DSLT TrainingDSLT Training

ContentsContents

• Introduction to sonic logging

• Physics of measurement

• Hardware Description

• Software Description

• Operational Hints

Why Sonic … ?Why Sonic … ?

• Formation evaluation Porosity estimation

– Primary porosity Lithology identification

– With other tools Gas detection Fractures and permeability Mechanical properties

– Sanding analysis– Wellbore stability

• Cement bond evaluation

• Geophysical applications Synthetic seismograms AVO

Why DSLT?Why DSLT?

• The DSLT tool does: Provide a sonic tool for FTB telemetry Provide the first fully digital sonic tool Provide t and CBL applications with existing

sondes

• The DSLT tool does not: Replace the DSI for shear and Stoneley

applications Replace the SDT tool for array measurement (DSI

is the tool that does so)

DSLT OutputsDSLT Outputs

DSLT with SLS-E or SLS-W 2-ft span BHC T (3-ft to 5-ft) 6-in. span HBHC T 16-bit VDL 3-ft dual gate CBL with fluid compensation 16-bit waveform recording (BHC and HBHC

sequences)

DSLT OutputsDSLT Outputs

DSLT with SLS-F or SLS-Z 2-ft span DDBHC T (8-ft to 10-ft and 10-ft to 12-ft) 16-bit VDL 16-bit waveform recording (DDBHC sequence)

DSLT with SLS-D or SLS-C 2-ft span DDBHC DT (3-ft to 5-ft and 5-ft to 7-ft) 16-bit VDL 3-ft dual gate CBL with fluid compensation 16-bit waveform recording (DDBHC sequence)

DSLC OverviewDSLC Overview

• MAXIS New applications:

– Tool Operation Recorder interface– On-Board-Programming interface

• DSLC New telemetry applications

– DTS telemetry and tool control– Tool Operation Recorder

New sonic tool features– On-Board-Programming– Digital transit-time detection

Wave propagationWave propagation

A pebble dropped into the water will generate waves that propagate radially away from the source.

Wave propagationWave propagationPressure WavePressure Wave

In a similar fashion, the transmitter emits a pressure wave which travels radially in the borehole.

T

R

Wave propagationWave propagationHead WavesHead Waves

An energy source moving through the medium will generate head waves

Wave propagationWave propagationPressure WavePressure Wave

When the pressure wave contacts the borehole, it splits into a compressional component (green), a shear component (red) and a mud wave reflection (blue)

Wave propagationWave propagationHead WavesHead Waves

If the acoustic velocity of the wavefront in the formation is faster than the acoustic velocity of the borehole fluid, the wavefront will become perpendicular to the borehole wall.

The head wave is formed when the wavefront is at right angle to the boundary.

Wave propagationWave propagation

ReferencesAcoustics Online Training

Sonic Online Training

At Rest Compressional Shear

PiezoelectricPiezoelectricReceiversReceivers

When the pressure wave applies force to the piezoelectric material, it generates a potential which is proportional to the pressure applied.

PiezoelectricPiezoelectricTransmittersTransmitters

When voltage is applied to piezoelectric transmitters, they expand creating a pressure wave.

V

SonicSonicWaveformWaveform

Compressional

Shear

Stoneley

When the sonic transmitter is fired, the receiver will see the compressional arrivals first (which are usually in the range of 8-12 kHz), followed by shear arrivals (which are in the order of 1-5 kHz).

The frequency of both arrivals is a function of the formation slowness.

After this, Stoneley arrivals occur (which are guided waves across the borehole).

In slow formations, it is possible not to be able to see the shear arrivals.

t Measurement:t Measurement:Single Tx-Single RxSingle Tx-Single Rx

Knowing only the spacing between Tx and Rx, it is not possible to compute formation slowness as mud slowness is not known, and the distances traveled in the formation (b) and the borehole (a and c) are not known.

