SPE-11168-MS New Low-Speed High-Torque Motor Experience in Europe

8/10/2019 SPE-11168-MS New Low-Speed High-Torque Motor Experience in Europe

1/16

SP

ociety of

PetN:lleum

Engineersof AIME

n

Europe

John Beswick, Camborne School o Mines, and John Forrest, DR/LEX Aberdeen) Ltd.

Copyright 1982.

Society

of Petroleum Engineers of AIME

This paper was presented at the 57th Annual Fall Technical Conference and Exhibition of the Sow: ty of Petroleum Engineers of AIME.

held n New Orleans. LA. Sept. 26 29. 1982. The material IS subject to correction by the author Permission to IS restricted to an

abstract of not

more than

300 words. Write 6200 N Central Expressway. P.O. Drawer 64706. Dallas.

Texas

ABSTRACT

A

new

generation of multi-lobe positive

d

sp

1acement mud motors des i

gned

in the

USSR has

been used in Europe since

early

1981. A

comprehensive range of experience

has

already

demonstrated the importance and potential of this

development for a wide variety of drilling

applications. This paper describes the design

concept of the motor which operates

on

the Moineau

principle and

discusses

the performance with

reference to a number of recent applications

including

straight

hole

drilling

directional

drilling and coring. The slow-speed high-torque

characteri

sti cs

whi

ch

permit sustai ned hi gh bit

weights give near rotary conditions at the bit

for the

first

time with a

downhole

motor offering

many

advantages in

drilling.

The references

to

case histories include a

summary of the comprehensive use of the motors for

directional

drilling

in two 7000

ft

deep wells in

granite for a hot dry rock geothermal energy

research project in Cornwall UK In addition

comments on

the use of the motors with polycrys

tal

line diamond

and tricone

bits

for straight hole

drilling are presented

together

with a number of

references to coring applications.

The results so

far

demonstrate that longer

runs

faster

dri 11 i ng and

more

successful cori

ng

are possible and that the power-speed

characteristics offer new important operational

options including bottom hole configurations with

drilling assemblies below the motor. The

walk

tendency of the motors in directional drilling

is

opposite to that of turbines and therefore

complements

turbines

for long progressive

corrections

in drilling tangent

sections.

The technical improvements to the

original

design based on

early

operational experience are

outlined

and

future potential applications

discussed.

References and illustrations at end of paper

INTRODUCTION

Since March 1981 a new generation of positive

displacement downhole motors has

been

available

from

a base in Aberdeen Scotland

principally

for

onshore operations in Western Europe and offshore

service in the North Sea. Operations

to

date have

inc 1

uded

oi

l i

e 1d and hard rock dri

11

i ng. I n the

first year 12 motors in tvJO sizes in 00

and

g

in 00

have been

used for

straight

hole

drilling

directional

drilling

coring

milling

and cutting casing. The experience has been used

to refine the design and define manufacturing

parameters for a new range of motors which are

entering

large scale manufacture.

The gran;

te

dri

11 i

ng

undertaken by Camborne

School of Mines Cornwall

was

particularly

significant

both

from

the standpoint of the

success achi eyed ; n dri 11 i ng hard abras

i ve

rock

and

the contribution to the improved design

and

development of the motors.

A

wi de

vari ety of bi

ts

have

been

used whi

ch

have demonstrated that rotary drilling parameters

at

the

bi

t generated by a low-speed

hi

gh-torque

downhole motor unit can give substantial benefits

over alternative tools and methods.

The

paper descri bes the experi ence over the

first 12 to 15 months of operation.

MOTOR DESIGN BASIS

These

multi-lobe

positive displacement motors

were evolved over a development period spanning 10

years.

The objecti

ve

was to generate output

character; st

cs equi va 1ent to those of a

rotary

table. High torque at rotational speeds less than

220 rpm

with power being applied at the bit

enables the motors

to

be used within the scope of

standard drilling practices including existing bit

and mud

systems techno 1ogi es. The techni ca 1 data

given in

this

section

refers to the Orilex in

00

motor.


2/16

2

NEW LOW-SPEED

HIGH-TORQUE MOTOR EXPERIENCE

IN EUROPE

SPE

11168

The output from the hydraul ic

power

unit

is

delivered

via

the

motor bearing system which can

withstand

up

to 55 000 lb weight on bit at

maximum

power. This

is

as

much

as can be used

effectively

by

current roller

cone

bits

or diamond bits

for

bit diameters less than

10

in.

Mud f l ow .rates from 280

to

650 gal m; n are

requi red to generate torque and speed from the

power uni t

fl

ui ds may be either

oil

or water

based.

The

motors can

operate

with foam,

water or

all

drilling

muds with weights

up

to a specific

gravity

of

2.2.

The complete motor unit is contained within an

overall length of 25 ft including

tool crossovers

and a bypass

valve.

This

makes the

tool

ideal

for

directional

drilling. Incorporation of the tool

into

the

drilling assembly is straight forward;

there is

no need

to make up

tool

sect

ions

on

the

drill site.

The

hydraulic power

unit

of

the

multi-lobe

motor compared with

that

of

the

conventional

one-two lobe motor

is

shown

in cross-section in

Figure 1.

The

basic

operating principle is that

of the Moineau

pump.

The detailed application and

development of

this

principle for i ts use as a

dri

11

i ng motor has been researched in the

USSR

since the early 1960 s. This research culminated

in

the Drilex

drilling motor which

is the subject

of this paper.

The motor

operates

i n a manner oppos

i te to

that of

a pump. The screw converts

the fluid

energy of the

mud into

rotational motion to turn

the

drill bit.

The rotational component and

static component must include one elastomer

surface in order to radially seal the chambers

through which the fluid is moving axially. The

rotor and stator have helical spiral forms which

are

exactly

equal in

pitch.

In

cross-section,

the

stator

has one

more

lobe

than

the

rotor. Comparing a one-two and a nine-ten

lobe

rotor

stator assembly shown in Figure 1, the

substantial difference in

fluid

cavity geometry

can be seen.

The

multi-lobe

configuration also generates

the significant

additional

feature of reduction

geari

ng. The

rotor

moves wi

thi

n

the stator

as an

epicyclic gear. The rotor has thus two motions,

precession and rotation.

