vMWD

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vMWD (Measurement While Drilling) is a system developed to

perform drilling related measurements downhole and transmit

information to the surface while drilling a well.

The Measurement While Drilling (MWD) Tool came in to application in

early 1970’s.

Before the introuction of MWD! all sur"ey ata #ere o$taine $y

stopping the rilling process for #ireline logging. %or #ireline logging! #e

ha to stop the rilling process! put the rill pipe on slip! $rea& out 'elly!

lo#er the #ireline tool! retrie"e the tool! rea the sur"ey an plan the

further action. This use to increase the non proucti"e time (T).

The MWD tool transmitte the sur"ey reaing to surface through the mustream in the rill pipe. The rilling process #as stoppe for fe# minutes

an sur"ey reaings #ere o$taine in pump off conition. This sa"e

times to greater e*tent compare to #ireline logging.

The transmission of sur"ey ata though mu stream #as one of the

means. +ther means of transmission #ere electromagnetic an acaustic

#hich #ere e"elope in later stages.

Thus MWD #as consiere a $etter option for sur"ey ata transmission

compare to #ireline proceure.

,nitially the system eli"ere three $asic information- ,nclination! /imuth

an Toolface. These three parameters helpe the irectional riller to

position the #ell correctly to the esire target.

ater! MWD #as euippe #ith 2amma 3ay sensor to etect the natural

raioacti"ity an characteri/e shale presence! gauge to measure annular

pressure #hich are useful in slim hole to etermine 45D! 6train gauge to

measure W+B an torue on $it.

MWD tools can also pro"ie information a$out the conitions at the rill

$it. This may inclue-• 3otational spee of the rillstring

• 6moothness of that rotation

• Type an se"erity of any "i$ration o#nhole

• Do#nhole temperature

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• Torue an Weight on Bit! measure near the rill $it

• Mu flo# "olume

Here I'll emphasize my discussion on MWD based on Positive Mud

Pulse Telemetry.

COMPONN!" O# MWD "$"!M

Telemetry Channel

Transmission System

Power Source

MWD Sensors

Surface Systems

TELEMET! "H#$$EL

Telemetry 5hannels are the channels or meium "ia #hich the o#nhole

ata is transmitte to the surface.

%ollo&in are the transmission channels used (or data

transmission )

ar Wire Metho

4lectromagnetic Metho

caustic Metho

Mu ulse Telemetry

M%D P%&" !&M!'$

Most of the MWD systems commercially a"aila$le are $ase on some form

of mu pulse telemetry.

The ma*or components o( a mud pulse telemetry system are

sho&n in (iure belo&)

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Fig 21.1 Mud Pulse Telemetry Components

The o#nhole components are all house in a nonmagnetic rill collar

(MD5).

The ma*or components are)

(a) a po#er source to operate the tool - it operates the tool #hen #e plan

to ta&e a sur"ey

($) sensors to measure the reuire information8

(c) a transmitter to sen the ata to surface in the form of a coe8

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() a microprocessor or control system to coorinate the "arious functions

of the tool - it po#ers up the sensors! stores the information that has

$een measure an then acti"ates the transmitter to sen the ata in the

form of a coe message.

The sur(ace e+uipment consists o()(a) a stanpipe pressure transucer to etect "ariations in pressure an

con"ert these to electrical signals8

($) an electronic filtering e"ice to reuce or eliminate any interference

from rig pumps or o#nhole motors that may also cause pressure

"ariations8

(c) a surface computer to interpret the results8

() a rigfloor isplay to communicate the results to the riller! or plotting

e"ices to prouce continuous logs

T#$,MI,,I-$ ,!,TEM

ere in transmission system , shall concentrate on the transmission "ia

rilling flui! i.e.! the mu pulse telemetry.

The Mud Pulse Telemetry can be (urther cateorized into )

ositi"e Mu ulse Telemetry (Maximum use in industry )

egati"e Mu ulse Telemetry

5ontinuous Wa"e Telemetry

Positive Mud Pulse Telemetry )

ositi"e mu pulse telemetry (MT) uses a hyraulic poppet "al"e to

momentarily restrict the flo# of mu through an orifice in the tool to

generate an increase in pressure in the form of a positi"e pulse or

pressure #a"e #hich tra"els $ac& to the surface an is etecte at the

stanpipe.

To transmit ata to surface! this "al"e is operate se"eral times! creating

a series of pulses that are etecte $y the transucer! an ecoe $y thesurface computer.

