MWD LWD Basic

4/23/2004
Graham Raeper
Schlumberger Public
MWD and LWD Introduction
LWD Interpretation & Development
Schlumberger DCS Scandinavia
Schlumberger Public
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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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© Schlumberger 2004
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Measurement While Drilling Tools
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– 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
• Early Patents
First WL log (resistivity) 1927
SP 1931
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•Jakosky patent, 1929
• Otis & Alder, 1955
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
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– 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
Positive Pulse:
1 BPS
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Time
Mud
Pressure
Continuous wave:
up to 12 Bits Per Second
Time
Mud
Pressure
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Time
Starting with our telemetry, on this slide is represented the PowerPulse
series of MWD tools.
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Negative Pulse:
2 BPS
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
(Mud flow in the center of the tool for some LWD tools)
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MWD Systems available in different sizes
PowerPulse*
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Impulse*
SlimPulse*
Objective: MWD tools available today
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MWD Surveys Sensors
Extender
Extender
3 Magnetometers
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+
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3 Accelerometers
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MWD Surveys Sensors
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Azimuth Error:
- Magnetic parts
- LWD Power
- Collar Mass
- Collar Hot Spots
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Inclination Error:
- Movement
- Misalignment of the MWD
collar in the wellbore
- Accelerometer misalignment
- Temperature
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Sensor sets arranged orthogonally
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Uncertainties
Well path is computed from surveys by minimum curvature method
-1200
-1000
-800
-600
-400
-200
400
SPIDER VIEW
Scale (1 cm = 100 m)
A-1 H Survey
600
800
400
A-3 H Plan
1500
1400
1300
12
00
2100
200
1200
1400
1300
1600
1500
1600
1800
1700
1900
2000
77
21
0
1700
0
Azimuthal Accuracy: 1°
(FMI GPIT Az. Acc. = 2°)
-200
00
19
Default Color
Main
Proposal
Survey
A-2 H Pilot Survey
20
00
2325
2300
2200
210
0
2100
-400
-400
1300
00
20
1400
19
190
000
20
00
<<< SOUTH
00
21
1800
1500
1700
00
16
-600
-600
A4H Plan
-1000
-800
-600
<<< WEST
-400
-200
0
200
EAST >>>
400
600
800
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Inclination accuracy: 0.1°
(FMI GPIT Incl. Acc. = 0.5°)
1800
-200
200
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NORTH >>>
200
1600
A-2 AH Survey
400
0
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Link from MWD tool to LWD tools
Extender
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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Extender
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Logging While Drilling
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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
Gamma Ray, Resistivity, Density, Pef, Neutron
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• 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 LWD
yes
yes
yes
yes
no
16-bins
yes
yes
yes
no
5 outputs
20 outputs
5 outputs
5 outputs
12-bins
56-bins
yes
no
yes
yes
yes
yes
yes
yes
Yes
yes (memory only)
yes
yes
no
yes
yes
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Objective: High Service Quality
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Thermal Neutron Ø
Bulk Density
Azimuthal Density
Photoelectric factor
Spectroscopy / Sigma
Multi-depth Propagation R
Multi-depth Laterolog R
Azimuthal Resistivity
Micro-Resistivity Image
Compressional Dt
Shear Dt
Seismic Check shot
VSP
Formation Pressure
Fluid samples
NMR
Conveyance WL
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LWD Acquisition Workflow - Differences
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
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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
Principles
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:
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• 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
45
40
AZI (deg)
CD&I
INCL (deg)
PWD
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Slip
Stick
10
30
25
1500
2000
2500
3000
3500
4000
4500
0
5000
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(/m)
30
50
MD(ft)
Formation
Evaluation
Data…
1 bit per second
3 bits per second
6 bits per second
QC Da
ta
Or 2.2 BPS log and a
Real-time density image
Or 4.3 BPS log and a
Real-time resistivity
image
ced L
Advan
0.8 BPS
WD
1.7 BPS
(m/hr)
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es
High R
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Recording Mode Acquisition Rate
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To record 2 samples/ft
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)
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ROP Communication with tool
to downlaod memory
Battery switch (LWD)
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Data vs Time -> Data vs Depth
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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0.00
Gamma Ray
150.00
Gamma Ray
150.00
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Errors from Time/Depth merge
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).
„
The clocks might be incorrectly synchronized.
„
Clocks are not perfect, and will drift.
„
Clocks can “reset”, causing jumps.
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This can lead to additional errors due to the incorrect alignment of the two independently
recorded times:
Each of these effects cause unpredictable effects on the log.
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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
Any changes in depth entered
by the engineer is reported
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Depth encoders
Depth Log / Tracking Sheet
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Depth - What does the Client Want?
