: 6.500Standard deviation: 2.627 Min. of data: 1.719 Max. of data: 14.39

0.25 0.50 1.002.99

14.7

47.1

3.742.00

3.74

7.23 6.234.99

2.99 2.49

TCI_BIT[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

TCI

00 10 20 30 40 50 60 70 80 90

TCI

Cumulative Formation Abrasion

Low Moderate High V. High

7900.3

Formation Abrasion

Normal Moderate Heavy V. Heavy

Abrasion

Cumulative Formation Impact

Low Moderate High V. High

115.1

Formation Impact

Normal Moderate Heavy V. Heavy

Impact

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 metersTotal values: 401 Skewness: -1.369 Arith. mean: 21911Within range: 401 Variance: 2988403 Median: 22332Geom. mean: 21836 Kurtosis: 3.062 Mode: 22500.000Standard deviation: 1728.700 Min. of data: 12612 Max. of data: 24729

0.25 0.25 0.25 0.50

2.00

3.24

6.73

12.0

19.2

25.925.4

4.24

UCMPS[DBOS];1 (psi) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Unconfined Compressive Strength


0.50 1.75 0.50

35.4

61.8

PDC_DEN[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Blades

4 5 6 7 8 9 10 - 12 13+

PDC Blades


0.25 1.50 0.502.99

32.4

62.3

PDC_CUTT[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

PDC TSD IMPREG

22 mm 19 mm 16 mm 13 mm 11 mm 9 mm Coarse Fine

PDC Cutter

Gage Protection

SD D B SD1 D2 BD

Heel Protection

H OD OD1

Roller Cones Gage Protection

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 metersTotal values: 401 Skewness: 0.5503 Arith. mean: 3.734Within range: 401 Variance: 2.15 Median: 2.744Geom. mean: 3.472 Kurtosis: -1.623 Mode: 2.500Standard deviation: 1.466 Min. of data: 2.259 Max. of data: 5.913

62.3

0.50 2.00

35.2

PDC_PROF[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Fixed Cutter Profile

Long Medium Short Flat

PDC Profile

Well Name: Travale Sud 1 Depth: 1800.00 to 2000.00 by 0.50 meters

LN Porosity


0.25 0.25 0.503.74

95.3

TUR_BLDS[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Blades

4 5 6 7 8 9 10 - 12 13+

Turbo Drill Blades


0.25 0.25 0.50 1.253.99

43.1

50.6

TUR_CUT[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

PDC TSD IMPREG

22 mm 19 mm 16 mm 13 mm 11 mm 9 mm Coarse Fine

Turbo Drill Cutter

PDC Gage Protection

Standard PX PXX

Turbo Drill Gage Protection

Standard PX PXX

26.7

Fixed Cutter Gage Protection


4.95

21.1

56.5

17.4

TUR_BIND[DBOS];1 (none) -

0

100

Cu

mu

lati

ve

Fre

qu

en

cy

%

Bond Material

Soft Medium Hard

Turbo Drill Bond Material

Elastomer wear layer

Elastomer energizer

ear layer

Fluorocarbon wear

layer Dynamic elastomer

wear layer

ear layer

Fluorocarbon wear

layer


13

Figure 7 - Dull or wear indication on offset wells, around 70% of bits have abrasive wear

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)

60

29

28

22

1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0

10

20

30

40

50

60

70

80

90

100

0

50

100

150

200

250

300

350

400

450

500

WT

BT

RG

NO CI

CR

CT

ER

OC

SD

BC

BF

BU

CC

CD

DE

L

FC

HC

JD

LC

LM

LN LT

PB

PN

RO

SP

A

SS

TR

WO

PE

RC

EN

T O

F B

ITS

WIT

H D

UL

L C

OD

E

CO

UN

T O

F O

CC

UR

RE

NC

ES

DULL CONDITION CODE, ALL BITS, BOTH CODES

Performance Study 8 1/2" TCI Bit Enel Tuscany field

COUNT

%

3E

10

11

12

13

14

15

16

17

18

19

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Imp

ac

t Re

sis

tan

ce

-T

ou

gh

ne

ss

Wear Resistance

Carbide Insert Properties - Lab testing data


14

Figure 10 - Average tooth wear location and mode (8 = 100% wear)