T

R

a

c

b

3 f

t

t Measurement:t Measurement:Borehole CompensationBorehole Compensation

TT1 = a + b + c

TT2 = a + d + c

TTformation = TT1 - TT2 = (b - d)

tformation = (b - d) / 2

a

c

c

b

a

d

2 f

t

t Measurement:t Measurement:Sonde Tilt ProblemSonde Tilt Problem

Sonde tilt will introduce errors in the measurement of t as a1 <> a2, and c1 <> c2.

Also (b-d) is no longer equal to the distance between the two receivers of 2 ft, but will be reduced by the cosine of the tilt.

b

d

<2

ft

c1

c2

a1 a2

t Measurement:t Measurement:BHC Sonde ConfigurationBHC Sonde Configuration

By adding a symmetrical transmitter and two receivers set, we compensate for both borehole and tilt effects:

tformation = ((TT1-TT2)+(TT3-TT4))/4

This is the SLS-E sonde

2 f

t 2 ft

t Measurement:t Measurement:DDBHC Sonde ConfigurationDDBHC Sonde Configuration

The results from positions 1 and 2 are added to simulate a BHC measurement:

tformation = ((TT1-TT2)+(TT3-TT4))/4

This is the SLS-D/F sonde

2 ft2 ft

CBL MeasurementCBL Measurement

• CBL is the amplitude at the 3-ft receiver

• Zero bond is like ringing a bell Loud ringing High amplitude

• Good bond is like a blanket on a bell Much quieter Low amplitude sound wave

VDL MeasurementVDL Measurement

• VDL is the wavetrain at the 5-ft receiver

• VDL is an indication of both casing-to-cement bond and cement-formation bond.

Basic Sonic MeasurementBasic Sonic Measurement

2 ft

• An acoustic pulse is sent into the formation

• The time it takes to reach each receiver is measured

• One path is 2ft longer than the other.

• The extra time that sound takes to travel those 2ft is used to determine rock’s acoustic velocity

TTransit ransit TTimeime

• Transit time is: The time it takes sound to travel from the transmitter to the receiver

• Measured in s

• It contains :TTmud1+TTrock+TTmud2

TT3

TT4

DDelta-elta-TT

• The time it takes for sound to travel through a known distance of rock

• measured in s/m or s/ft 2ft

DDelta-elta-TT

• Calculated as the difference between two transit times.

• We know the distance between the receivers 2ft

Waveform vs VDLWaveform vs VDLWF CVDL VDL

Open-Hole waveform shown.

Waveforms & Waveforms & TTransit ransit TTimesimes

Far Receiver (TT3)

Near Receiver (TT4)

Near Receiver TT (TT2 or TT4)

Far Receiver TT (TT1 or TT3)

Transmitted Pulse: To Received Pulses Pulse

The extra travel time is caused by the longer travel path.

TT3 - TT4

Waveforms & Waveforms & DDelta-elta-TT

Far Receiver

Near Receiver

Transmitted Pulse: To Received Pulses Pulse

Extra time required to travel 2ft farther

TT3 - TT4

2ft

TTTTDT 43

Lower

2ftDTTTTT Lower43 OR..

DTLower2ft

BBoreorehhole ole CCompensated Sonicompensated Sonic

• To remove certain borehole effects, we add another transmitter/Receiver set.

• Now since these are identical (but upside down) we can take the average of the two

• This is the BHC Delta-Tor just DT

TT4

TT3TT2

TT1

Sonde-TiltSonde-Tilt

• TT’s, decreased and separated (UT TT’s will be larger)

• First arrival amplitude will be dramatically smaller due to late arrivals on the long side of the borehole.

• Zone of investigation is larger than 2’ DTTilted will be slightly larger than DTTrue.

• E2 Will be slightly wider than normal.

Deviated Well

EccenteringEccentering

• TT’s, decreased.

• First arrival amplitude will be dramatically smaller due to late arrivals on the long side of the borehole.

• Low signal amplitude makes detection difficult since noise amplitude remains the same

Large BoreholesLarge Boreholes

• TT’s, Increased.