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True Depth
Absolute Depth
Relative Depth
Reproducible Depth
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Which Depth is That?
What is the depth of this formation top?
Wireline depth,
attempt 2
True depth
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Driller’s depth
Anadrill’s depth
at time t2
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Wireline depth,
attempt 1
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Anadrill’s depth
at time t1
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LWD Depth vs Wireline Depth
Wireline depth is the Geoscientist’s reference. Driller’s depth is
the Driller’s reference.
those corrections are difficult to apply, and are often
incomplete. The corrections are greater than the inaccuracy
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If Wireline depth is corrected properly, it is more accurate; but
of driller’s depth.
The industry does not want two different measurements of the
same thing. They want a repeatable measurement.
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Depth is our most important measurement.
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Depth Measurement
LWD’s depth is the driller's depth.
1. Difference between driller’s depth and true depth.
2. Difference between LWD’s measurement of depth and
driller’s depth
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There are 3 different areas that affect the accuracy of LWD depth (closeness to
true value):
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
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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•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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ItItisisaavalid
validmeasurement,
measurement,useful
usefulfor
for
determining
bed
thicknesses
and
determining bed thicknesses and
geosteering
geosteeringapplications
applications
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Summary of stretch calculations
Horizontal Well.
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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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.
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Difference between LWD’s measurement of
depth and driller’s depth
Draworks sensor, Geolograph and/or Rig Motion Sensor
Clamp Line Tensiometer (CLT) used to determine when
drillpipe goes into and out of slips.
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(RMS) used to determine block position
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?
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 Theory
Current from Top Transmitter induces an
electromagnetic field within the formation. This
propagates away from the transmitter.
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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
conductive formations
Near receiver
Receiver
Far receiver
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Receiver
Finite propagation speed
causes phase-differences
Transmitter
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Emag Wave Geometry
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Equal amplitude lines
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Equal phase lines
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ARC475/Phasor induction DOI
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ARC475/Phasor induction
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DOI Considerations
2 Parameter Influencing DOI:
• The greater the distance T/R the deeper the DOI
Signal frequency
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Distance from Transmitter to Receiver
• The lower the frequency the deeper the DOI
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400 KHz Measurement
Depth of investigation:
„
Deeper in conductive formations
„
Better signal in conductive formations (< 1 Ohm.m)
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Similar in resistive formations
Advantages:
„
Less sensitive to eccentering
Limitation:
„
„
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Less accurate at higher resistivity (low PS & ATT sensitivity to
Rt)
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Depth Of Investigation Comparison
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Blended (Best) Resistivity
Eccentering Effect
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2MgHz Phase Shift
400KHz Phase Shift
2MgHz Attenuation
400KHz Attenuation
Sorry about the quality-This log shows a log that has been severely affected by eccentering. 2-MHz tools are severely affected by
eccentering when there is a large Rt/Rm contrast or a large Rm/Rt contrast. In this case the blue curves in
track two are the 2-MHz phase shift outputs and the black curves in track three are the attenuation curves.
Both are affected by eccentering that has been exaggerated by a washout. In this case the environment
had a large Rm/Rt contrast (OBM and a Rt of less than 1 ohmm.
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One of the biggest advantages of the 400-kHz outputs is the immunity to eccentering. To take advantage
of the deeper reading 400-kHz at low resistivity and the immunity to eccentering as well as take advantage
of the higher signal to noise ratio and better vertical resolution of the 2-MHz a new output was created. It
is called the blended or best resistivity (P16B--Phase shift 16 -in spacing /blended output). The 400kHz
curve is presented below 1 ohmm, the 2MHz output is presented above 2 ohmm and the output is a
weighted average between 1 & 2 ohmm. This will be the standard presentation for the commercial version
of IDEAL 6.1 The blended outputs are the red and green curves. Note that they are very well behaved.
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Polarization Horn Effect
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Polarization Horn Effect
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VISION
Resistivity
vs. AIT
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The VISION resistivity log is extensively used for formation evaluation. It has a similar
response to the Array Induction Tool. Here five PS curves are plotted against the AIT. At low
resistivities, PS curves have about a one foot vertical resolution. The resolution is not
constant like the AIT, as the PS resolution degrades to 2 feet at 50 ohmms.
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The attenuation curve resolution is severely affected by an increase in resistivity. The
attenuation curve has a resolution of 2 feet at 1 ohmm but 8 feet at 50 ohmms.
The curve mnemonics are also different from that of an AIT.
For a VISION curve:
•1st letter denotes the curve--either P for Phase Shift or A for attenuation
•second two numbers represent the spacing (10,16,22,28,34, or 40 -inch)
•
Unlike the AIT this is not the constant depth of Investigation!!!
