Schlumb_MWD LWD Basic

8/20/2019 Schlumb_MWD LWD Basic

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S ch l um b er g er P u b l i c


MWD and LWD Introduction

Graham Raeper

LWD Interpretation & Development

Schlumberger DCS Scandinavia


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© Schlumberger 2004

An asterisk is used throughout this presentation to denote a markof Schlumberger. Other company, product, and service names maybe trademarks, registered trademarks, or service marks of others.


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Measurement While Drilling Tools

– 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

•Jakosky patent, 1929

• Otis & Alder, 1955

First WL log (resistivity) 1927

SP 1931Induction 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

– 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 PrinciplesMudMud

Pressure

Time

Pressure

Time

MudMud

Pressure

Time

Pressure

Time

MudMudMud

Pressure

Time

Pressure

Time

Positive Pulse:1 BPS

Negative Pulse:

2 BPS

Continuous wave:

up to 12 Bits Per Second

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, andfinally 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...

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


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PowerPulse*

Impulse*

SlimPulse*

MWD Systems available in different sizes

Objective: MWD tools available today


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MWD Surveys Sensors

3 Accelerometers + 3 Magnetometers

Extender

Extender


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MWD Surveys Sensors

Sensor sets arranged orthogonally

Inclination Error:

- Movement

- Misalignment of the MWD

collar in the wellbore- Accelerometer misalignment

- Temperature

Azimuth Error:

- Magnetic parts

- LWD Power

- Collar Mass

- Collar Hot Spots


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UncertaintiesWell path is computed from surveys by minimum curvature method

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800

-600

-400

-200

0

200

400

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800

-600

-400

-200

0

200

400

Default Color

Main

Proposal

Survey

1600

1500

1400

1 3 0 0

1 2 0 0

A-3 H Plan

2 3 2 5

2 3 0 0

2 2 0 0

2 1 0 0

2 0 0

0

1 9 0 0

1 8 0 0

1 7 0 0

1 6 0 0

1 5 0 0

140 0

1300

A-2 H Pil ot Survey

2 1 7 7

2 1 7 7

2 1 0 0

2 0 0 0

1 9 0 0

A-2 AH Survey

2 1 0 0

2 0 0 0

1 9 0 0

1 8 0 0

1 7 0 0

1 6 0 0

A-1 H Survey

2 1 0 0

2 0 0 0

1 9 0 0

1 8 0 0

1 7 0 0

1 6 0 0

1 5 0

0

1 4 0 0

1 3

0 0

1 2 0 0

A4H Plan

SPIDER VIEW

Scal e (1 cm= 100 m)

< < <

S O U T H

N O R T H

> > >

>

Inclination accuracy: 0.1°

(FMI GPIT Incl. Acc. = 0.5°)

Azimuthal Accuracy: 1°

(FMI GPIT Az. Acc. = 2°)


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Link from MWD tool to LWD tools

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

Extender

Extender


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Logging While Drilling

The goal in developing LWD tools was to provide nearwireline quality measurements while drilling

Early MWD tools provided basic electrode (shortnormal) type resistivity & Gamma Ray measurements

2 MHz resistivity tools developed to obtain higherquality resistivity measurement in all mud types

Density/ Neutron measurement developed to provide

Triple Combo service – supports large percentage ofwells


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Triple Combo

Gamma Ray, Resistivity, Density, Pef, Neutron

• Providesmeasurements 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…

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

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

yes no

yes yes

Measurements Conveyance WL Conveyance LWD

Objective: High Service Quality


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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

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

Objective: Understand Demodulation

The Frame Display function is the parent application of SPM Demodulation. Thisapplication 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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(m/hr)

Increased rate of penetration

Telemetry is KeyDrilling Optimisation Data…

25

30

35

40

45

50

55

60

65

70

1500 2000 2500 3000 3500 4000 4500 5000

MD(ft)

I N C L

( d e g )

0

10

20

30

40

50

A Z I ( d e g

P W D C D & I S t i c k S l i p

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

Or 2.2 BPS log and a

Real-time density image

0.8 BPS


Real-time density image

0.8 BPS


Real-time resistivity

image

1.7 BPS


Real-time resistivity

image

1.7 BPS

Q C D a t a

H i g h R e s

A d v a n c e d L W

D


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Recording Mode Acquisition Rate

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)

ROP Communication with tool

to downlaod memory

Battery switch (LWD)


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Data vs Time -> Data vs Depth

+ Data vs Time = Data vs DepthDepth vs Time


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Time Based Data

Time to Depth Conversion

0.00 Gamma Ray 150.00

Depth Based Data

HOUR0.00 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).