It

is this feature which

gives the

reduction

in

rotational

speed

and the

increase in output torque which are the principal

attributes of

this

series of

positive

displacement

motors.

The geometry of the motor provides minimum

contact

pressure

between the rotor and stator,

thus considerably

increasing

the l ife of both

components. Furthermore, the rotor runs across

the surface of the stator without any

sl iding,

again eliminating a major source of wear.

Axially

the hel i x angl e

is

arranged

to

ensure

that

the

motor wi 11 start rotati ng and not lock

up

as

is

often the case with other

pos

i t i

ve

di sp 1acement

multi-lobe motors.

The output of the hydraulic

unit

is trans

mitted

to

the

output

shaft

via flexible

couplings

which eliminate the

eccentric

motion of

the

rotor.

The output

shaft

; s centred in the cas i

ng

by the

bearing pack which includes

thrust

and

radial

bearings and a flow control valve which maintains

the

mud

1ubri cati on through the bear; ng pack to

less

than

2

of the total flow through the motor.

The

general arrangement of the motor is shown ; n

Figure 2.

The detailed performance characteristics of

the

Drilex

in

00

tool are given

in

Figure 3.

Thi s

data is

taken from bench

test;

ng a

standard

production tool in the horizontal plane with water

as the test fluid.

The

performance of

the

tool

with

mud is

superi

or to the

values

shown

because

of

the better

rotor-stator

sealing. t

was not

possible to test

the full

performance envelope

of

the motor because the test dynamometer would not

absorb

the

high torque

generated at low rotational

speeds.

A comparison of the operational parameters

between

the

Drilex in 00), Dyna-Orill Delta

1000

in

00

and

the

Neyrfor Turbine

in

00

tools

is

given in Figure 4. This

figure

is based

on

the

best

current data generally available.

Check

measurements of stall torque at

650

gal/min have given

torque

values in excess

of

5200

f t lb.

t

is particularly significant to

note how

1i t t 1e reduct i on there is in rotary speed with

increasing torque up to some 70 of onset of

stall . The

test data

clearly indicates the

following major advantages offered by this

low-speed,

high-torque positive

displacement motor

as a

drill

ing

tool:

Rotary speed

is

proportional to

flow

rate.

Torque

is proporti

ona 1 to pressure drop

for

constant flow rate.

A clear

indication

of normal operation

is

evident

from

standpipe pressure.

The flow

rate

range

is

over

five

to one with a

stall torque of 2500

f t

lb available at

minimum flow.

The low

pressure

drop

across

the motor allows

i t to

be

used without excessive demands on mud

pumps.

The

tool

provi des adequate

torque

for

any

bi t

type within the flow rate range determined by

drilling conditions.

IMPACT OF OPERATIONAL EXPERIENCE

ON

MOTOR

DESIGN

The multi-lobe motor design, developed in

the

USSR

has been used

to

drill over six million

feet

in a wide

variety

of oilf ield applications to

depths

up

to 30 000

ft .

Its introduction in

Western Europe posed several engi neeri ng prob 1ems

mainly

resulting

from the following differences in

approach to drilling:


3/16

SPE 11168

A J

BESWICK and

J

FORREST

3

Drilling muds

Drilling practices

Repair philosophy

Dri

11

i

ng bits

Or;

11

i

ng in the

USSR

contrasts

with Western

practices

particularly in

relation to

the

percentage of

well footage

drilled

with downhole

motors

or turbo

dril l

s.

Over

80

of

all

footage

in

the

USSR is

dril led

in this

way. This

contrasts wi th a

fi gure of

1

ess

than 1

in the

United

States.

In

the

USSR, the

evolution of

downhole power units has had a major

effect on all

aspects of drilling

practices.

Oilfield drilling in the

North Sea uncovered a

variety

of

problem

areas in design

which have

successfully been overcome by the introduction of

minor variations

in

dril l ing practice. The most

si gnifi cant of these resulted

from

the

use

of

diamond

bits incorporating

long

integral blade

stabi l isers.

Using diamond

bits

developed for

turbine

applications

i t was

shown

that

high

penetration

rates could be

achieved

in several

medium

to

hard

formations

by

applying

high weight

on bit in spite of

the

low

rotat

i ona 1 speeds of

the orilex motors. The bit

speed could be

increased by supplementing

the motor speed

by

the

rotary table with additional dril ls tring

rotational speeds

of up to

100 rpm. In some

cases penetration rates of over

six times

those

attained by

rotary dril l ing were achieved with the

multi-lobe motors at the expense

of

a

three

to one

reduct ion

in

motor 1 fe.

The pri

nci pa 1

reduction

in 1He

was

caused by long

integral blade

stabil i sers j ammi ng on the wall of the well

and

the

stator

over-runni ng the rotor. The new

tools

will incorporate

a

feature to

minimise

this

effect.

In

general

attention to detail

and

modific

ation of

assembly

procedure

in the

bearing

and

fl

exi b1e joi

nt

assemb 1

es of

the tool has

increased

the

overall reliability of

the

motors by

over a factor

of

four in 15 months of operations.

Run times exceeding

80

hr in the

most

demandi ng

operations

are now achi eved as a matter

of course

and a maximum motor run time

of

189 hr

has been

recorded.

The principal wear mechanisms

in

downhole mud

motors

are

as

follows:

Erosion damage

Vibration

Axial

loading

Lateral

1oadi

ng

Abrasion damage

Erosion

is

related to fluid volume,

mud

weight

sand content

and

the

type

of solids used

in the muds. It is imperative in tool

design

that

a

11 areas

in

the tool whi

ch have a hi

gh

1oca 1

fluid velocity are either eliminated or coated

to

avoid major

erosion of

components.

Vibration especially

in

hard rock dril l ing

particularly affects

the bearing

casing

and

flexible joints. Incorporation of shock absorbers

in the drilling

assembly can reduce the

effects of

vibration considerably.

Careful

analysis

of

the

dril ls tring

and

bottom

hole

assembly

dynamiCS

could contribute to substantial increases

in

motor

and bit

l i f during dri l l ing operations in

hard

rock.

High axial

loads

are necessary mainly

in

formations

where rock crushing strengths are

high.