•The last letter is either “H” for High frequency (2-MHz) or “L” for low frequency (400-kHz)
Note that the IMPulse currently does not have the 400-kHz option but will be modified latter in
2000 that will provide it with increased memory to 50 MB, dual frequency, digital electronics
and simultaneous acquisition.
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GeoVISION Resistivity Tool
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GeoVISION Resistivity
GVR Azimuthal Button Resistivity Measurements
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GeoVISION Current Focusing
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Ring Resistivity Principle
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WL dual laterolog Resistivity response
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GVR focused Ring Resistivity response
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GRV Imaging: Break-outs and
Button Averaging
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GVR Azimuthal Caliper
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Caliper data can be acquired from several sources using LWD data.
• A real-time ultrasonic caliper is made with the Vision675 density tool
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• resistivity caliper from the CDR, ARC and RAB in WBM
Today the resistivity calipers are only available in memory but should be available in real-time
by the end of the year (99).
The caliper data provides a picture of the shape of the bore hole, indicating the severity of
formation breakout and the primary directions of failure
The diagram above shows caliper data from the Geovision resistivity tool at different depths,
highlighting that breakout has occurred long the north-west / south-east plane.
The resistivity image data from the same tool over the same interval clearly shows the areas of
breakout along that plane
The caliper data can also be used to potential hazardous areas while tripping, running tubulars
or wireline
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GVR and FMI Comparison
Azimuthal Resistivity for Geological and Fracture Analysis
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• Fracture presence and orientation are often key parameters to
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drilling successful horizontal wells.
• This examples compares a wireline FMI Formation MicroImager (left image) to a GeoVISION resistivity image (right
image) acquired during the drilling process.
• Note the fracture in the middle of each image. This sine wave
has a different orientation to the bedding planes.
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GeoVISION Real Time Images
Real Time Image
Recorded Mode Image
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70 ft
Ref.: SPE - 71331
This is an example of a compressed and decompressed image compared
to a recorded mode image straight from the tool memory (I.e. retrieved
when the tool was on the surface. Although the resolution of the
compressed and decompressed image is poorer the main feature of
cutting up through a thin conductive bed can clearly be seen.
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Density Neutron Measurement
LWD tools use different
methods to record density
data with the lowest
standoff as the tool rotates
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Wireline density tools
typically use a skid mounted
source & detector to obtain
good contact with borehole
Neutron porosity
measurements can be
corrected for mud standoff
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Vision Azimuthal Density Neutron (VADN)
-C137 Gamma ray source
Density Nal
-Two gain-stabilized
scintillationSection
detectors
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-AmBe neutron source
Neutron
-He3 detectors
Section
-Thermal neutrons
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Density Borehole Compensation
RHOmc < RHOb
DRHO > 0
RHOmc > RHOb
DRHO < 0
RHO ss
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RHO ls
RHOb = RHO ls + DRHO
DRHO = f (RHO ls - RHO ss)
RHOmc
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RHOb
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“SPINE & RIBS” algorithm
compensates up to 1” stand-off
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ADN Dual Source Assembly
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Assembly
Density Source
Neutron Source
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CLAMP-ON STABILISER
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BUILT-IN STABILISER
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ADN Images Theory
Azimuthal
Azimuthal source
source and
and detectors
detectors
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ADN
ADN Density
Density Image
Image
Color
Color
scale
scale
Quadrant
Quadrant arrays
arrays
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Image Resolution
(Relative pixel sizes)
Schlumberger Public
One inch
scale
Pef
GVR
UBI
FMI
Despite this coarseness of image, density images can prove invaluable.
They can be acquired in oil and water based muds. Using LWD allows
measurements in complex shaped wells that would require risky TLC runs
if they are possible at all.
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Density
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Furthermore many of these wells are logged at high angles, where even
thin bed are seen over many feet within the borehole.
As with any imaging tool a contrast in the medium being measured is
required to identify beds.
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Image resolution Limitation
35°
Schlumberger Public
™The sinusoids are not
resolved for apparent dips of
less than 35 Degrees
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6 in
8.5 in
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VADN Images
PowerDrive - 2D Images
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Ultrasonic
Pef
RHOS
RHOB (quad.) ROSI
RHOB (sect.) ROIM
RHOL
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Comparison Real Time vs. Memory Image
RTI
RMI
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LWD Calipers
Ultrasonic Caliper
direct
Density Caliper
Caliper from multiple DOI Resistivity
Neutron Caliper
Derived
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Phase Caliper from Propagation Tool
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Ultrasonic Caliper Measurement
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Borehole spiraling
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Advantages of the Ultrasonic Caliper
• Direct and Azimuthal Measurement
• Works in OBM and WBM
• Good Precision (0.1 –0.2 in.)
