1 3 acoustic liquid level analysis 2014

7/26/2019 1 3 Acoustic Liquid Level Analysis 2014

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Acoustic Liquid LevelMeasurement Analysis


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Time to Distance ConversionThe distance from the gun to a reflector

in the casing annulus isproportional to the Round TripTravel Time (RTTT) for the soundto travel from the gun down to theanomaly and back to themicrophone.

To convert time to distance it isnecessary to determine anaverage acoustic velocity in thegas.

Acoustic velocity may be determinedfrom:a-Collar reflectionsb-Depth of known downholechanges in cross sectionc-Gas gravity or composition


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Marker Flags Most Probable Liquid Level


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1. Most probable Liquid level echo is automatically flagged by the softwarefrom reflected acoustic signals digitally processed, filtered, and displayed

versus time.2. Measured time for the acoustic pulse to travel through the gas from the

surface to the liquid level and reflect back to the surface (round trip traveltime, RTTT).

3. Other echoes that could indicate liquid level are also noted and can be

selected by user.

Acoustic Trace - RTTT


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The indicated acoustic velocity 1156.93 corresponds to that of the gas inthe 250 to 800 ft section of the wellbore. It is obtained from the frequencyof collar echoes (jts/sec) for the record between 0.5 and 1.5 seconds.

Automatic Depth DeterminationDepth to last collar counted ismarked (C) on the acousticrecord.


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Average Joint Length Is Used to Convert jts/sec to ft/sec

AcousticVel=(29.98*2)*18.2482= 1156.93 ft/sec


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Count Echoes from Collars

as Deep as PossibleIn practice need toextrapolate collar countsince amplitude of echoesdecreases and cannot bedistinguished from thebackground noise level.

Apply digital filtering to digcollar echoes out ofbackground noise level


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Automatic Filtering to Count Deep Collar Echoes

1-Program scans through acoustic record in 1second intervals to identify collar echo rate(jts/sec) in each section.

2-Builds a narrow-band filter for first section andfilters the acoustic trace from zero to RTTT toremove noise.

3-Counts identifiable collar echoes.

4-Repeats for all filters built from each section.

5-Displays result for the filter that gives thedeepest collar count.


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Automatic Collar Count Procedure

1 st filterC=131 jts

2nd filterC=124 jts

4th

filterC=124 jts

7 th filter

C=142 jts

Program always displays screenfor deepest collar count.


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Analysis Method: Automatic Collar Count

Average Acoustic Velocity over the time interval where collar echoes werecounted.

Liquid Level Echo

Shot Fired: time = 0First 2seconds

Collar count Stops

Collar count Starts

91% of tubing joints counted


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Accuracy of Results from Automatic CalculationRTTT = 5.329 +/- 0.001 seconds

Number of Joints to liquid = 98.77 +/- 0.1 when collar count is deep

Distance to liquid = 3130.9 +/- (depends on value of average joint length )

When using correct average value ( 29.98 ft/jt) : +/- 3 feet

When default value (31.7) is used : +/- (1.7x98.8) = 168 feet error !!!!!!!!

Accuracy of Automatic LL DepthDepth to last collar counted ismarked (C) on the acousticrecord.


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Automatic Depth- Short Collar CountDepth to last collar counted ismarked (C) on the acousticrecord.


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Analysis Method: Automatic Collar Count

Average joints per Second used to extrapolate to Liquid Level

Liquid Level Echo

Collar count Stops

Collar count Starts

Only 52% of tubing joints counted.Program computesmissing joints.

Extra Noise in Record


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Automatic Collar Count Accounting of Missing Joints

Average Jts/sec or ft/sec over the time interval where collar echoes werecounted.

Liquid Level Echo

Shot Fired: time = 0

First 2seconds

Collar count Stops

Time from zero to firstcollar and from LastCollar to Liquid Level is

converted to number of joints using average jts/sec


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Missing Collars Accounting


Liquid Level Echo


First 2seconds

Collar count Stops

Time to first collar = 0.248 sec.Time to last collar counted= 9.184 sec.Time to LL=14.827 sec.Time from last collar to LL = 14.827-9.184=5.643 sec.

Additional joints=(0.248+5.643)*19.8075=116.69 jtsJoints counted =177

Total joints to liquid =177+116.60 =293.69 jts


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Automatic Collar Count Conversion to Distance


Liquid Level Echo


First 2seconds

Collar count Stops

Joints to liquid level = 293.686 jtsIs converted to Depth to liquid level using the

Average Joint Length entered by user in well file: 31.19 ft/jt

DEPTH TO LIQUID LEVEL = 293.686 jts x 31.19 ft/jt = 9161.24 ft

If default average joint length of 31.7 ft/jt had been used:Depth to liquid level = 293.686 x 31.7 = 9309.84 ftDifference = 9309.84-9161.24=148.6 ft


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Summary of Collar Count Guidelines

C line past 70% of LL time OK

C line short of LL time Not OK - Repeat shot with more pressure

Compute the Average Joint Length for thespecific well and enter in well file instead of using the DEFAULT value of 31.7 ft/jt


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Example Acoustic Records

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Sec

1 0 0

. 0 m

V

PFL _Lot of Gas2

0 1 2 3 4 5 6Sec

1

0 0

. 0 m

V

Average well


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Alternate Methods for LiquidLevel Depth Determination Known or Computed Acoustic Velocity Calculation from known downhole Markers Manual Collar Count


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No Collars or Inside Tubing


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Acoustic Velocity from Gas Specific Gravity


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Estimate Acoustic Velocity from Gas Gravity


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Portable Gas Gravitometer

Dual ranges0.52-1.03 and .097-1.90

specific gravity0.05% of reading


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Portable Gas Composition Analyzer

Accuratelycalculate heating

value, relativedensity, andcompressibility


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Earth Temperature Gradients


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Analysis Method: Acoustic Velocity

Enter Velocity Enter Gas CompositionReference: Acoustic Velocity for Natural Gas, Echometer Company


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Gas SpecificGravity from

Acoustic velocity

Known: Acoustic velocity =1400 ft/sec

Pressure = 400 psiTemperature = 108 F

Gas Gravity = 0.6


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Gas Gravity in BHP Screen

Gravity ofannular gas is

c o m p u t e d

from acoustic

velocity,pressure andtemperature

Gas gravity isused tocompute thegas pressure atdepth of liquidlevel.