Roller

cone

bits require relatively

bit

loading

for

effective

penetration. The 64

in

00

Dri 1ex

too

1 wi 11 permi t a wei

ght

on bi t of over

50 000 lb to be run over long periods.

Lateral

loads are applied

mainly

in

directional control dril l ing. The bearing

design

combines

axial

and

radial supports

which have

successfully contained the effects of

extreme

lateral loading

on

the tools. Important design

considerations are

tool bending

stiffness

and

the

lateral displacement stiffness of the output

shafts

relative

to the casings.

Abras ion

is

a major

aspect of

wear

in

1

cases where solids

control in drilling

fluids

is

poor. Abrasion

accounts

for wear

in all

parts

of

the motors where surfaces

are in

contact. Solids

control in most

applications

in Europe is good and

thus the

effects

of this

element have been

minimised.

The

most

si

gni

fi cant operat

i

on to

i

nfl

uence

tool design

has been the hard rock

dri l l ing

programme for the H R Geothermal Energy Research

Project at Camborne School

of

Mi nes in Cornwall

UK.

Th; s prov; ded an ; dea 1

opportunity

for

engineering

evaluation

of drilling parameters

and

their

impact

on

tool design.

The

overall

wear

rate on

motor components produced a

spares

consumption

rate when translated into cost of

about

three times that

normally

experienced

in

oilfield dri l l ing.

The components

of the tools

affected

and

the prinCipal

causes

of

failures are

summarised in Table

1.

The high

axial

vibrations

set up

by the

insert

bits cutti ng the granite caused both fracture

of

thrust bearings

and

excessive

wear on

tool

jOints.

The

number

of significant

stress

reversals

in

a

motor wi th 100 hr dri 11 i

ng

exceeds 5 x 10

7 ,

whi

ch

means that fatigue

cracking

can

be

a

source of

major

fai lure.

t

is important

to minimise

this

1 ke 1 hood to gi ve an increased tool 1ife and

reduce

the risk

of

catastrophic

tool

failure.

The

flexible coupling on

the

intermediate

shaft between the rotor and output shaft also

suffered

hi

gh

wear

rates. Thi

s

was

mai

nly

caused

by the inert ia loading

from

the

rotor above

these

flexible

joints.

Because

of

the

uniformity of

operating

conditions the

engineering data

from Camborne

is

invaluable

and has

already

been used

extensively

in the

development

of new materials

for the

tool

components and precise definition of design

loadings.


4/16

4

N W

LOW SPEED HIGH TORQUE MOTOR EXPERIENCE IN EUROPE

SPE

11168

The pri nci pa 1 developments now in the course

of implementation are:

Increase of the tool bending

stiffness

Stiffening of the radial bearing assembly

The use of metal and ceramic coatings for

i ncreas i

ng

abrasion resi stance and decreas i

ng

friction

Improved

flexible

coupling design

A

simplified

assembly/dis-assembly procedure

The

elastomer of the

stator and its

bonding

has

proved to

be

parti cul arly successful. Thi s

has

not

been

a

significant

source of failure even

during extreme loading conditions. Elastomers

currently

in use are

suitable

for operating the

motors

at fu

11

power

at fl

ui

d temperatures

up

to

280F.

New

elastomers will shortly

be available

suitabl

e

for

temperatures

up

to 350F. Opera

tional temperature limits can be increased

significantly by effective fluid

cooling.

An advanced desi

gn

study has now been

completed and has demonstrated that the same

performance characteristics can

be

developed in an

even

shorter

tool of the order of

15

ft

long.

APPLICATIONS IN OILFIELD

DRILLING

Operat ions in Europe with Dril ex motors

commenced in March 1981. To date dri 11 i ng has

been

conducted in some

35

locations mainly

offshore in the North Sea.

In

addition

operations

have been successfully

undertaken in

the Middle East, Australia and onshore in the

UK

and

in Europe.

The UK and

North

Sea

locations are

shown in Figure 5.

The average

run

time for the motor

i n a

1

drilling applications

since its introduction

is

57

hr

and is

progressively increasing

as the

optimum

drilling

parameters

and

directional

control

programmes have been established.

This

is

in contrast to the conventional one-two lobe

positive displacement motor applications where run

ti

mes

in the vast majority of cases in the North

Sea

are

still

1ess than 8 hr.

Only

turbo dri

11

s

have established

a

track

record of long

vertical

and tangent sect i on runs. The longest cont i nuous

runs with the low-speed, high-torque positive

di

sp

1acement motors have exceeded

12

hr

and

to

date the longest time between motor overhaul has

been

189 hr.

Few

kick-offs

and

initial directional control

runs

have been

made with the motor in

spite

of the

physical

make

up

and

performance being

ideally

suited

to such applications. This, in common with

other restrictions in application are the

result

of commercial pressures imposed by high offshore

rig and

operational

costs which

to a large extent

prohibit experimentation except where all else

fails.

Only

in the hard rock application

at

the

Geothermal Project in Cornwall, discussed in

some

detail

later

in

this

paper,

was i t

extenSively

used for such operations and with considerable

success.

The hi gh

cost of offshore

operations

forces

operators and

their

contractors

to select

practices and

equipment

which

minimise

trip

time

and maximise

penetration

rates. In addition they

tend to select equipment which has a long track

record in the

industry.

These aspects

also

affect

the selection of

bit

types.

In the

North Sea

po

1

ycrysta

11;

ne and diamond bits

account for a

considerably

greater

market share than

roller

cone

rock

bits

in comparison

to

drilling

operations

worldwide.

Typically, a turbo drill driven bit operating

at 6 rpm and

cutting

3 ft

per hour will

remove

0.01 in per revolution. This

is

a minute

amount

and i t is

possible to

remove

at least five

times

this

amount

per

revolution

i

the drive unit has

the torque to turn the bit.

This experience has been

repeatedly

proven in

medium

formations.

In

one operation

rotary

drilling

was achieving less than 5 ft/hr. With the

same

bit

an ACC shark too th diamond, in 00, 3

TS), a mul ti- lobe motor drilled

12 8 ft

in 61 hr;

an

average of almost

2 ft/hr. The

mud

flow

was

500-550 gal/min, the standpipe pressure was

2600-2800 lb/in

2

, and the weight on

bit was

32

000-40 lb.

