Schlumb_MWD LWD Basic v imp

Schlumberger Public 4/23/2004

MWD and LWD Introduction

Graham Raeper

LWD Interpretation & Development
Schlumberger DCS Scandinavia

Schlumberger Public

Schlumberger Public 4/23/2004

© Schlumberger 2004 Schlumberger Public
An asterisk is used throughout this presentation to denote a mark
of Schlumberger. Other company, product, and service names may
be trademarks, registered trademarks, or service marks of others.

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Measurement While Drilling Tools Schlumberger Public

– Measure the Direction & Inclination of the wellbore
– Allow drilling tools to be oriented (mud motors,

Whipstocks)
– Provide mechanism for transmitting downhole data

to surface
– May provide Gamma Ray & Drilling Mechanics

measurements
– May provide power for LWD tools

Logging While Drilling Tools

– Measure petrophysical properties

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MWD History Schlumberger Public

• Early Patents Schlumberger Public
•Jakosky patent, 1929
• Otis & Alder, 1955

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First WL log (resistivity) 1927
SP 1931
Induction Resistivity & dipmeter 1947
Density – 1957
SNP (neutron) & compensated density - 1962

First DD in 30’s (1934 for first relief well)

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MWD Evolution Schlumberger Public

– 1960’s – Teledrift tool developed - mechanical inclinometer with
positive mud pulse, still used today

– 1969 – SNEA & Raymond Precision Industries start development
work on mud pulse telemetry MWD system (these projects are
combined to form Teleco in 1972)

– 1978 – Teleco MWD tool commercialized
– 1980 – Schlumberger complete first MWD job in the Gulf of Mexico

-Multi-Sensor MWD tool (D&I/ GR/ RES/ DWOB/ DTOR)
– 1984 – NL Baroid Introduce first 2MHz resistivity tool
– 1986 – First Triple Combo (GR/ RES/ Density Neutron) LWD string
– 1993 – Sonic compressional LWD tools introduced
– 2001 – Seismic while drilling, Formation Pressure while drilling

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Telemetry Principles

Mud

Pressure

Time Positive Pulse: Schlumberger Public
1 BPS
Mud
Continuous wave:
Pressure up to 12 Bits Per Second

Time Negative Pulse: Schlumberger Public
Mud 2 BPS

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Time

Starting with our telemetry, on this slide is represented the PowerPulse
series of MWD tools.

All those tools specifications are listed in the drilling services catalogs that
you were provided. Please refer to this documentation for specifications.

All PowerPulse tools are identical except for the 6” holes where the
standard PowerPulse is replaced by the Vision475 MWD, a combination of
PowerPulse and Vision Resistivity.

The PowerPulse comprises 5 elements, a collar, which only has one plugs
on the outside (the read out port), extenders to allow communication with
LWD tools, a turbine to power the tools, an electronic cartridge to control
turbines and modulator as well as communication with LWD tools, and
finally a unique telemetry system, the modulator.

The way the modulator is working is simple as you can see on the right
side of the slide, it is composed of a stator and a rotor, when the rotor
turns it is closing and opening the gap on the stator thus creating a
pressure wave.

This pressure wave is captured on surface. The interesting thing is that we
are actually not looking at the delta pressure seen on surface but rather at
the frequency of this pressure wave.

This gives us the fastest and the most reliable telemetry on the market
today.

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MWD Inside...

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The MWD Sonde is centered in the collar Schlumberger Public
(Mud flow in the center of the tool for some LWD tools)

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MWD Systems available in different sizes Schlumberger Public

PowerPulse*
Impulse*

SlimPulse*

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Objective: MWD tools available today

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MWD Surveys Sensors

Extender Extender

3 Accelerometers + 3 Magnetometers Schlumberger Public

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MWD Surveys Sensors

Sensor sets arranged orthogonally Schlumberger Public

Inclination Error: Azimuth Error: Schlumberger Public
- Movement - Magnetic parts
- Misalignment of the MWD - LWD Power
- Collar Mass
collar in the wellbore - Collar Hot Spots
- Accelerometer misalignment
- Temperature

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Uncertainties

Well path is computed from surveys by minimum curvature method

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800
400
400 A-2 AH Survey SPIDER VIEW 1600
A-1 H Survey Scale (1 cm = 100 m) 200
A-3 H Plan
NORTH >>> 200 Schlumberger Public
1500

1400

1300

1200

2100
2000
1600 1900
1500
1400
1300
1200
0 2177 1600 Inclination accuracy: 0.1° 0
-200 1700 (FMI GPIT Incl. Acc. = 0.5°)
2000 1800
Default Color 2100
Main 1700
Proposal 1800
Survey 1900

A-2 H Pilot Survey Azimuthal Accuracy: 1° -200
(FMI GPIT Az. Acc. = 2°) -400
2325 -600
2300

-400 2100 2200 1300
2000
<<< SOUTH 19000 2100 1400
1800 2000 1500

1600
1700

-600 A4H Plan

12 GR -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 Schlumberger Public
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<<< WEST EAST >>>