The surface computer initially recogni/es a set of reference pulses! #hich

are

follo#e $y the ata pulses. The message is ecoe $y etecting the

presence or a$sence of a pulse #ithin a particular timeframe. This $inary

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coe can then $e translate into a ecimal result. chart recorer is use

to monitor the seuence of pulses.

Fig 21.2 Positive Mud Pulse Telemetry

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Fig 21.3 Positive Mud Pulse Telemetry

$eative Mud Pulse Telemetry

egati"e MT uses a controlle "al"e to "ent mu momentarily from the

interior of the tool into the annulus. This process generates a ecrease in

pressure in the form of a negati"e pulse or pressure #a"e #hich tra"els

$ac& to the surface an is etecte at the stanpipe.

The rapi opening an closing of this "al"e therefore creates a rop in

stanpipe that can $e etecte $y the pressure transucer.

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Fig 21.4 Negative Mud Pulse Telemetry

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Fig 21.6 Continuous Wave Telemetry

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Fig 21. Continuous Wave Telemetry

P-WE ,-"E,

The MWD Tool &or/s in t&o situations )

(a) When the circulation is +

($) When there is no circulation! i.e. #hile tripping #hen the pump is in

+%% conition.

lso! once lo#ere! the MWD tool is not retrie"e $ac& to surface unless

there is some &in of pro$lem #ith tool.

Thus to continuously pro"ie po#er to the tool! #e reuire a po#er

source.

The po&er source can be )

(a) Batteries

($) Tur$ine lternators

0atteries ) (ithium Battery! usually <= >)

They are compact an relia$le since they contain no mo"ing parts.

They ha"e a finite operational life an are temperatureepenent.

$atteries.

6ince it has no relation #ith rilling flui motion! this ena$les the tool to

operate #hile tripping an also ena$les operation inepenent of mu

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flo# hyraulics.

They ha"e $een successfully use for applications in #hich only

irectional ata are reuire. s they pro"ie a limite po#er output!

they are not preferre #ith multisensor tool.

Turbine #lternators )

With the tren of using multisensor tools for o#nhole sur"ey! tur$ines

are $ecoming more #iely use to pro"ie po#er to the MWD tool.

The flo# of mu through the tool is harnesse $y the tur$ine $laes!

#hich rotate a shaft connecte to an alternator! hence generating

electricity.

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Fig 21.1$ Mud %&reen

The screen may $e positione at the top of the rill string for ease of

access if it reuires to $e emptie or remo"e to allo# passage of #ireline

tools.

MWD ,E$,-,

#n MWD tool is e+uipped &ith the combination o( (ollo&in

sensors dependin upon the re+uirement )

Directional 6ensor

2amma ray 6ensor

Temperature 6ensor

Do#nhole W+B? Torue 6ensorTur$ine 3M 6ensor

Directional ,ensor )

The irectional sensors currently $eing use in MWD tools uses tria*ial

magnetometers an accelerometers.

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Fig 21.1$ #&&elerometers and Magnetometors in 'ire&tional %ensor

These sensors measure the reuire angles of inclination! a/imuth an

toolface.

6ince the magnetometers measure a/imuth relati"e to Magnetic orth!

the correct magnetic eclination must $e applie to the results.

The 5 a*is is aligne #ith the a*is of the tool! an the B a*is efines the

reference for measuring toolface angle.

The angular offset $et#een the B a*is an the scri$e line of the $ent su$

must $e measure $efore running in the hole.

Both magnetometers an accelerometers gi"e "oltage outputs that ha"e

to $e correcte $y applying cali$ration coefficients. The correcte "oltages

can then $e use to calculate the reuire irectional angles.

6ome &in of signal (li&e #hen rill string rotation stops or #hen the

pumps are shut off) are sent from surface to the MWD control system.

The control system after recei"ing such signals po#er up the sensors.

transucer or motion sensor #ithin the o#nhole tool recogni/es this

signal an initiates the sur"ey.

During the time #hen the sensors are actually ta&ing the measurements

the rill string must remain stationary for accurate results to $e

o$taine. This perio is generally less than < min.! after #hich normal

rilling can resume.

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high"oltage electroe (@ 1000 >) runs through the centre of the

cham$er.

s gammarays enter the cham$er they cause ioni/ation of the gas!

creating a flo# of fastmo"ing electrons to#ars the central electroe assho#n in figure $elo#.