Considerable success has also been achieved

using the

new

low-speed

polycrystalline bits where

the

cutting

elements are

mounted

on

pillars

on the

bi t face. Several recent runs of over

8

hr have

now been

achieved. This type of bit gives

considerably

greater flexibility in the selection

of

bit

hydraulics

bit speed

and

weight on bit.

It

can

accommodate

over four times the weight

on

bit

which a high speed

polycrystalline bit

will

withstand for optimum

drilling

conditions.

One

factor

which allows the

penetration

rate

to

be

optimised

is knowing

what

power is

being

developed

at

the

bit.

This

is particularly

true

of

polycrystalline bits

which in general run best

with

light

weight

on

bit.

The

Drilex motor

de

1 vers torque di rect 1y proport i ona 1 to pressure

drop, thus the standpipe pressure indication gives

a

direct

monitor of the bit torque. At low weight

on

bit

the conventional weight

indicator

is

not

sensitive enough

to give a

true

indication of the

cutting

action

at

the

bit. For

example, using a

hi gh

speed

OS 19 bit

in sandstone, a penetration

rate

of

82 ft/hr

was achieved over 8 hr with zero

to

4

lb weight

on

bit indicated. This run was

conducted by controlling the brake from the

standpipe pressure

indicator

a

direct reflection

of

the

torque

at

the

bi

t . Previ

OUS

attempts

to

run the

bit at

the

same

conditions with approx

imate 1y

8

1b

wei

ght

on bit

resu lted in

penetration

rates

from

2 to

3 ft/hr. With this

type of

bit

torque

is

the only parameter

which

i

ndi

cates the cutting act i

on

of the

bi t

Thi s

shows clearly that

the low-speed, high-torque

outputs

from

the multi-lobe motors can achieve the

same order of penetration

rates

as turbo

drilling

provided

that

surface control of the brake

is

based on torque.


5/16

SPE 11168

A

BESWICK

and J FORREST

5

Low-speed polycrystalline

bits require

much

hi

gher torque

than the; r

hi gh

speed

vari ants and

operate with approximately five

times

the weight

on

bi

t

The

development of

thi

s

type

of bit

appears to

be a most significant advance

in bit

technology.

Operations with roller cone

bits to

date have

formed a minor part

of

the initial operational

experi

ence with

the

motors with

the on of

the

geothermal

drilling discussed later.

In

some

600 hr of oilfield dri l l ing, bit

l i fe

overall has

been almost

the

same as that for rotary dril l ing,

but penetration

rates

have been 30

to

250

higher.

Wear rates on bit

bearings

have

in

general

been

higher

than

tooth

wear.

It is

regretable

that

the utilisation of roller

cone

bits

in

the North Sea is as low as i t is as there

are many applications where these bits will give a

cost

effective performance

with

the correct

application, ally the

high speed

journal

beari ng bits.

Another interesting

feature of the

low-speed,

high-torque

motors

is their rotational tendency to

turn to

the right

which

is

opposite

to the

tendency of the

turbo dri

11. Experi ence to date

in the

North Sea format

ions

shows a tendency to

turn right at approximately

0.8/100

ft

This

characteristic can be used

to

supplement the

turbo

dri

11

runs, thus

avoi di

ng the

need for

short

expensive

correction runs.

The

results

to

date i ndi

cate

that

the

low-speed,

high-torque multi-lobe, positive

displacement motor

is

a very

practical general

purpose

drilling tool

for oilfield dri l l ing. In

the

15 month

period

since

their

introduction, well

diameters from

in to

in have been

drilled.

Other operations have included kick-off, milling,

caSing

cutting

and

coring.

The

application

of

the

motors

for coring

has been

outstanding

and

is

discussed

in

more

detail

later.

Drilling

with

the Drilex

motors has

disproven

many

of the

myths

of operati ng

both di

amond or

polycrystalline

synthetic diamond

bits.

Exper

i ence has

shown

that

the

general pri

nci p1 es

of

1

ght

wei

ght

and hi gh speed

on

1y app 1y

to

soft

format ion dri 11 i ng

and

even

in

such cases hi gh

speed

is by no

means

essential.

DRILLING IN GRANITE FOR HDR

RESEARCH

As

part

of

a European

research

programme being

carr; ed out

by

Camborne School

of Mi

nes

(CSM) to

study

permeability

enhancement

in

granite

with

specific

reference

to

hot

dry

rock (HDR)

geothermal energy exploitation, two 7000 f t deep

wells

were drilled entirely

in

granite

at

a s i te

in Cornwall, UK Whil st bottom ho 1e

temperatures

were

only

modest up to

l80

0

n the dril l ing

requirements

were very similar to the programme

recent

1y undertaken

at the Los

Alamos Nat i ona 1

Laboratory

(LANL)

1 ,

2

Access

to

the potential HDR reservoir region

at 7000 ft

required

two wells

to

be directionally

drilled entirely in

granite

to

form a

co-planar

doublet in

a

preferred

direction to suit

the

natural

fracturing

orientation.

The

in slant

ho

1e

sections across the

proposed HDR

reservo;

r

region

were

drilled

at an inclination

of

30

0

to

the vertical with a

vertical

separation of 1150

f t

and

within

a narrow lateral tolerance.

The rock underlying the site is a coarse

grai ned porphyrit;

c two

m; ca

granite contai ni ng

feldspar

(56 ) and quartz

(30 )

with an

average

matrix

grain diameter

normally in

excess of 0.1

in

and containing feldspar

megacrysts

up to 2 in in

1ength. Orthogonal near-vert i

ca

1

joi nt

i

ng

extends

to

depth throughout the

granite

with

occas

i ona 1

mineralisation

in

the vicinity of major

features.

In

general

the

granite

is fresh and character

istically hard,

bri t t le

and abrasive.

The need for a

slow-speed

high-torque down-

hole motor suitable

for

di onal

drilling

with

tungsten carbi

de

insert

rock bi

ts was

recogni sed

in

the planning

stage. For effective

penetration

in

the coarse

granite, hi

gh

bit

loads

were

required

as the optimum cutting mechanism

is

to

crush the

feldspar

crystals

to release the quartz.

Much

of the

directional

drilling at LANL was

achieved by

using

rotary

build-up

assemblies

with

motor dri ven

runs

for

trajectory

correcti on.