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Link from MWD tool to LWD tools

Extender Extender Schlumberger Public

A BHA must be assembled from tools around 30 ft long

„ A link must be provided for electrical connection to other tools in the string
– SLB use extenders to provide the link to between MWD and other tools
– An alternative method is to use an electrode set into the thread face of the
collar
– Extenders provide both the communication and power link

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Logging While Drilling Schlumberger Public

The goal in developing LWD tools was to provide near
wireline quality measurements while drilling
„ Early MWD tools provided basic electrode (short

normal) type resistivity & Gamma Ray measurements
„ 2 MHz resistivity tools developed to obtain higher

quality resistivity measurement in all mud types
„ Density/ Neutron measurement developed to provide

Triple Combo service – supports large percentage of
wells

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Triple Combo Schlumberger Public

Gamma Ray, Resistivity, Density, Pef, Neutron Schlumberger Public

• Provides
measurements of
most commonly
used wireline
string

• Majority of LWD
logs are not
duplicated by
equivalent wireline
service

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LWD FE Capability - Today…

Measurements Conveyance WL Conveyance LWD Schlumberger Public

Thermal Neutron Ø yes yes Schlumberger Public
Bulk Density yes yes
Azimuthal Density no 16-bins
Photoelectric factor yes yes
Spectroscopy / Sigma yes no
Multi-depth Propagation R 5 outputs 20 outputs
Multi-depth Laterolog R 5 outputs 5 outputs
Azimuthal Resistivity 12-bins 56-bins
Micro-Resistivity Image yes no
Compressional Dt yes yes
Shear Dt yes yes
Seismic Check shot yes yes
VSP Yes yes (memory only)
Formation Pressure yes yes
Fluid samples yes no
NMR yes yes

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Objective: High Service Quality

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LWD Acquisition Workflow - Differences Schlumberger Public
between Wireline and LWD

Wireline
„ Data is directly associated to depth indexes as it is acquired- DLIS
„ Depth is calculated from length of cable in hole - independant

LWD
„ Tools do not know the depth / only surface systems know the bit depth
„ Tools record data in time (clock, resets, shifts)
„ 2 types of acquisition: Real-Time and Recorded Mode
„ Real time data, transmitted by the MWD tool via pressure pulses in the mud
column is associated with depth as it is acquired

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Surface Sensors Schlumberger Public

Depth sensor
SPT
Weight/Torque
Pump press.
Pump stroke
Surf. RPM
Etc…

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The MWD unit

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Signal Demodulation Schlumberger Public
Principles
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Type of signals
„ Downhole (MWD-Motor..)
„ Uphole (Pumps-Rig..)
„ Echoes & Reflections
„ Electrical Noise

Characteristics
„ Frequencies
„ Attenuation
„ Direction

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DSPScope

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DSPScope Spectrogram

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Demodulation

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Objective: Understand Demodulation
The Frame Display function is the parent application of SPM Demodulation. This
application performs the following functions:
• Translates the raw bits demodulated by the receiver module into raw data point
values (D-points).
• Sends the D-points to the IDEAL backend.
• Displays the decoded frame and decoding status.
The Frame Display application also contains a toolbar to launch or open the
associated window of many of the SPM Demodulation functions. Simply clicking
on one of the toolbar buttons displays the appropriate control window.

The Frame Display window displays any number of previous frames and is only
limited by screen size. Simply resizing the window with the mouse covers or
uncovers as much frame history as desired. The values are displayed in raw
decimal format. The conversion to engineering units occurs after being sent to
IDEAL.
The Frame Display window displays the most important demodulation
information on the screen. You can check the
• Decoded raw D-points
• Sync status (In Sync, Out Of Sync Pump Down, Signal Loss, Searching, or
Precursor)
• History decoded frame quality
• Frame ID

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Telemetry is Key

Drilling Optimisation Data…

70 50

65 Increased rate of penetration
40

60

55 30 Stick Slip
20
CD&I50

45
40
PWD INCL (deg)
AZI (deg)
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(/m)
35
10

30

25 0
1500 2000 2500 3000 3500 4000 4500 5000

MD(ft)

Formation Evaluation Data…
1 bit per second 3 bits per second 6 bits per second

QC Data High Res

Or 2.2 BPS log and a Or 4.3 BPS log and a
Real-time density image Real-time resistivity

image

Advanced LWD (m/hr) Schlumberger Public

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0.8 BPS 1.7 BPS

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Recording Mode Acquisition Rate Schlumberger Public

To record 2 samples/ft Schlumberger Public
with an acquisition
rate programmed at 10
sec, your ROP have to
be limited to180ft/hr
(60m/hr)

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Read-Out Port (ROP)

ROP Communication with tool Schlumberger Public
to downlaod memory
Battery switch (LWD) Schlumberger Public

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Data vs Time -> Data vs Depth Schlumberger Public

Depth vs Time + Data vs Time = Data vs Depth

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Time to Depth Conversion Depth Based Data

Time Based Data

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HOUR

0.00 Gamma Ray 150.00 Schlumberger Public

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Errors from Time/Depth merge Schlumberger Public

To present recorded LWD logs, the data (recorded downhole against time) needs to be
combined with a surface measurement of depth (also recorded against time).