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

Any changes in depth entered

by the engineer is reported

Depth Log / Tracking Sheet

Depth encoders


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Depth - What does the Client Want?

True Depth

Absolute Depth

Relative Depth

Reproducible Depth


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rue depth

Driller’s depth

Anadrill’s depth

at time t1

Anadrill’s depth

at time t2

Wireline depth,

attempt 1

Wireline depth,

attempt 2

Which Depth is That?

What is the depth of this formation top?


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LWD Depth vs Wireline Depth

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

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

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

It is a valid measurement, useful for

determining bed thicknesses and

geosteering applications

It is a valid measurement, useful for

determining bed thicknesses and

geosteering applications

•Additional errors are introduced whenmeasuring 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 truevertical depth.


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Summary of stretch calculations

Horizontal Well.

A well was analyzed using drilling engineering software. The well was vertical to 3000ft. 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

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?

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.

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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EM-wave is attenuated inconductive formations

Finite propagation speed

causes phase-differences

Propagation Measurement

Transmitter

Receiver

Receiver

Transmitter

Near receiver

Far receiver


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Emag Wave Geometry

Equal phase lines Equal amplitude 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:

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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400 KHz Measurement

Depth of investigation:

Deeper in conductive formations

Similar in resistive formations

Advantages:

Better signal in conductive formations (< 1 Ohm.m)

Less sensitive to eccentering

Limitation:

Less accurate at higher resistivity (low PS & ATT sensitivity toRt)


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Depth Of Investigation Comparison


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Blended (Best) Resistivity

Eccentering Effect

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.

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

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.

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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GVR Azimuthal Button Resistivity Measurements

GeoVISION Resistivity


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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

Caliper data can be acquired from several sources using LWD data.

• A real-time ultrasonic caliper is made with the Vision675 density tool• 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 ofbreakout along that plane

The caliper data can also be used to potential hazardous areas while tripping, running tubulars

or wireline


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Azimuthal Resistivity for Geological and Fracture Analysis

GVR and FMI Comparison

• Fracture presence and orientation are often key parameters to

drilling successful horizontal wells.

• This examples compares a wireline FMI Formation Micro-

Imager (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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Real Time Image Recorded Mode Image

GeoVISION Real Time Images

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

Wireline density tools typically use a skid mountedsource & detector to obtaingood contact with borehole

LWD tools use differentmethods to record densitydata with the loweststandoff as the tool rotates

Neutron porositymeasurements can becorrected for mud standoff


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Vision Azimuthal Density Neutron (VADN)

Density

Section

-C137 Gamma ray source

-Two gain-stabilized Nal

scintillation detectors

Neutron

Section

-AmBe neutron source-He3 detectors

-Thermal neutrons


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RHOb

Density Borehole Compensation

RHO ss

RHO ls

RHOmc

RHOmc < RHOb

DRHO > 0

RHOb = RHO ls + DRHO

DRHO = f (RHO ls - RHO ss)

“SPINE & RIBS” algorithm

compensates up to 1” stand-off

RHOmc > RHOb

DRHO < 0


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ADN Dual Source Assembly

Density Source

Neutron Source

Assembly


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CLAMP-ON STABILISER

BUILT-IN STABILISER


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ADN Images Theory

Azimuthal source and detectorszimuthal source and detectors

Quadrant arrays

uadrant arrays

Color

scale

Color

scale

ADN Density Image

DN Density Image


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Image Resolution

(Relative pixel sizes)

One inch

scale

Density

GVR

UBI

FMI

Pef

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.