As

well as problems associated with

the

mechanical

operat

i on of

the

motors, the speed and wei

ght on

bit limitations

15 000 to 20 000

lb)

of

the

positive

displacement

motors used

Dyna-Drill,

Baker and Navi -Dri 11) resulted

in

high

bit

wear

and hence short runs.

The characteristics of the multi-lobed

positive

displacement

motors and

reports

of

their

use

in

the USSR over several years indicated that

these tools would probably be very

suitable

for

hard rock

dril l ing

as

they

offered

virtually

rotary conditions at the bit.

The

f irst

use of a multi-lobed positive

displacement

motor

in

the CSM

geothermal project

drilling

programme was

for the

l 7 ~

in

ini t ial

entry

drilling

into the fresh granite

in the f irst

well.

Run

in

series

with

the

rotary

table, a motor

driven unstabi1ised

assembly provided

an

effective

means

of dri 11

i

ng the shallow

190 f t

surface

holes

where

the

limited

weight available

resulted

in extremely

high vibration

loads on the

motor.

This early

success

under

the

most

severe

conditions

indicated

that

the

motors would

probably

be suitable for the directional drilling.

For di onal dril l ing, bent sub assemblies

of

1 to were used immediately above

the

motors.

Relatively low

average

build-up

rates

of

1/100

f t

in

the first well lower)

and

1.5/100

f t

in

the second well upper) were

adopted

to

reduce

the- risk

of severe

dog

leg

severi

ty

A

ern

at i

ng

motor bent sub

and rotary

driven

slant or

course maintaining assemblies

were

used to build the required trajectories;

the

number of rotary driven runs was reduced from

that

antici due

to

the superior performance

of the

motor

assemblies.


6/16

6

N W

LOW-SPEED

HIGH-TORQUE

MOTOR

EXPERIENCE IN

EUROPE

SPE

11168

With the exception of the short in surface

hole,

all

the motor runs in the

first

well were

drilled

in the in section.

In

the second well,

frequent but unpredictable geological features

changes in

lithology and

the presence of mineral

i sed joi

nts)

increased the

number

of motor dri

ven

trajectory

correction

runs.

In

addition, four

correction runs were required in the in slant

hole section in the second well due to adverse

geological influences

and

the

tight

tolerance

requi rements. The sharp contrast in dri 11 abi 1 ty

between the unaltered grani te and the weathered

joint

material tended to

deflect

the hole. This

was

particularly so

when the joints ran

sub-parallel to the well

trajectory.

During the drilling of over 14

000 f t

of

granite in

two

wells, 35 motor runs

were

made with

7

in 00

and

in 00 tools. The

main

application

was in a motor driven, bent

sub

assembly for

directional

drilling

but motors

were

also used

for

four coring runs,

three straight

hole runs and

on

one occasion for milling junk.

The

motor dri

ven

runs exc 1

udi

ng

cori

ng

and

milling) are

shown

diagrammatically in Figure 6

and a summary of the overall motor performance

is

given in Table 2.

Motor dri

ven

cori ng runs were made

wi

th

both

diamond

and hybri d ro 11 er cone corebi ts, but the

limited comparative experience and general

unsuitability of

oilfield

equipment for coring

very hard abras i ve format ions

make

compari

son

of

rotating

method

in the granite of

l i t t le

value.

The effective 1

fe

of the motor dri ven

assemblies

was generally controlled by bit

bearing

1

f

e, but

was at

1

east three

times

better

than

achieved with positive displacement motors at

LANL. As

well as the increased

cost

effect;

veness

as

a

result

of

faster

penetration rates

and

reduced

tripping, trajectory

correction runs could

be made over longer lengths providing a high

degree of directional precision. The tools also

proved

an

effective counter against the

unpredictable geological influences.

Bit 1oadi ngs were

generally

in the range of

40 000-60

000

lb 2

to

10

times higher than

would

have been

pract i ca 1 with other tools)

whi ch

gave

penetrat i

on rates

comparable with

rotary

methods

instead of the

normal

reduction expected with

motors. The motors permitted

optimum bit

wei ghts

and

rotary

speeds to

be

used

at all

times and

at

no

time

was

the

penetration rate

sacrificed

for

directional control.

Sustained running

at

excessive

bit

loads greater than the design

1 mit) con tri buted to the

hi gh wear rates

experienced.

The

inherent

reactive

torque characteristic of

this type of tool necessitated the use of a

wireline conveyed steering tool. Although there

are

many

vari

ab

1es

whi ch affect

the

magni

tude of

the

reactive

torque such

as

motor condition, flow

rate,

bit-rock interaction

etc,

the observed

values

were

consistent under

normal

operating

parameters

and

ranged

from 60

to

100

in a

counter-clockwise direction.

During the initial kick-off operations, t was

obvious that the

drilling characteristics

of the

motor driven assemblies required axial

vibration

damping

not only to avoid

damage

to

the

drill

string and surface equipment but also to maintain

consistent tool face heading. Subsequent runs with

shock absorbers placed

just above the

bent

sub

assembly reduced

this

vibration

without pre

judicing

directional

control.

During the

drilling

of the

two

wells in

Cornwall,

26

motor

driven,

bent

sub

assembly runs

were made while

drilling

nearly

5200 ft

of hole

up

to

inclinations

of

30

to the

vertical,

involving

110

round

trips

of the steering

tool.

In-hole

operating time for the equipment totalled 267

hours with only 5 hours downtime due to mal

function of the steering tool including

wireline,

processing equipment

and hoist).

The

fl ush

medi urn used was water contai

ni ng

minimum additives

to

satisfy

environmental

chemistry

constraints and

minimise

drillstring

corrosion,

with high

viscosity

polymer

mud

sweeps

and

occasional use of a

lubricator

to

reduce

drillstring

torque.

In

the initial

drilling

the fluid was

reCirculated, but the general problem of cleaning

the abrasive fine

fraction

containing quartz

contri

buted to the

accelerated wear

of the motor

components. Later dri

11

i

ng wi

th motors was

normally carried out using

open

circulation with

clean water.

A typical sample from the

de-silter

overflow

during a period of extended closed circulation

gave

60 by

wei ght

fi

ner than 60 mi crons 250

mesh)

and

54 fi

ner than

30 mi

crons 400 mesh).

