1_2_acoustic liquid level measurement 2014

8/10/2019 1_2_Acoustic Liquid Level Measurement 2014

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Acoustic Liquid LevelMeasurement

Fundamentals


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TWM Computes

Distance to Fluid LevelFluidLevel

Gaseous Liquid

Flowing BHP

Gas

Liquid

Pump

Static

Reservoir

Pressure

Casing head pressureMicrophone


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1898

Batcheller

Patent

Locating stuck tubes

in pneumatic mailsystems.

Used Blank Pistol

Timed Round TripTravel Time to a

Stuck Tube


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Gas Gun Patent 1936 (Lehr and Wyatt)

Relation between

acoustic velocity, gas

composition, density

and pressure.


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DeptographC. P. Walker 1937

Objective: determine if there is liquid above the pump


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DeptographC. P. Walker 1937

Photographic Recording of Trace


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Walker Patent,

1937

Methods to Calculate

Depth to Liquid level:

1-Time to tubing catcher

and to liquid echoes.

2-Count collar echoes to

liquid level

3-Measure echo time andacoustic velocity in gas

with resonant tube.


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Sound Waves Basics

Sound waves are caused by a pressure change(increase or decrease) in a gas or liquid.

Sound waves propagate through the fluid at a speedcalled Acoustic Velocity.

Sound propagating in gas is reflected by solids or

liquids in the path of the wave. Sound propagating inside a tube is reflected by

changes in area (increase or decrease) of the tube.

The greater the change in area the larger is the

amplitude of the reflected wave and the smaller theamplitude of the transmitted wave.

The pressure of two waves arriving at the same timeat the microphone will add or subtract depending ontheir polarity.


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Traveling Surface Wave


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Echoes from Diameter (cross section area) Changes

Restrictions

inside tubing

Enlargements

in annulus

Acoustic trace

Acoustic trace

Time

Time

0 ft 4300 ft 5000 ft3000 ft


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Echoes due to Wellbore Area Changes

Hole Enlargement Liquid Flow Through Perfs Open Perfs

Enlargementscauseinversionof pulse echo polarity


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Liquid Leaking from Tubing @ 4056 feet


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Liquid Leaking from Tubing @ 4056 feet

Pump On

Pump Off


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Explosion

PulseGeneration

1. Gas gun chamber is charged to a pressure in excess of

the well pressure. Then the valve is opened quickly to

release gas into well.2. The increase in well pressure generates the pulse.

3. Utilizes an external gas supply to generate the acoustic

pulse.

Pressure Increases

5 psi during a short

time then pressure

wave propagates in

tube.Quick

opening

valve

300 psi 100 psi


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Remote Fired Gas Gun

Detailedschematics and

part numbers at

back of TWM

manual


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12 Volt

250 psi

50 psi

50 psi


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Implosion

PulseGeneration

1. Gas gun chamber pressure is bled to a pressure lower than the wellpressure. Then the valve is opened to quickly admit gas from well.

2. Uses the reduction in wells pressure to generate the sound pulse. Well

pressure should be greater than 100 PSI.

3. External gas supply not necessary.

Pressure

Decreases 5 psi

during a short

time thenpressure wave

propagates in

tube.

Quick

opening

valve 300 psi

100 psi


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Acoustic Pulse

Generators

Modern Acoustic Gas Guns:

1. Compact gas gun

2. Remote-fired gas guns

2aWired, 2b-Wireless

1. 5000 psi gas gun

2. 15000 psi gas gun

Obsolete Acoustic PulseGenerators Include:

dynamite cap

45 caliber blank

10 gauge black powder blank

Comparison of Energy fromGas Gun:

1. 45 caliber = 150 psi

2. 10 gauge = 300 psi

13

42b

2a


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TWM Explosion vs. Implosion Example

Data collected

on a shut-in gaswell JW-131using CompactGas Gun.

Compact GasGun charged to400 Psig togenerate thecompressionacoustic pulse.

Wells casingpressure of 205Psig used togenerateimplosion pulse.

400 Psig Explosion

205 Psig Implosion

RTTT


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Normal WellLiquid Level Echo

Polarity of echo same as polarity of pulse generated by gas gun


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Liquid Level Echo Round Trip Travel Time

RTTT = time for sound to travel from gun to LL and back

Question: what is the Distance to the Liquid Level ??