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

6 i n

The sinusoids are not

resolved for apparent dips of

less than 35 Degrees

8.5 in

35°


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VADN Images

Ultrasonic

Pef

RHOS

RHOB (quad.) ROSI

RHOB (sect.) ROIM

RHOL

PowerDrive - 2D Images


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Comparison Real Time vs. Memory Image

RTI RMI


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LWD Calipers

Ultrasonic Caliper direct

Density CaliperPhase Caliper from Propagation Tool

Caliper from multiple DOI Resistivity

Neutron Caliper

Derived


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Ultrasonic Caliper Measurement

Borehole spiraling


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Factors that Affects Accuracy

Acoustic Impedance Contrast between Mud and Formation

Signal Attenuation in Heavy MudStandoff Range up to 2.5 in.

Hole Rugosity / Target Alignment

Advantages of the Ultrasonic Caliper

• Direct and Azimuthal Measurement

• Works in OBM and WBM

• Good Precision (0.1 –0.2 in.)

• Available in Real Time


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VADN/FMSImage Comparison

Drilling

down

sequence

parallel to

bedding

Drilling

down

sequence


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VADN

Density

Dynamic

Image

VADN

Pef

Dynamic

Image


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Azimuthal Density Reveals Filtrate DrapeAzimuthal Formation Evaluation - Gravity Segregation of Fluids

Gas

filtrate

• This is a quadrant density presentation from a horizontal well in a highpermeability 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

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”, whichis 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

Attenuator

Receivers

transmitter Receivers

Bottom Hole Assembly - ISONIC

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-timePorosity measurement

Lithology identification

Seismic correlation real-time input for synthetic seismograms

Pore pressure trends while drilling

Real-time decision making

Recorded modePorosity measurement

Lithology identification

Mechanical properties (hard rocks)

Improved quality sonic measurements Formation alteration (shales) & invasion

Hole enlargement

ISONIC Applications

ISONIC applications can be divided into two groups - real time and recorded modeapplications . Real time measurements provide the client with unique opportunities forbetter drilling decisions. The two main applications are real time seismic correlation andpore pressure indication.

Real Time Seismic Correlation

From real time ISONIC compressional slowness measurements, real time syntheticseismograms can be computed. These seismograms can be used to correlate the client’ssurface seismic data to driller’s depth. The client will learn where the bit is located on hisseismic section. This gives the client the opportunity to re-evaluate his drilling operationbefore he reaches total depth.

Pore Pressure Indication

In most sand/shale sequences, compaction increases with depth due to increasingoverburden with depth. Sound travels faster through sand/shale sequences the morecompacting occurs. Therefore, compressional delta-t lessens with depth at relativelyconstant rate. When overpressured formations occur, pore space is greater than normaland the delta-t value increases above the expected trend. Therefore, slow delta-t valuesabove the compacting trend indicate overpressured formations.

Recorded Mode

The major recorded mode application is wireline sonic replacement. Seismic tie andsonic porosity (computed from delta-t and used as an input to the petrophysicalevaluation (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 recordeddata. Combining shear with compressional slowness allows for mechanical propertycomputations such as IMPact*, MechPro* and Frachite*.

ISONIC compressional data is gathered well before wireline data can be acquired. Thismeans that the measurements are made before formation alteration, stress relief,invasion and increasing hole enlargement can occur. The result is that ISONIC slownessmeasurements may be a truer representation of the formation properties than subsequentwireline sonic measurements.


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The presence of drill collar requires an alternative tostandard 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

LWD Shear Measurement

in Slow Formations


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Dipole

Why Quadrupole?

Empty

borehole

Borehole

with collar

Quadrupole

Less sensitive

to shear

More sensitive

to shear

Strong collarinterference

Small collarinterference

Formation Shear

Formation Shear

Borehole mode

Borehole mode

Collar mode

Collar mode

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 shearlogging in slow formations in LWD environment.


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Seismic While Drilling Principle

Surface sourceDownhole receivers

Waveforms recorded in

downhole memory

Downhole processing

Real-time check-shot

via MWD telemetryLook-ahead imaging

seismic reflector

LWD Tool

sea floor M W D t e l e m e t r y

Source

Surface System


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SeismicVision System

Downhole Tool Surface System

Rugged LWD technology

Multiple sensors (3 Geophones, 1Hydrophone)

Processor, memory, telemetry

Triangular cluster (450 in3)

Bottled air supplySpecial control system

SPE71365

The SeismicMWD system has two main components, a downhole tool and

a surface system.