The

cost

of providing

better

solids

control

by

means

of a

more

sophisticated

fluid

cleaning

system or an

inexhaustible

supply of fresh water

is

not inconsiderable, but

any future

planning of

similar wells

must

consider the

relative cost

benefits.

As

well

as damage due

to the abrasive

fi

nes

content in the dri

11

i

ng fl ui

d, the vari

ous

1oadi

ngs

comb;

ned

to

gi

ve severe

operati ng

conditions with high

static and dynamic stresses

and stress

cyel i

ng

conduci ve to materi a 1

fati gue

and abnormal

wear.

There

is

1 t t 1e doubt that the use of these

multi-lobe

positive

displacement motors for the

grani

te

dri

11

i

ng

i n Cornwall contri buted

to

the

re 1

at

i ve 1y

fast

progress

rates

achi

eved and

the

good

directional control. Whilst the damage

to

the

motor components

was costly,

considerable savings

resulted

from

the shorter

programme. Minimal

abnormal drillstring wear occurred

as

a result of

the high proportion of

motor

drilling

in the

deviated

sections

of the wells

and

good

well

geometry permitted the

installation

of

4800

ft and

6000

ft of heavi ly central i sed 9 in production

casing without

difficulty.


7/16

SPE 11168

A BESWICK and FORREST

7

The experience at LANL1,2 provides a good

comparative case

h i s t o r y ~

especially

as the well

g o m t r y ~

hole

size,

bit

types

used and

nature of

the

granitic

rock were similar

to

the conditions

in Cornwall. The records presented for the

latest

two

wells at LANL2 show that positive displacement

motors were used in

the

in holes over the

sect; on

from

6500 ft

to

9880

ft where the angl es

of

inclination

were

generally

in the range

3

to

1

r

to

the vertical.

The well s

at

these depths

were well within the

granite

basement. The bottom

hole rock temperatures

were

between

290F and

370F, somewhat above the 180F experienced in

Cornwall. Notwithstandi ng the differences in

depths and temperatures, the conditi ons exi st i ng

at

the

sites

over the 1ength of wells where the

positive displacement motors

were

used are broadly

similar and therefore

the comparison given in

Table 3 serves

as

a guide to the

relative

performance of

positive

displacement motors.

The overall performance in the hard granite

drilling

in Cornwall was impressive

and

the

multi-lobed motors proved to

be more suitable for

directional

drilling

in the

granite

than any of

the

other

positive displacement motors or

drilling

turbines

currently available. This gives

added

confidence

that directional

wells in hard rock

can

be drilled

accurately

at

reasonable

cost which is

a prerequi site for the future

vi

abi 1 ty of HOR

exploitation. The

performance

is especially

encouraging as the motors used lacked the improve

ments in design and materials which the severe

field

experience in the granite has since helped

to promote. In addition, some of the operating

difficulties and wear

problems can now

be

eliminated or reduced as a

result

of operational

experience.

CORING APPLICATIONS

Cori

ng

operations

have been

conducted

i n

wi de vari ety of conditi ons. Most of the cores

have been cut in the northern North Sea through

the reservoir sections, approximately 500-600

ft

in 1ength, at depths of over

9000 ft . To

date,

the use of downhole motors or turbines for coring

has proved to be unsuccessful or at best

impractical.

However,

coring operations with the

mult i -lobe motors

have been as good as

or

better

than rotary coring without the

attendant

diffi culti

es of severe casi

ng wear

duri

ng

such

operations. Also

the length of core cut in the

single trip has been substantially

increased: the

longest core cut to date bei

ng 112 f t

long

wi

th

100

recovery.

Since

March

1981, over

150

cores have been cut

in

20

operations.

The

overall recovery

rate has

been

over

98 . The

in

00

tool has

sufficient

torque to drive a

120 f t

core barrel in an in

00

well section

at an inclination

of

60

to the

vertical

with

circulation rates less

than

300 gal/min.

This flow rate and a rotational speed of less

than

100

rpm gives ideal coring conditions with

either diamond

or

polycrystalline

corebits.

Only

one core was

washed

out where the operator

insisted

on running over 400 gal/min in an attempt

to increase the coring penetration

rates.

Coring operations are conducted normally with

a flow

rate

of approximately

300

gal/min, a weight

on bit

of 8000-12

000

lb

and

with the

drillstring

rotat

i ng at mi n mum speed approx

i

mate 1y 30-

40

rpm). The correspond; ng motor speed

at

thi s

flow rate

is 80

rpm, gi vng a combi

ned

corebarre 1

rotational

speed of 110-120

rpm.

The exceptionally high recovery

rate

over

98

for the cores cut to date can

be attributed

directly to the continuously applied load

at

the

corebit and the minimisation of high axial

drillstring

vibrations normally associated with

high

drillstring

speeds.

Core

recovery

is

a funct i

on

of a

number

of

parameters, part i cu 1arl y geology. Cor;

ng

rates

achieved

for

various geological formations in the

North

Sea at

production

reservoir levels, some

12

000 ft

deep, are shown in Figure 7.

The

i

nabi 1

ty

to

fi

11 a corebarrel

is

frequently associated with

failure

to

restart

the

operation

after pulling off

bottom to

add further

drillpipe. The downhole motor allows coring

operations to

be

conducted without rotation of the

drillpipe;

controlling

the reactive

torque of the

motor on the drillpipe with tongs.

A cori

ng

assembly can

be

made

up

to

full

corebarrel length to permit

drilling

without

pull ing

off

the bottom.

Thi

s avoids the frequent

j ammi

ng

of the core in

the

inner

barrel,

especially

where shale

;s

present in the

formation. The string may

be

rotated by the

kelly

over the 1ast

30

to 45

ft

to

ensure hang ups

do

not occur

on sections

of the

drillstring as

a

result

of low annular velocities

resulting from

the low flow

rates

necessary for coring.

The multi-lobe motors

have

proven to

be

remarkably

reliable

for coring applications. Over

10

cores are cut

regularly

with

one

motor without

any performance reduction being evident. No

di

fference in corebi t or corebarre 1 1 fe has

been

noted using motor driven assemblies

compared

with

rotary coring procedures.