Factors that Affects Accuracy
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Acoustic Impedance Contrast between Mud and Formation
Signal Attenuation in Heavy Mud
Standoff Range up to 2.5 in.
Hole Rugosity / Target Alignment
Schlumberger Public
• Available in Real Time
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VADN/FMS
Image Comparison
Drilling
down
sequence
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parallel to
bedding
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Drilling
down
sequence
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VADN
Density
Dynamic
Image
Pef
Dynamic
Image
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VADN
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Azimuthal Density Reveals Filtrate Drape
Azimuthal Formation Evaluation - Gravity Segregation of Fluids
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Gas
filtrate
• This is a quadrant density presentation from a horizontal well in a high
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permeability gas zone.
• All quadrant densities (top, bottom, left and right) are “crossed-over” the neutron in
the characteristic gas signature.
• The quadrant densities themselves do not agree in the homogeneous formation.
The bottom density has the highest reading. The top density is the lightest.
• This is due to filtrate drape - gravity segregation to the bottom of the wellbore.
This generally occurs in high permeability gas zones due to the buoyancy force.
•Note the difference that this may make on resistivity measurements - GVR would
be useful in this case to compute quadrant water saturations.
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Azimuthal Porosity GeoSteering
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This example illustrates the benefit of azimuthal density geosteering. A gas zone is overlain by a shale. In
zone A, all four quadrants measure low densities and crossover the neutron, indicating a gas zone. The
top quadrant has a lower density than the bottom quadrant. This may be a result of “filtrate drape”, which
is gravity segregation of filtrate invasion toward the low side of this horizontal well.
The drillpipe is sliding for a short section, until zone B. The density measurement for the top of the
wellbore has increased as it is now measuring the shale bed above the wellbore. The other three
quadrants (bottom, left and right) still indicate gas. With the azimuthal measurement, you would now make
a decision to turn down, away from the shale boundary. However, with an average density, it may not
even be recognized that the wellbore was approaching a shale boundary.
The tool and drill pipe slides again to zone C. Now the wellbore is further into the shale section. Only the
bottom density indicates gas. Only now, would an average density reading indicate that a steering
decision would need to be made, but it still would not provide a direction.
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Sonic while drilling
transmitter
Receivers
Schlumberger Public
Receivers
Attenuator
Transmitter
Bottom Hole Assembly - ISONIC
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The ISONIC8 is combinable with any 8-in. LWD measuring device and is
traditionally run with LWD triple combo tools (e.g. CDR/RAB and CDN).
Similarly, the ISONIC6 can be run with all 6 3/4-in. collar LWD/MWD tools.
Both tools can be run with all bit types. Pictured is a typical quad-combo bottom
hole assembly. In such a configuration, the ADN/CDN will always be at the top
of the BHA to allow for source retrieval. The ISONIC would be typically next,
but it can be placed anywhere in the string, above or below the MWD tool, even
just above the bit in “low noise” environments (e.g. rotary drilling - not hard
rocks).
The ISONIC can be run with or without a downhole motor or geosteering
assembly.
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ISONIC-Array Sonic While Drilling
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Recorded Mode Data
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ISONIC Vs. Wireline Sonic
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Delta-T in Overpressure Zone
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ISONIC Applications
Real-time
Recorded mode
Schlumberger Public
Porosity measurement
Lithology identification
Seismic correlation real-time input for synthetic seismograms
Pore pressure trends while drilling
Real-time decision making
Porosity measurement
Lithology identification
Mechanical properties (hard rocks)
Improved quality sonic measurements
„
Formation alteration (shales) & invasion
Hole enlargement
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ISONIC Applications
Schlumberger Public
„
ISONIC applications can be divided into two groups - real time and recorded mode
applications . Real time measurements provide the client with unique opportunities for
better drilling decisions. The two main applications are real time seismic correlation and
pore pressure indication.
Real Time Seismic Correlation
From real time ISONIC compressional slowness measurements, real time synthetic
seismograms can be computed. These seismograms can be used to correlate the client’s
surface seismic data to driller’s depth. The client will learn where the bit is located on his
seismic section. This gives the client the opportunity to re-evaluate his drilling operation
before he reaches total depth.
Pore Pressure Indication
In most sand/shale sequences, compaction increases with depth due to increasing
overburden with depth. Sound travels faster through sand/shale sequences the more
compacting occurs. Therefore, compressional delta-t lessens with depth at relatively
constant rate. When overpressured formations occur, pore space is greater than normal
and the delta-t value increases above the expected trend. Therefore, slow delta-t values
above the compacting trend indicate overpressured formations.