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Determine Depth to Liquid Level by Identifying Echoesfrom Downhole Markers (changes in cross-section area)

Tubing Cross-overTubing Anchor

Casing LinerEnd of Casing/Open HolePerforations

Gas Lift MandrelsLanding NipplesPacker Bores

Low and High Pass Filters can be used to enhance echoes


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Depth Determination from Downhole Marker


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LL Depth using the Perforations Upkick Echovs. Automatic Collar Counting

Liquid Level:

PerforationsMarker:LL @ 8004 ft

AutomaticCollar Count:LL@ 7991 ft

Collar count stops early


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Field Data Examples

In Examples group of TWM/TAM software Liner at 5240 feet Coal Bed Methane Well


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Very High Liquid Level

First secondof data is notprocessed fordetection ofliquid level.Software

flags firstrepeat

Operatormustmanuallymove LLmarker to firstecho at o,623seconds


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Manual Counting of Collars

Notice: the 11 pointtick marks displayed inthe lower left window donot line up with collarechoes .


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Manual Selection of Collar EchoesProcedure:

1. Select: Manual Analysis Method.2. Identify 1 second interval to analyze.3. Align leftmost tick mark with one tubing

collar reflection.4. Adjust width11 point dividers to align

most tick marks with the collars.

Before:velocity

758.9 ft/sec

LL 236.42 ftAfter:velocity

1258,3 ft/secLL 391.96


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Extremely High Fluid Level

TWM does not flag correct echo

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Sec

1 0 0

. 0 m

V

Program gives warning that cannotidentify fluid level echo


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Very High Fluid Level

TWM does not flag correct echoManually adjust vertical scale and move marker

First shot at 13:410 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Sec

1 0 . 0

m V

Second shot at 13:470 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Sec

1 0

. 0 m V

V Hi h Fl id L l


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Very High Fluid LevelFluid level echo at 0.259 seconds or about 159 ftManually adjust vertical scale and collar markers


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Multiple Echoes

1 2

3

4

5

Which isLiquidLevel ?

1-upkick

2-down

3-down

4-upkick5-upkick

Assume hole in the Tubing Wave Path Analysis


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Assume hole in the Tubing Wave Path Analysis

RTT1 =6.256 upkick ( -------- )

RTT2=10.714 downkick ( )

RTT3= 2x6.256 = 12.512 downkick

RTT4=6.256 +2x4.458 = 15.172 upkick

RTT5=2x6.256 + 4.458 = 16.97 upkick

1

2

3

4

5

RTTT=6.256

RTTT=4.458

10.714

1 2 3 4 5

Liquid Level ?

Hole in Tubing ?

Dashed arrows indicate polarity inversion


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Field Data Examples

In Examples group of TAM software PFL Coal Bed Methane Well

PFL Anomaly


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Quality Control of Acoustic Survey Data

Inspect the well noise before shooting. If excessive noise exists: Use a larger pressure charge in the gas gun. Close Casing Valve and Determine if Noise from Downhole. Increase the casing pressure to attempt to reduce the noise

level.

Inspect the acoustic trace. If an insufficient liquid level kick is obtained,data is otherwise unsatisfactory, or shot not detected:

Inspect connections and Acoustic Cable Increase the pressure in the volume chamber Increasing casing pressure improves collar and liquid level

response. Shut down Noisy Pumping Unit (Surface Equipment) and Re-

shoot

Dont leave Casing to Flowline valve closed too long. Added pressuremay push Liquid Level below pump in some depleted wells.


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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Sec

3 1

. 6 m

V

300psi

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Sec

3 1

. 6 m

V600psi

Effect of Chamber Pressure


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Low Pass Filter for High Frequency Noise

Highfrequencynoisecaused byinjection ingas lift well

Low pass

filterhighlightsliquid levelandmandrels


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Low Pass Filter for High Frequency Noise

High frequency noise caused by hydraulic pumping unit

Low passfilterhighlightsliquid level

0 2 4 6 8 10 12 14 16 18 20 22Sec

3 . 2

m

V

0 2 4 6 8 10 12 14 16 18 20 22Sec

3 . 2

m V


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Noise Induced byConnection to Tree


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AC Charger NoiseConnection of AC chargerto AC or DC-AC inverter,while acquiring data,may

cause additional noise onacoustic trace.

WithCharger

WithoutCharger


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Pumping Related Noise

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28Sec

1 0 . 0

m V

Pumping speed = 6.38 SPM

Pumping period = 9.404 sec.

9.4 sec 9.4 sec


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T bi Fl id L l @ 98 ft


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Tubing Fluid Level @ 98 ft

Echo from top ofpump and repeat

Acoustic velocity intubing fluid = 4435 ft/sec


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High Pressure Casing Head


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Questions ?

L P H d b G


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Low Pressure Hydrocarbon Gas

Velocity =1130 ft/sec Gravity=0.81

Hi h P H d b G


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High Pressure Hydrocarbon Gas

Velocity=1260 ft/sec

Read fromgraphGravity=0.63

Pressure

= 1000 psig

1 3 acoustic liquid level analysis 2014

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