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CIT-ChE

Wel l Log Analys is .

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SonicLog

(Acoustic Log )

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Contents

1. Introduction

2. Measurement Principle of Sonic Velocity Log

3. Sonic Response to Typical Formation

4. Sonic Porosity

5. Shale Effects

6. An Introduction to MAC

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(1) sonic velocity log ;

(2) Full Waveform Sonic log ;(3) Vertical Seismic Profile (VSP) log ;

(4) sonic amplitude log ;

(5) down hole noise log ;

(6) sonic image logs .

CNLCIntroduction of sonic logs

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Applications of Sonic Log

Determine porosity and lithology (with or without

other logs);

Determine formation mechanical properties which in

turn can be used to estimate hydraulic fracturingpressures and to evaluate sanding problem;

Measure attenuation of sonic energy to evaluate

fracturing and permeability;

Combine sonic and density logs to produce

synthetic seismic traces;

Combine sonic and check shot surveys to calibrate

surface seismic data with borehole log data.

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Propagation of Elastic Waves

An elastic wave travels

through a medium (solid,

liquid, or gas) as slight

disturbances to theparticles in that medium.

The wave energy will move

the particles parallel to

(compressional) and/or

perpendicular to (shear) the

wave propagation direction.

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P-Wave

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S-Wave

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Stoneley Wave

Stoneley wave is a guided tube

wave with velocity and

amplitude determined by:

Borehole fluid elastic

properties

Formation elastic properties

Formation permeability.

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Presentations and scales

Interval transi t t ime

(t, us/ft)---the timerequired for the wave

to travel

a given distance.

Transit time can be

more elegantly calleds lowness.

Most formations have

tc values of 45 to 150

us/ft, and ts values

of 80 to 200 us/ftSonic logs are

presented on a linear

scale, as shown in

right Figure.

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Measurement Principle of Sonic Velocity Log

The simplest sonic tool

has only one transmitters

and two receivers. This kind

of tool can record the sonic

wave that refracts at acritical angle to borehole

wall and travels along the

side wall .The first arrival

compressional waves arerecorded by two receivers .

The interval transit time

(t) can be used to estimateformation porosity .

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Borehole Compensated Sonic (BCS)

The method above

doesnt work well whensidewall is rough and

the sonde is tilted. A

simple means for

overcoming thisproblem is adding a

transmitter on the other

end , newtc

tc =(tu + tl) / (2*L) will be more reliable .

Where L= span, usually

L=0.5~2 ft .

tc is compensatedt .

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Sonic Response to Typical Formation

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The depth of investigation of a sonic tool is

less than 30 in., so it is subject to borehole

effects. These include:

gas in the borehole fluid, large diameter boreholes,

very slow formations, and

the invaded (altered) zone.

Environmental Effects

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Sonic Porosity

Wyllie Time Averge ( WTA )One of the first relationship proposed to

determine fromtc was by Wyllie : ( TimeAverage )

s =

Wheretma is the pure matrix slowness ;tf is the pore fluid slowness ;Cpis a correction,Cp=1 in hard rocks ,but

in unconsolidated formation better results are

found by using Cp =(tshale /100).

Cp(tf tma )(tc tma )

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Shale Effects

Sonic logs will generally have to be corrected forthe presence of shales before estimatingporosity fromtc. The method is to determine

Vsh from some other source (such as theGamma Ray), and reduce tc by some amountwhich depends on Vsh and tsh. The normalmethod for this is:

(tc)shalecorr= tcVsh*tsh

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Shale and Clay Distribution

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Shale Distribution and Effects ont

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Multipole Array Acoustic Log

The conventionalsonic velocity log onlydeterminates the first

arrival compressionalwave. The followingwave (such as shearwave, Stoneley wave )are now be recorded,its amplitude or waveform has been used forrock mechanicsanalyzing.

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Comp.Shear

Stoneley

Compressional Shear Stoneley

Slowness (us/ft)

us

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Un puits for , ncessite d tre

tub et ciment avant sa miseen production .On a alors

besoin de juger de la qualit

de cimentation , de l

tanchit ainsi ralise ainsi

que de l tat du tubage et du (

ou des ) tubing en placeDans ce but une panoplie de

mthodes se basant sur l

tude de la propagation des

ondes , permet d allerjusqu

l obtention d images de la

paroi du trou de sondage , dela colonne de ciment , de la

face interne du tubage , ou du

tubing ou des deux , de

dtecter les endroits corrods

, percs ou autres DIAGRAPHIES SONIQUES

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ANALYSE

STRATIGRAPHIQUE

ANALYSE

STRATIGRAPHIQUE

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Rock Mechanical Properties

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