Recorded Mode
The major recorded mode application is wireline sonic replacement. Seismic tie and
sonic porosity (computed from delta-t and used as an input to the petrophysical
evaluation (i.e. lithology, porosity, etc.) are the primary customer objectives for sonic data.
When running ISONIC in fast rocks, shear slowness can be acquired from the recorded
data. Combining shear with compressional slowness allows for mechanical property
computations such as IMPact*, MechPro* and Frachite*.
ISONIC compressional data is gathered well before wireline data can be acquired. This
means that the measurements are made before formation alteration, stress relief,
invasion and increasing hole enlargement can occur. The result is that ISONIC slowness
measurements may be a truer representation of the formation properties than subsequent
wireline sonic measurements.
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LWD Shear Measurement
in Slow Formations
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Schlumberger Public
The presence of drill collar requires an alternative to
standard wireline-like technology.
A Dipole measurement requires a very large
dispersion correction
R&D programs led to the starting of development
work in quadrupole technology for LWD
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Why Quadrupole?
Empty
borehole
Borehole
with collar
Dipole
Formation Shear
Strong collar
interference
Collar mode
More sensitive
to shear
Less sensitive
to shear
Schlumberger Public
Borehole mode
Borehole mode
Formation Shear
Quadrupole
Small collar
interference
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Shear slowness in slow formations is derived from the measurement of
dipole or quadrupole modes. Both of these modes are dispersive. They
propagate at the shear slowness at low frequencies. As the frequency gets
higher sensitivity to the shear slowness decrease and sensitivity to mud
slowness and other environmental parameters increase. Therefore, one
would like to make the measurement at as low frequency as possible.
However, for the dipole mode the presence of the drilling collar in the
borehole interferes with the formation dipole wave at the low frequencies
making it very difficult to extract formation shear information if at all
possible. The quadrupole collar mode on the other hand is cut-off at low
frequencies and interferes very little with the formation quadrupole wave.
In summary quadrupole measurement is much better suited to shear
logging in slow formations in LWD environment.
Schlumberger Public
Collar mode
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Seismic While Drilling Principle
Surface System
sea floor
LWD Tool
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seismic reflector
Surface source
Downhole receivers
Waveforms recorded in
downhole memory
Downhole processing
Real-time check-shot
via MWD telemetry
Look-ahead imaging
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MWD telemetry
Source
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SeismicVision System
Downhole Tool
Surface System
Schlumberger Public
Rugged LWD technology
Multiple sensors (3 Geophones, 1
Hydrophone)
Processor, memory, telemetry
Triangular cluster (450 in3)
Bottled air supply
Special control system
SPE71365
The SeismicMWD system has two main components, a downhole tool and
a surface system.
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The downhole tool was constructed of typical rugged LWD technology. It
was configured with multiple sensors including geophones, hydrophones
and accelerometers. In addition, it has a processor for downhole
computations, memory for storing data and a telemetry system for
transmitting data to the surface.
The surface system for these tests included a triangular airgun cluster with
a total volume of 450 cu in. A bottled air supply was used to reduce
maintenance for the long “while-drilling” operation. A specially developed
control system was used to activate the source in a manner that would be
synchronized with the downhole recordings.
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Check shot data from Seismic While Drilling
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Wireline
First field test in Wyoming.
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Traces in top section acquired while tripping down.
Bottom trace acquired while drilling at connection time.
Wireline VSP was run after the test. Very good match in
che-ckshot times.
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Applications
Real-time check-shot
Put the bit on seismic map
„
Update seismic velocities for PPP
„
Optimize ECD boundaries and drilling parameters
„
Update velocities for seismic reprocessing
Real-time salt proximity
Seismic look-ahead, 500+ ft (2003)
Replace intermediate wireline check-shot, save
rigtime
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Example Exploration Well Plan
20”
Schlumberger Public
16”
Normally pressured
clastics
13 3/8”
11 3/4”
Pressure ramp
9 5/8”
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Now let’s imagine drilling an exploration well in a highly challenging
environment with the SeismicMWD tool.
Schlumberger Public
Reservoir
The exploration basin is characterized by normally pressured clastics in
the shallow section, then a section with a severe pressure ramp and highly
over-pressured reservoirs.
To reach a deeper reservoir, the well must be geosteered accurately
through a step out section with an uncertain velocity profile.
To meet all of the objectives, wells in this region normally require flawless
planning, many casing strings and careful execution.
The well plan calls for a 20-, 13 3/8- and 9 5/8-in casing sequence and
contingent liners of 16 and 11 3/4-in. If needed, the contingent liners would
require underreaming and add considerable extra cost.