Fig 21.13 (eiger)Muller Tu"e

The current of electrons can therefore $e use to measure the amount of

gammarays emitte from the formation.

,cintillation counter )

,t uses a crystal a crystal of thalliumope soium ioie.

The natural gammarays emitte $y the formation passes through the

soium ioie crystal.

The raiation e*cites the crystal! #hich prouces a flash of light orscintillations #hen the gamma ray interacts #ith the crystal.

The light emitte $y the crystal stri&es the photocathoe an releases

electrons.

The electrons tra"el through a series of anoes! causing the emission of

more electrons.

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This generates a "oltage pulse #hich is proportional to the original flash

of light.

The amount of raiation entering the sensor can therefore $e measure

$y counting the num$er of pulses o"er a gi"en time perio.

Fig 21.14 %&intillation Counter

$-TE )

The 2eigerMuller tu$e is not as accurate as the scintillation counter! since

it can only etect a much smaller percentage of the total rays emitte.

,t oes ha"e the a"antage! ho#e"er! of $eing more rugge an relia$le

an $eing cheaper than the scintillation counter.

In addition to providin litholoic discrimination3 the amma ray

sensor provides)

%ormation $e $ounary an thic&ness etermination.

Well to #ell structural correlation of $es.

Depth control an casing seat selection.4stimation of shale fraction in reser"oir roc&s.

primary log for seimentological stuies.

Monitoring of inFecte raioacti"e materials.

Temperature ,ensor

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The temperature sensor is usually mounte on the outsie #all of the rill

collar! an therefore monitors the annulus mu temperature.

The sensing element may $e a strip of metal (e.g. platinum) #hose

electrical resistance changes #ith temperature.

The sensor can $e cali$rate to measure temperatures ranging from A0 to

CA0%.

Do&nhole W-04Tor+ue ,ensor

These measurements are mae $y a system of sensiti"e strain gauges

mounte on a special su$ place close to the $it.

The strain gauges #ill etect a*ial forces for W+B an torsional forces for

torue.

By placing pairs of gauges on opposite sies of the su$! any stresses ue

to $ening can $e eliminate.

Turbine PM ,ensor

When rilling #ith a o#nhole tur$ine! the actual spee at #hich the $it is

turning is not &no#n at surface.

The only effecti"e #ay of monitoring the rpm is to use a tur$ine

tachometer lin&e to an MWD system to pro"ie real time ata.

The o#nhole sensor consists of a <in. iameter pro$e that is place

"ery close to the top of the rotating tur$ine shaft.

+n top of the shaft are mounte t#o magnets 1G0 apart.

s the shaft rotates! an electric coil #ithin the pro$e pic&s up "oltage

pulses ue to the magnets (sho#n in figure $elo#).

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Fig 21.15 Tur"ine *PM %ensor

By counting the num$er of pulses o"er a certain inter"al! the tur$inespee in rpm can $e calculate.

This information is encoe as a series of mu pulses that are transmitte

at inter"als to surface to let the riller &no# ho# the rpm is changing.

,%#"E ,!,TEM,

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6tanpipe ressure Transucer

3ig %loor Display Hnit

3aio Moem

,tandpipe Pressure Transducer )

The stanpipe manifol has a num$er of pressure taps #here gauges

may $e installe.

The transucer can $e installe at a con"enient point $y remo"ing one

of these gauges.

,nsie the transucer is a sensiti"e iaphragm that etects "ariation in

pressure an con"erts these hyraulic pulses to electrical "oltage

pulses.

The "oltage output is relaye to the rest of the surface euipment $y

means of an electric ca$le.

i %loor Display nit )

3ig %loor Display Hnit is a isplay panel installe at the rig floor #here the

irectional sur"ey result (a/imuth! tool face! inclination) are isplaye for

the con"enience of irectional riller.

The rig floor isplay unit is po#ere "ia rig po#er.

,t generally reuires either 1<0> or <=0> po#er supply.

The isplay on 3ig %loor Display unit loo&s as sho#n $elo# -

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Fig 21.1 *ig Floor 'isplay +nit ,nstalled at *ig Floor

adio Modem )

The raio moem is use to communicate #ith the rig floor 3T "ia the

#or&station (aptop).

ll information an ata sent $et#een the t#o components is encrypte

for security purposes.

Fig 21.1- *adio Modem

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Fig 21.22 MW' Components

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Fig 21.23 MW' Tool %euen&e

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Fig 21.24 MW' Tool %euen&e

PO"! ND"

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