• First arrival amplitude will be dramatically smaller due to increased travel time through the mud.

• Low signal amplitude makes detection difficult since noise amplitude could remain the same

• 16 in is the maximum hole size.

22ft

TTTT2ft

TTTT 4321

DDelta-elta-TT : BHC : BHC

ft

μs

2ft2

TTTTTT(TTDT 4321

)()

2ft

TTTTDT 43

Lower

2ft

TTTTDT 21

Upper

2

DTDTDT LowerUpper

BHCBHC && HiRes BHCHiRes BHC

5 in

2 ft

BHC HBHCCBHC

HiRes BHCHiRes BHC

5 in

HBHC

• SLS-EA (WA)’s were not designed to operate in this way.

• The receivers are not exactly 5” apart.A Master-Cal is

required to correct for slight differences. HRSP

HRSPLTUT

Waveforms & Waveforms & DDelta-elta-TT

Far Receivers (TT1 & TT3)

Near Receivers (TT2 & TT4)

Extra time required to travel 2ft farther

DT2ft

2ft2

TTTTTT(TTDT 4321

)()

Waveforms & Waveforms & DDelta-elta-TT- Slow Formations- Slow Formations

Far Receivers (TT1 & TT3)

Near Receivers (TT2 & TT4)

DT Increases in slow formaitons

Faster Rock.

Slower Rock

TTnear

From To to TTnear is also a factor of borehole size

(TTMUD)

The slower the formation, the larger separation

Waveforms & Waveforms & DDelta-elta-TT- Borehole Size- Borehole Size

Far Receivers

Near Receivers

The TT’s decrease due to a decrease in TTmud.DT is not affected.

DTsmall hole.TTnear

From To to TTnear is proportional to borehole

size (TTmud) and formation speed

DT Larger hole.

DetectionDetection

Transit Time

• The transit time is “detected” where the waveform amplitude becomes larger than some threshold. This is called the “First Arrival”

E1 E2

For Open-Hoe Logging, we look for the second peak(E2), since it is usually larger than the first(E1)

Threshold

•Max temp : 300 Deg F.•Not combinable with 60 Hz telemetry frame rate tools.•Digital waveform acquisition only.•DSLC is combinable with SLS-W (E), SLS-Z (F), SLS-C (D) modified sondes (FTB through wired).•CTS telemetry or DTS telemetry (both DTB and FTB interfaces are available in DSLC)..•Fixed digital sampling rate : 10 us.•A/D converter resolution for digital waveform : 16 bits.•Memory size for digital waveform : 510 words (1020 Bytes).•Variable telemetry frame size defined by the user :

- 26 words for the header.- 0 to 510 words ( 1 word = 2 bytes) of data for 2 digital waveforms.- Max of 536 words. (DTFS).

•Telemetry frame rate = 15 Hz.•Firing rate = RATE (15Hz or 7.5Hz …).•2 waveform are acquired per sonic firing.•2 digital waveforms are sent uphole per frame.•TT detection done either downhole by the DSP or uphole by the HOST (DFAD).•2 acquisition modes (WMOD) : DETECTION (digitization interval centered on TT) or FULL (fixed digitization interval).•2 gains : hardware downhole gain and a software surface gain. •Amplitude normalization of the raw waveforms for VDL and waveform presentation.•2 type of waveform recorded : raw and normalized.

DSLT Features SummaryDSLT Features Summary

t Detection Problemst Detection Problems

NM

SG

Threshold

T T

E2

Low amplitude of E2 may cause detection to occur on E4

This is Cycle Skipping

NM

SG

Threshold

T T E2

High noise may cause early detection

This is Noise Detection

CBL Good Bond ResponseCBL Good Bond Response

• In excellent bond conditions, CBL amplitude may be too low that cycle skipping occurs to detect TT on E3.

• In good bond conditions, TT may exhibit what is called TT shrinking

H igh T hreshold

T T

H igh T hreshold

T T

Good Bond

Poor Bond