The key to success is to push the 20-in casing as deep as possible and to
set the 13 3/8-in casing exactly at the top of the pressure ramp that is an
obvious reflector on the surface seismic map but not easily recognizable
as a lithology change.
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Drilling Office - Bit on Seismic
Surface
Seismic
in Depth
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Time-Depth
Curve and
Depth
Prediction
Distance
to Target
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Bit On Seismic
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LWD-NMR
Schlumberger Public
This is a picture of the tool taken while testing at RMOTC (Rocky Mountain Oilfield Test Center) in June 1999
this is actually a picture of the first generation tool, but the second generation is essentially identical in the
antenna region shown here. The only difference is in the new tool has a longer section of slick drill collar than
the original tool. The tools currently being deployed are second generation tools.
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Describe picture
The spiral piece at the bottom is the field replaceable screw on stabilizer that is changed in the same way as a
drilling motor stabilizer.
Above this are antenna and wear bands.
The rest of the tool is slick.
Outline Presentation.
Questions rules (encourage interruption?)
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NMR While Drilling
Tools available to
measure T2 (or T1)
in real time
„
Measurement
complicated
compared to
wireline by tool
motion
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LWD-NMR Outputs
Schlumberger Public
Real Time Outputs
– Lithology Independent Porosity
– Bound Fluid Volume (BFV) / Free Fluid Volume (FFV)
– T2LM (Log mean of T2)
– Permeability
– Hydrocarbon from Multi-Wait Time Porosities
Additional Outputs from Recorded Mode
– Raw Echoes
– Full Data Re-Processing
– Full T2 Spectra
– Motion Data
LWD-NMR Outputs
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The tool performs downhole a T2 inversion and computes outputs for transmission in real
time. These real-time outputs could be used for GeoSteering, well placement, sidetrack
decisions, etc….
Direct hydrocarbon identification using porosities from multiple polarization times (examples
shown later) (see FAQ’s for description of hydrocarbon identification/characterization
methods)
Permeability is calculated uphole from the bound fluid free-fluid ratio using Coates-Timur
equation or from the SDR equation if T2LM is transmitted, coefficients and exponents for
these equations can be set by the user at the wellsite based on client desires.
The tool records the raw echoes and this data can be used to reprocess the data in the
IDEAL wellsite software. A more detailed (more components in T2 spectrum) can be
computed from the raw data. In addition, the tool records full accelerometer and
magnetometer data whose primary purpose is for QC of NMR data, but some interesting
drilling engineering applications will also be shown.
------------------------------Note that the downhole memory of the tool is obviously not unlimited. No “maximum footage
loggable” specification can be given as the tool records verses time. Currently the tool can
record around 104 megabytes of memory. Note that the tool only records while circulating.
Prior to the job during the planning stage the memory can be set up to record for longer
periods of time by stackking the raw echoes. As NMR data is inherently statistical and when
reprocessed the echoes are stacked anyway, there is no significant loss of information. In
this way, the memory can be programmed to last as long as required.
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Resonant region
Measurement & Motion
Borehole Wall
Resonant
Region
Experiment
Region
The slide above shows the tool at first centered in the borehole at the beginning of
the measurement cycle. An experiment region is established with the 90degree
pulse, the 180 pulse should then be performed with a coincident resonant zone, i.e.
the tool should not move. The diagram on the right shows how the resonant region
stays at a fixed radius around the tool but the experiment zone is fixed in the
formation. In other words the experiment is now in error due to movement.
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This is clearly a very great challenge with the drilling environment, either the
experiment has to be fast compared to the motion and or the tool should be
stabilized to reduce motion.
Also the slide demonstrates where the measurement is made. In a cylinder of a
particular thickness around the tool. It is where the magnetic field and the frequency
of the radio signal combine to produce a resonant effect in the hydrogen nuclei, this
is how only hydrogen is measured in the experiment. And also that no signal is
received from in front of or behind the resonant zone. In other words there is a well
defined and constant measurement region from this tool unlike other nuclear or
resistivity tools.
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Drilling Dynamics From Accelerometry
0.1 cm
Schlumberger Public
Bit Whirling
&
Hole
Enlargement
1.0 cm
The above are examples of the kinds of whirling motion it is possible to resolve using the
tools capabilities.
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Each graph shows the locus of lateral movement of the center of the tool, as it moves in the
bore hole. The scale is in meters, top left shows millimeter size whirl, top right sub millimeter
and bottom left shows centimeter range movement of about an inch that was constrained by
the tool hitting the borehole wall.