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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Wireline

Check shot data from Seismic While Drilling

First field test in Wyoming.

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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Pressure rampPressure ramp

Normally pressuredNormally pressuredclasticsclastics

ReservoirReservoir

20”

13 3 / 8”

9 5 / 8”

16”

11 3 / 4”

Example Exploration Well Plan

Now let’s imagine drilling an exploration well in a highly challenging

environment with the SeismicMWD tool.

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

Distance

to Target

Surface

Seismic

in Depth

Time-DepthCurve and

Depth

Prediction


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Bit On Seismic


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LWD-NMR

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 thanthe original tool. The tools currently being deployed are second generation tools.

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 tomeasure T2 (or T1)

in real time

Measurement

complicated

compared to

wireline by tool

motion


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LWD-NMR Outputs

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

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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Measurement & Motion

R e s o n a n t r e g i o n

Borehole Wall

ResonantRegion 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 90degreepulse, 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.

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 frequencyof 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

Bit Whir ling

&

Hole

Enlargement

0.1 cm

1.0 cm

Bit Whir ling

&

Hole

Enlargement

0.1 cm

1.0 cm

The above are examples of the kinds of whirling motion it is possible to resolve using the

tools capabilities.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 mudcake 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

Lateral motion leads to

shortening of T2’s

Effects Understood

Accelerometers lateral

motion velocity

QC from Accelerometry data.

QC from NMR data

Accelerometry Data Maximum Measurable T 2

Accelerometer Package is for QC Purposes

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 peakincreases 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

Measurementprinciple identical towireline formation pressuremeasurements

Rely on direct contact with theformation

Drill string movement must be stopped

A small area of the formation is sealedoff, and the pressure & mobility is tested

Dual packer type tools also existTool shown is not a Schlumberger tool

Draw Down Pump

Pressure Gauge

Sealing Element

System Volume


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GeoSteering -The full picture…

T T R

UDR Distance to boundary

GVR or VDN Real-Time Image

Vision Res. Medium DOI

Base Heimdal

BaseBalder

TopChalk

TopHeimdal

Base Heimdal

BaseBalder

TopChalk

TopHeimdal

Producers shall be drilled 9 m above

OWC or near base reservoir

Producers shall be drilled 9 m above

OWC or near base reservoir

Gas injectors shall bedrilled near top reservoir Gas injectors shall bedrilled near top reservoir


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Drilling Performance Sensors

VISION has a variety of Drilling performance sensors

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 LifeBHA whirling in vertical hole

Multi axis shocks

• Reduce drillstring fatigue

• Reduce borehole enlargement

• Increases ROP/bit life

Larger shocks result in more shock counts

All of Anadrill’s MWD and LWD tools are designed with downhole shock

measurements.

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

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.

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

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 MWDtool.

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 PDCbits 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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• Key for Deepwater drilling

• Detect shallow water flows

• Detect cuttings loading and swab/surge effects

• Manage the pore pressure fracture grad window

• Minimize mud weight for optimum ROP

Accurate control of ECDModeled vs. Actual ECD

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.

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

ISONIC example

taying within the pressure window

Left hand diagram: shows a real-time plot of the real-time ECD

measurement plotted against the theoretical fracture gradient and a real-

time 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.

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 transittime. 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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Shear Failure

Mud Weight too

Low

Tensile Failure

Mud Weight too

HighStress Direction

Identification of Failure Modes

LWD images can be acquired from both the GVR

(GeoVISION Resistivity) and ADN (vision density).

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 veryvaluable 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

MWD/ LWD has developed quickly compared to wireline technology

The technique is widely used in deviated wells and where rig ratesare high

In vertical wells and low rig day rates wireline is more economical– is there a need for RT data?

Almost all OH wireline measurements can be performed with LWD– fluid sampling and high definition images are the significant

measurements not yet available

DEPTH control is the biggest single quality factor thataffects LWD measurements

Schlumb_MWD LWD Basic

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