NOVEL APPLICATIONS

The low-speed, high-torque motor has permitted

the adopt i

on

of some

nove

1 procedures as standard

pract ice. The use of the motors for cori ng with

long

corebarrels has

led to

their

use in

assemblies

where drill collars and

stabilisers

are

run

below

the motor to ensure the

rigidity

of the

bottom hole assembly immediately adjacent to the

bit.

This

has been

used to considerable advantage

in

drilling

tangent

sections

in high angle holes

where i t

is

difficult

to

maintain azimuth and

inclination.


8/16

NEW

LOW-SPEED HIGH-TORQUE MOTOR EXPERIENCE IN EUROPE

SPE

1168

Coring

itself

was a novel application

which

has

now

become

standard practice in cori

ng

deep

deviated wells in the North Sea.

The

quality

and

length of cores has increased significantly by the

adoption of

this

procedure.

The motor has also been used

in France

and

Italy

for

drilling

wells spudded conventionally,

but with a final

trajectory horizontal.

The

high-torque output has permitted the

correct

type

of assembly to

be

run

for this

special

drilling

operat ion. Thi s coupled

wi

th the torque-pressure

drop relationship has led

to

the motors being used

as

a

key

dri

11

i

ng

i

ndi

cator

for moni tori ng and

control of the

operation.

The low-speed

and hi

gh-torque

characteri sti

cs

make

these motors ideal for cutting cas i

ng and

milling fish or junk in the wells. An

added

advantage in these

applications is

the

ability

to

apply high weights to the tool.

CONCLUSIONS

The operat i

ona

1 experi ence

to

date wi

th

low-speed, high-torque downhole motors has

demonstrated a number of significant features

which can

be used to considerable advantage in a

wide variety of

drilling

applications.

The motor

has

universal appl ications in all

aspects of

drilling

from spudding to coring. The

use of multi-lobe motors will undoubtedly increase

considerably and may include a substantial

percentage of future

straight

hole well

drilling.

All

types of

bits

can

be run

including

diamond

and

polycrystalline. Bit

life is

not

signif

icantly

reduced in

spite

of the considerable

increases in rates of

penetration

achieved.

Motor l ife has already

been

increased to over

100

hr and

wi

th progress i

ve

engi neeri

ng

support

and

materi a 1s development

i t is

confi dent 1y

expected

that

a

normal

operat; ana 1 1; fe exceed; ng

150 hr wi 11 be

attai nab

1e

wi

thi n the next two

years.

The basic operating parameters have

been

used

to the

full

in

drilling directional

wells in hard

rock with

roller

cone

bits and have made

a

great

;

mpact on

the

economi

cs of hard rock dri

11

i

ng.

Similar conditions are also common in mining

app

1

cat

ions and are

becomi ng

more

commonplace

in

oil

and

gas exp 1

oitat

ion. Savi

ngs

on

dri

11 pi

pe

wear

are also

significant when

using

downhole

motors,

particularly

in abrasive formations.

The future development of these motors

and

other too 1s s dependent on the adopt i

on

of a

combi ned overall strategy for the development of

MW

systems and controls on axial dynamic response

of

drilling assemblies. The adoption of such

strategi es

put the possi

bi

1

ti

es

wi thi

n reach of

dr;

11

i

ng

the majori

ty

of well s

from spud

to

TO

economically with downhole

positive

displacement

motors.

The multi-lobe

positive

displacement motors

have

p r t i cul ar advantage over the

turbi ne

in

that their

length

is

extremely

short.

Cori ng

wi

th

these

motors has become standard

practice in the North Sea.

t

has a1

so

been

demonstrated in extremely difficult formations in

the Gu lf of Suez.

Over 95

core recovery

is now

being obtained with ease

and

round

trip

times are

mi

ni

mi sed by the use of 90

ft

or

120 ft

core

barrels.

The recent development of low-speed,

high-torque

positive

displacement motors

makes

a

substant a 1

contri

but i

on to drill

i

ng

techno logy.

The

traditional domain

of previous generations of

positive displacement motors for short duration

correction runs has

now been

superseded as the

new

generation of multi-lobe motors can

be

considered

for

all

drilling

applications.

ACKNOWLEDGEMENTS

The authors

wi sh to

thank the

di rectors

of

Drilex (Aberdeen) Limited

and

the sponsors of the

HDR Geothermal Energy Research Programme in

Cornwall, the

UK

Department of Energy

and

the

European

Economic Community

for permission to

publish the information contained in this paper.

Acknowledgement

is

also given to the many

firms

and individuals who have

contributed towards

the success of the various operational

opportunities which have been

so

important in the

development programme. In

particular

Mr T L Brittenham,

who

was responsible for the

directional

drilling, and

Mr P L

Moore

who was

the pr; nci pal dri 11 i ng supervi sor, for the

Camborne

HDR drilling

operation, and also the

She 11

UK

Exp 1orat i

on

and Product ion dri 11 i ng team

based in

b e r d e e n ~

REFERENCES

Br; ttenham T

L

Neudecker J W,

Rowl

ey J C and

Williams R

E:

Directional

drilling

equipment

and

techniques

for

deep, hot

granite

well

s ,

SPE Paper No 9227, presented at the 55th

Annual Technical Conference and Exhibition,

Dallas, Texas, September 21-24, 1980.

2 Williams R

E

Neudecker J

W, Rowley J

C

and

Brittenham T L: Directional

drilling

and

equipment for hot granite wells ,

Sandia/CFEM/OOE International

Conference

on

Geothermal Drilling and Completion Technology,

Albuquerque, New Mexico January

21-23,1981.