Figure 11 - Offset performance for runs in 2008 and 2009, footage drilled, drilling hours and ROP

3.0 3.0

4.0

3.8

1.0

1.0

23

.1%

24

.0%

0%

4%

8%

12%

16%

20%

24%

28%

32%

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

2008, 29 2009, 11

% C

UT

TIN

G S

TR

UC

TU

RE

DE

ST

RO

YE

D/1

00 F

T

AV

ER

AG

E T

OO

TH

GR

AD

E

BIT TYPE, # REPORTED

8 1/2" ENEL performances 2008 to date

INNER OUTER GAGE %CS DESTROYED PER 100 MTR 3E

18

9

17

6

42

.5

39

.0

4.4 5.4

0

10

20

30

40

50

60

70

80

0

50

100

150

200

250

300

350

400

2008, 29 2009, 11

ME

DIA

N H

OU

RS

AN

D R

OP

ME

DIA

N M

ET

ER

S

BIT TYPE

8 1/2" ENEL performances 2008 to date

METERS HRS ROP 3E


15

Figure 12 - Modulus change after 15 hours at 205°C (400°F), fluorocarbon and HNBR rubbers

Figure 13 – Seal FEA output diagram


16

Dual seal technology Single seal technology

Figure 14 – New HT/HP seal package in single and dual configuration

Figure 15 - Load capacity change at 175°C (350°F) shown for high temperature grease and standard grease

-80

-70

-60

-50

-40

-30

-20

-10

0

0 100 200 300 400 500 600

Load

cap

acit

y ch

ange

(%

)

Temperature (F)

High temperature grease Standard grease

Fluorocarbon wear layer

Fluorocarbon energizer

ear

layer

Fluorocarbon wear

layer Dynamic Kevlar®

Fabric wear layer

ear layer

Fluorocarbon wear

layer


17

Figure 16 – Oversize and journal angles on the composite rotated profile view

Offset distance on the horizontal view


18

Figure 17 - Gauge striking distance along hole wall is a function of journal angle, oversize angle and cone-to-bit speed ratio

Figure 18 - Dull grade analysis on Bit Run #3 (hours record) showed good, consistent wear and all major components

#1 cone gauge cutting structure



Cone-to-Bit Speed Ratio


19

Figure 19 - All three bearing, cones and seal hubs Bit Run #3 (hours record) showed no abnormal wear

Figure 20 - All three boots on Bit Run #3 (hours record) were full of grease and in relaxed position

No wear

#1 leg journal bearing #2 leg journal bearing #3 leg journal bearing

No wear

#1 cone #2 cone #3 cone

#1 boot #2 boot #3 boot


20

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

Seal #2 – Moderate ID wear and no OD wear. Had wear on the mud side likely caused by contact with hard granite cuttings

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

#1 seal section

Mud side

O.D.

Bearing side

I.D.

#1 seal portions

Moderate wear

Bearing side

Mud side

Scratches and grooves

on the mud sideScratches and grooves

on the mud side

#2 seal section #2 seal portions

Bearing side

Mud side

Moderate/severe wear

Mud side

O.D.

Bearing side

I.D.

Homogeneous wear

Homogeneous wear

#3 seal section

Mud side

I.D.

Bearing side

O.D.

#3 seal portions

moderate wear

Bearing side

Mud side


on the mud side


on the mud side

minor wear


21

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

58.353.3

34.8

1.8

33.8 32.5

55.8

24.521.5

14.8

6.0

65.8

51.0

27.5

57.5

72.876.5

020

40

60

80

100

120

140

160

180

200

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

HO

UR

S

SEAL/BEARING DULL GRADE

DE

PT

H

Depth Out Depth In Hours

WELL A WELL B


22

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

0

10

20

30

40

50

60

70

80

90

100

0

5

10

15

20

25

30

35

40

45

50

Ave

rage

RP

M

Ave

rage

WO

B (

klb

s)

Mean WOB Well A - Mean WOB Well B - Mean WOB Mean RPM Well A - Mean RPM Well B - Mean RPM

Documents

New Roller Cone Bit Technology for Geothermal Application