These motions are more or less damaging according to their shape and frequency of
oscillation. The lower left hand one may be particularly damaging as the oscillations are
much larger amplitude (6-7 cm) and the BHA is whirling around the outside of the borehole
contributing to borehole enlargement and possibly damaging formation by compressing mud
cake into the formation.
------------------------------------------------------------------------These were all recorded in one bit run in a shallow vertical hole with a rock bit at 500 ft/hr and
80-150 rpm parameters.
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Quality Control of Motion Effects
Schlumberger Public
Lateral motion leads to
shortening of T2’s
Effects Understood
Accelerometers Æ lateral
motion velocity
QC from Accelerometry data.
QC from NMR data
Accelerometry Data Æ Maximum Measurable T2
Accelerometer Package is for QC Purposes
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The motion data can be used for quality control of the log in recorded mode or real-time by
utilizing the lateral velocity of the tool, to compute the maximum T2 that can be resolved.
This is an example drilling through a gas sand. From the accelerometry package we can
calculate an average lateral velocity shown in track 1. This leads to the red line in the T2 track
that shows the limit of the T2 that could be resolved under the motion conditions experienced
by the tool while the measurements are made. You can see that the transition from shale to
the shaley gas sand sees the appearance of a second T2 peak that is to the left of the T2
maximum line. A separation from the line of about a decade indicates that there is probably
little or no motion shortening of the T2. Further down in the slightly better pay the T2 peak
increases in time to the right but is still to the left of the line so is certainly not noise, but
because it is a little closer to the line it will be somewhat shortened due to tool motion.
NMR standalone QC is also being investigated by looking only at the NMR data and
determining motion effects by looking at the NMR data itself.
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Formation Pressure While Drilling
„
„
„
„
Draw Down Pump
Pressure Gauge
Sealing Element
System Volume
Schlumberger Public
„
Measurement
principle identical to
wireline formation pressure
measurements
Rely on direct contact with the
formation
Drill string movement must be stopped
A small area of the formation is sealed
off, and the pressure & mobility is tested
Dual packer type tools also exist
Tool shown is not a Schlumberger tool
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GeoSteering -The full picture…
UDR Distance to boundary
Schlumberger Public
Vision Res. Medium DOI
T
T
R
Base Balder
GVR or VDN Real-Time Image
Gas injectors shall be
drilled near top reservoir
Top Heimdal
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Top Chalk
Schlumberger Public
Base Heimdal
Producers shall be drilled 9 m above
OWC or near base reservoir
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Drilling Performance Sensors
Schlumberger Public
VISION has a variety of Drilling performance sensors
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Downhole weight, torque and multi-axis vibrations are not available on
VISION475.
PERFORM is a service which provides a Specialist Engineer who uses the
drilling performance sensors, surface indicators, offset well data,
knowledge database and local knowledge to improve the drilling process
to identify and reduce risk as well as improve overall ROP.
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Increase Drillstring and Bit Life
BHA whirling in vertical hole
Multi axis shocks
• Reduce drillstring fatigue
• Reduce borehole enlargement
• Increases ROP/bit life
Schlumberger Public
Larger shocks result in more shock counts
All of Anadrill’s MWD and LWD tools are designed with downhole shock
measurements.
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In the MWD tools shock data is transmitted in real-time such that in the
event of high shocks drilling parameters can be adjusted and the effects
monitored.
Real-time shocks can reduce non productive time, as trips can be saved
by:
• reducing pipe fatigue
• failure of downhole components
• increasing bit life.
Multi axis shock measurements are also available (ie. Axial, lateral and
torsional) With this information it is possible to determine the type of
vibrations experienced (e.g. bit bounce, stick slip, resonance etc.) and
thus take appropriate action
The shock measurements are alsoused to track wear and tear on the tools
and the level of maintenance required on a tool is based upon the severity
of shocks experienced.
It should be noted that although the MWD/LWD electronics are the most
susceptible damage from shocks, failure of these components is not
catastrophic. Where as the effect of high shocks on BHA connections can
lead to catastrophic failures.
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Early Washout Detection
BHA whirling in vertical hole
Schlumberger Public
Output Voltage vs. Flow Rate for 8-in. Turbine
The PowerPulse/Impulse MWD system uses a downhole turbine to
generate power. The output voltage from this turbine is directly
proportional to the flow rate passing through the tool and is thus a valuable
downhole flow meter which is sensitive to very small changes in flow.
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As the example shows, any washout above the MWD tool is easily seen
from the turbine voltage, a lot earlier than it is seen at surface. Early
identification can help reduce non productive time for expensive fishing
trips. This can be set up as a smart alarm on the IDEAL system, thus
requiring no continuous interpretation of the data by the engineer.