RTTT

A ti V l it i Ai


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Acoustic Velocity in Air

Speed of sound

1100 FT/Sec

Sound in air travels 1100 feet per second. If a person sees the flash and

hears the BOOM 5 seconds later, then the lightning struck 5500 feet away.

Lightning

See Flash

then, hear

BOOM.


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Acoustic Velocity of GasesDepends on P, T and Specific Gravity: (Charts for hydrocarbon gases)

Velocity = 1400 ft/sec Velocity = 785 ft/sec

400 psi

108 F

Distance to Echoes Calculated from a Known


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Distance to Echoes Calculated from a Known

Average Acoustic Velocity

Restrictions

Acoustic trace

0 ft

0 sect1= 6.000sec

L1= 6 x 1000/2

L1= 3000 ft

t2=8.6 sec

L2= 8.6 x 1000/2

L2= 4300 ftIn Wellbore:

P=100 psi

T=188 F

1.2 gravity

V=1000 ft/sec

A ti V l it d G G it C l l t d f


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Acoustic Velocity and Gas Gravity Calculated from a

Known Distance to Cross-sectional Area Changes

Restrictions

Acoustic trace

0 ft

t2=16 sec

V=8000 x 2/16

V = 1000 ft/sec

P=100 psi

T=188 F

V=1000 ft/sec

5000 ft 8000 ft

Gas gravity = 1.2

0 sec t1=10 sec

V=5000 x 2/10

V = 1000 ft/sec

E l i


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Shot

Liquid

Collar

Collar

Collar

Collar

Collar

Bang!

Explosion

PulseImplosion

Pulse

Change in cross-sectional

area at tubing

couplings cause

sound waves to

partially reflect back

to microphone

Number of collar echoes

per unit time is a

measure of the

acoustic velocity of

the gas in that section

of the well.

Echoes in Well

1 second sec/)/(*sec)/( ftJtftJts


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Count Echoes from

Tubing Collars Ideally should count all

echoes from surface toliquid level and givedepth to liquid asnumber of tubing

joints.

In practice need toextrapolate collarcount since the

amplitude of echoesdecreases to wellnoise level and collarechoes becomeindistinguishable from

noise.

E l i


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Shot

Liquid

Collar

Collar

Collar

Collar

Collar

Bang!

Explosion

PulseImplosion

PulseTWM Adjusts

Echo Polarity

For consistency with

established practice

TWM always showsrestr ic t ions as

down kicks and

enlargements as

up

kicks provided

the shot type:

Explosion or

Implosion is

enteredin data file.


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Processing of Acoustic Reflections in TWM

Reflected Pulsecaused byDECREASE in thecross-sectionalarea IS displayedas an downwardkick on theacoustic trace.

Shot fired

Reflected Pulse

caused byINCREASE in thecross-sectionalarea IS displayedas an upward kickon the acoustic

trace.

Depth scale computed from average acoustic velocity from collar count


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Processing of Acoustic Reflections in TWM

Reflected Pulsecaused by LiquidLevel

RTTT= 14.877 sec

LL @ 293.7 joints

Initial Acoustic Pulse

Reflected Pulsecaused byINCREASE in thecross-sectionalarea at 4017 feetas tubing tapers

down.

End of collar echoescounted by processing

record automatically.

Number of Collar

Echoes from 1.5 to 2.5seconds = 19.53 per

second


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Summary

Sound pressure pulse is generated at surface and pressure

wave travels down the wellbore. Changes in cross sectional area cause sound to be reflected

causing echoes that are recorded vs. time at the surface.

Reflected signal polarity indicates restrictions (down kick) orenlargements (up kick) encountered by the acoustic wave.

Round trip travel time (RTTT) is measured very accuratelyfrom shot to any echo flagged by the dashed vertical marker.

If present, the echoes from the tubing collars are counted asfar as possible down the acoustic record.

A depth scale is defined using the average sound speed forthe gas in the well computed from the collar echoes or fromknown downhole markers.

When tubing collars or known depth reflectors are notpresent the acoustic velocity for the gas is estimated fromgas properties, pressure and temperature.


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Questions ?

1_2_acoustic liquid level measurement 2014

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