9/16

Table 1 - Principal causes of damage

to

motors used for directional drilling in granite

High

High

High

Excessive

Ax;

a

Transverse

Sand

Weight

on

Vibration

Vibration

Content

Bit

By-pass valve internals

p

Rotor

p

Stator assembly

P

Universal joints

2

P

Thrust bearing assembly

S

T P

Bleed valve assembly

S

P

Output radial bearing

assembly

3)

P

S

Centre coupling

p

By-pass spring

p

By-pass valve -

stator

crossover

P

Main shaft - bearing

crossover

P

Lower

shaft

coupling

P

Upper shaft coupling

P

Bearing casing

P

S

Inlet - by-pass crossover

P P

Casing failures

P

P

Primary cause

S

=

Secondary cause

T

=

Tertiary

cause

Table 2 - Sumnary of multi-lobe

positive

displacement

motor

performance in two

7000

ft

wells in granite in Cornwall, U

Hole

diam

Dr; ed

length Rotating hours

Average

rate of

penetration

; n

ft) ft/hr)

1 228 49.1 4.6

4409

278.4

15.8

945

27.8

34.0

* Initial

entry drilling

in 190 f t surface holes where

bit loadings

were

1 mited


10/16

Table 3 - Comparison of

positive

displacement

downhole

motor performance in coarse

grained

granite

Location Runs

LANL Fenton Hill, 30

New Mexico,

USA

CSM Rosemanowes, 27

Cornwa11, U

Total

1ength

ft)

1784

5354

Motors used:

LANL

Fenton Hill

CSM Rosemanowes

Average run

duration

hr)

4.9

11 .3

Average

distance

drill

ed

ft)

59.5

198.3

in Baker 3/4 lobe)

in Dyna-Drill 1/2 lobe)

8 in Navi-Drill 1/2 lobe)

in Drilex 9/10 lobe)

in Drilex 9/10 lobe)

Average

ROP

ft/hr)

12.1

17.6

*

The

performance

summary from

the

CSM

Geothermal Project in Cornwall excludes

the

three

runs with a

l 7 ~

in bit to

drill

the short surface holes as high

bit

loadings

were

impractical

and therefore

the records are

unrepresentative

of

normal drilling conditions.

CONVENTION L ;2 LOBE

MOTOR

DRILEX

9 10 LOBE MOTOR

Fig

1 Comparison of cross section of

9110

lobe and 1 2 lobe motors.


11/16

BYPASS

VALVE

ROTOR

STATOR

POWER

UNIT

INTERMEDIATE

TRANSMISSION

BEARING

PACK

BEARING FLOW

CONTROL VALVE

' ' ' + - - ~ I N

RADIAL

BEARINGS

THRUST

BEARINGS

OUTPUT

SHAFT

BIT

CONNECTION

Fig. 2 General arrangement of Drilex multi lobe motor.


12/16

MUD FLOW

RATE

US gal/min)

500 550 600

4000

3500

Q 3000

+-

+-

W

:J

d

I -

I -

:J

a

I -

3

2500

a

0

0:

2000

0

w

0:

:J

/)

/)

1500

w

0:

0...

1000

500

o

20

40 60

80

100 120 140

160

180

200

ROTATIONAL SPEED rpm

MOTOR

TYPE 6

n

00

DRILEX

FLUID WATER

SPECIFIC GRAVITY 1-0

NOZZLE AREA 034 in

2

AVERAGE

WOB

42,400

4,700

Ib

Tests carried out by Royal Dutch

Shell Engineering Laboratories,

The Hague, Netherlands

Fig 3-Performance characteristics of Drilex 6

3

/4 in 00 motor.


13/16

5000

-

_

4000-

g

.....

~ 3000-

a

2000-

r-

1000 -

o ~ - - ~ - - - - - - - - - - - - - ~ - -

DRILEX DYNA-DRILL NEYRFOR

DEVELOPED

TORQUE

2200-

2000-

1800 -

1600 -

N

1400 -

-

:e

(L

1200 -

0

a

Cl

L IJ

1000-

a:

>

/)

/)

800 -

LU

a

CL

600

-

400 -

200-

o ~ - - ~ - - - - - - ~ - - - - - - ~ - -

ORILEX OYNA-DRILL NEYRFOR

PRESSURE DROP AT MAX TORQUE

800 -

700 -

600

-

E

e

500-

Cl

IH 400-

CL

/)

-

a:

300

-

200

-

100 -

O ~ - - . - - - - - - - ~ - - - - - - ~ - - - -

DRI LEX OYNA-DRILL NEYRFOR

SPEED RANGE(FROM

MIN-MAX

FLOW

800

-

700 -

t:

600

-

~

co

500-

OJ

LU

400

a:

CL

:2: 300-

>

Cl

200

-

100 -

O ~ - - ~ - - - - - - ~ - - - - - - r - - -

ORILEX DYNA-DRILL NEYRFOR

PUMP RATE

DRILEX 6%

inOD

PDM

2 OYNA-ORILL

6Y

in

OD

DELTA

1000

POIV

3 NEYRFOR 7 n 00 TURBINE

Fig. 4-Comparison of performance characteristics of Drilex and Dyna-Drill motors and Neyrfor

turbine.


14/16

Fig 5 Locations where Drilex mUlti lobe motors have been used in the North Sea and onshore U.K.


15/16

:2

I

l

e

UJ

0

--l

u

f=

c:

UJ

>

UJ

>

c:

I-

o

1000

:?QOO

3000

4000

5000

6000

7000

HOLE

SIZE

in)

7 2

1214

10

8 Y

2640

(KOP)

5680 ABP)

5928

5942

7075

HOLE

MD

lKBM

SIZE

ft)

(in)

/ ;

42

171;2

_188

960 KOP)

Rotary runs

Motor runs

KOP

Kick-off point

ABP

Angle built point

WELL 1

Drilled length 7031

ft

Rotary drille d 68

Motor

drilled

32

WELL2

Drilled length 7132

ft

Rotarydrilled 49

12

Motor drilled 51

4390 ABP)

100/

8

_4810

--4856

8

Y

7174

Fig 6-Motor

driven runs

in HDR

geothermal energy drilling programme

in

Cornwall, U.K.


16/16

CONGLOMERATE

QUARTZITE

SANDSTONE

SHALE

QUARTZITIC SANDSTONE

SILTSTONE

SHALE SANDSTONE

SILTSTONE SHALE

CORING PENETRATION RATES ft/hr)

10

20 30

DEPTH: 122 13

,000ft

MUD

PRESSURE:

1800 -24001b/in

2

FLOW

RATE:

320 -350 gal/min

Fig Typical coring penetration rates using multi-lobe motors.

4

Date post:	02-Jun-2018
Category:	Documents
Upload:	drilling-moneytree
View:	218 times
Download:	0 times

SPE-11168-MS New Low-Speed High-Torque Motor Experience in Europe

Documents