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Stuck Pipe Avoidance
Schlumberger Public
Weight on Bit
Torque
The PowerPulse tool can be configured to provide real-time
measurements of downhole weight on bit and torque. These
measurements are made based on strain gauges mounted in the MWD
tool.
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The gauges for the weight on bit are aligned so that they are only sensitive
to the axial load (tension and compression on the drillstring). The torque
gauges are aligned so that they are only sensitive to the torsional effects
on the drillstring (I..e. not the axial forces)
These measurements are particularly valuable in deviated wells where
surface parameters of weight and torque can be unrepresentative of the
true downhole conditions. By using the downhole measurements the
performance of the bit can be optimized and premature damage of PDC
bits avoided.
By comparing both surface and downhole parameters a calculation of the
friction in the wellbore can be made and the onset of pipe.sticking
detected and action taken
The example shows how the sliding friction (drag) is increasing, indicating
the onset of a potential sticking problem. A wiper trip was made and the
log shows the impact of the corrective action. In this case it was
successful and drilling was resumed.
Thus using these measurements NPT an be reduced by optimizing bit
performance and avoiding stuck pipe.
The calculated friction factors are also a valuable input into the planning of
the next well.
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Accurate control of ECD
Modeled vs. Actual ECD
Schlumberger Public
• Key for Deepwater drilling
Anadrill can provide real-time annular pressure measurements in each
hole size. This measurement is used to calculate the true ECD (effective
circulating density) while drilling to ensure that the ECD remains higher
than the formation pore pressure, yet lower than the fracture gradient of
the formation.
Schlumberger Public
• Detect shallow water flows
• Detect cuttings loading and swab/surge effects
• Manage the pore pressure fracture grad window
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• Minimize mud weight for optimum ROP
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Right hand diagram: shows the theoretical ECD (black). Without
downhole measurements this is the value used to define the mud weight
required to drill the well. The red curve shows the actual ECD as
measured by the downhole sensor and shows that there are major
fluctuations, compared to the modeled value, as a result of changing flow
rate and RPM. Other key factors that can effect the ECD are cuttings
loading pipe eccentricity, swab surge effects and temp/pressure effects. It
is clear therefore that in a well where there is a tight window between the
formation pore pressure and the fracture gradient to rely on a modeled
ECD value is dangerous and that real-time monitoring is crucial. This is
particularly true in the case of deepwater drilling where there can be a very
narrow window.
The ECD can also be calculated there is no circulation for accurate leak
off/formation integrity test measurements and to monitor swab/surge
effects
The APWD measurement has also proven to be a valuable tool for the
early detection of shallow water flows (a sharp increase is seen)
All annular pressure measurement can also be stored in the tools
downhole memory.
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Staying within the Pressure Window
Staying within the pressure window
ISONIC example
Schlumberger Public
Left hand diagram: shows a real-time plot of the real-time ECD
measurement plotted against the theoretical fracture gradient and a realtime calculation of pore pressure based on LWD resistivity. The pore
pressure calculation is compared to the seismic pore pressure calculation
that was made prior to drilling the well.
Schlumberger Public
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Accurate monitoring of both the pore pressure and ECD are key. This is
particularly the case in deepwater wells were the window between fracture
gradient and pore pressure can be very narrow.
Right hand diagram:shows an example of how LWD sonic data can also
be used for real-time pore pressure evaluation. The normal compaction
trend of the formation would result in a gradual decrease in sonic transit
time. However, in overpressured formations we see that the formation
becomes less compacted and the sonic transit time diverges from its
normal trend and increases as a function of over pressure.
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Identification of Failure Modes
Shear Failure
Mud Weight too
Low
Schlumberger Public
Tensile Failure
Mud Weight too
High
Stress Direction
LWD images can be acquired from both the GVR
(GeoVISION Resistivity) and ADN (vision density).
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As well as clearly showing the interbedding of the
formations and the dip of the beds, these images can
be used to define fractures. Both the direction of the
fractures and the failure mode can be determined.
When combined with Real time images, this will be very
valuable in refining or confirming wellbore stability
models and drilling practices.
But in the above example, the explanation shows that
the mud weight is too high AND too low. How can this
be--which is it?
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Conclusion
– is there a need for RT data?
Schlumberger Public
MWD/ LWD has developed quickly compared to wireline
technology
The technique is widely used in deviated wells and where rig rates
are high
In vertical wells and low rig day rates wireline is more economical
Almost all OH wireline measurements can be performed with LWD
– fluid sampling and high definition images are the significant
measurements not yet available
119 GR
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Schlumberger Public
DEPTH control is the biggest single quality factor that
affects LWD measurements
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