This can lead to additional errors due to the incorrect alignment of the two independently
recorded times:

„ The clocks might be incorrectly synchronized.
„ Clocks are not perfect, and will drift.
„ Clocks can “reset”, causing jumps.

Each of these effects cause unpredictable effects on the log.

However, the time/depth merge can easily be checked by comparing the RM
data with the RT data.

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Depth Tracking

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Depth Acquisition Schlumberger Public

Any changes in depth entered Schlumberger Public
by the engineer is reported

Depth encoders

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4/23/2004 Depth Log / Tracking Sheet

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Depth - What does the Client Want? Schlumberger Public

True Depth Schlumberger Public
Absolute Depth
Relative Depth
Reproducible Depth

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Which Depth is That?

What is the depth of this formation top?

Wireline depth, Schlumberger Public
attempt 2
Driller’s depth

True depth

Anadrill’s depth
at time t2

33 GR Anadrill’s depth Schlumberger Public
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Wireline depth,
attempt 1

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LWD Depth vs Wireline Depth Schlumberger Public

Wireline depth is the Geoscientist’s reference. Driller’s depth is
the Driller’s reference.

If Wireline depth is corrected properly, it is more accurate; but
those corrections are difficult to apply, and are often
incomplete. The corrections are greater than the inaccuracy
of driller’s depth.

The industry does not want two different measurements of the
same thing. They want a repeatable measurement.

Depth is our most important measurement.

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Depth Measurement Schlumberger Public

LWD’s depth is the driller's depth.

There are 3 different areas that affect the accuracy of LWD depth (closeness to
true value):

1. Difference between driller’s depth and true depth.
2. Difference between LWD’s measurement of depth and

driller’s depth
3. Errors caused by the incorrect alignment in time of the depth

file and the data file (time/depth merge problems)

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Difference Between Driller’s Depth and Schlumberger Public
True Depth

Driller’s depth comes from measuring the length of pipe in the
derrick. Effects it does not account for include:

„ Drillpipe stretch
„ Thermal Expansion
„ Ballooning effects
„ Errors in the measurement

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ddeetteerrmmininininggbbeeddtthhicickknneesssseessaanndd
ggeeoosstteeeerrininggaapppplilcicaattioionnss

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•Additional errors are introduced when
measuring the depth of deviated holes
as the pipe does not lie in the center of
the hole.
•Errors are also introduced in the
conversion from measured to true
vertical depth.

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Summary of stretch calculations

Horizontal Well. Schlumberger Public

A well was analyzed using drilling engineering software. The well was vertical to 3000
ft. Then, it built at 3 deg/100 ft to 38 degrees, which was held until 13000 ft. It built again
at 3 deg/100 ft to 90 degrees This was achieved at 14679 ft. Total depth was 17960 ft.

The following results were obtained from the analysis for the amount of pipe stretch:

Sliding into the hole 3.75 ft

Reaming into the hole at 200 ft/hr 8.67 ft

Rotating off bottom 8.75 ft

Reaming out of the hole 9.08 ft

Sliding out of the hole 13.52 ft

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Difference between LWD’s measurement of Schlumberger Public
depth and driller’s depth

Draworks sensor, Geolograph and/or Rig Motion Sensor
(RMS) used to determine block position

Clamp Line Tensiometer (CLT) used to determine when
drillpipe goes into and out of slips.

Combination of above used to determine length
of pipe in the hole.

Checked against driller’s pipe tally every connection.

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MWD Depth Measurement

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LWD Measurements

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Resistivity Frequency Range

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Why 2MHz? Schlumberger Public

Induction-type LF measurement relies on cancellation of the direct
coupling (balanced arrays)
„ very sensitive to geometry, not suited to LWD (shock)

At 2MHz, phase-shift and attenuation can be
measured between two coils

Borehole compensation cancels differences between the two
receivers

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2 MHz Resistivity TheorySchlumberger Public

Current from Top Transmitter induces an
electromagnetic field within the formation. This
propagates away from the transmitter.

The wave induces a current at the receivers. The phase
and amplitude of the wave are measured and
converted to resistivity.

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Propagation Measurement

Transmitter EM-wave is attenuated in Schlumberger Public
conductive formations
Receiver
Receiver Near receiver
Far receiver
Transmitter
Finite propagation speed
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Emag Wave Geometry

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Equal phase lines Equal amplitude lines Schlumberger Public

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ARC475/Phasor induction DOI

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ARC475/Phasor induction

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DOI Considerations Schlumberger Public

2 Parameter Influencing DOI: Schlumberger Public

Distance from Transmitter to Receiver

• The greater the distance T/R the deeper the DOI

Signal frequency

• The lower the frequency the deeper the DOI

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