Sonic Scanner Br.ashx Slb Article

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Acoustic

scanning

platform

Sonic Scanner



Adding radius to borehole acoustics

For decades, the oil and gas industry

has used borehole acoustic measurements

throughout the lifecycle of wells to evaluate

rock properties in the near-wellbore region.

As the industry continues to develop new

methods for producing hydrocarbons

more efficiently, a focus on well integrity

has become ever more important.

Schlumberger has designed a tool usingthe latest acoustic technology for advanced

acoustic acquisition, including cross-dipole

and multispaced-monopole measurements.

In addition to axial and azimuthal measure-

ments, the tool makes a radial measurement

to probe the formation for near-wellbore

slowness and far-field slowness. Typical

depths of investigation equal two to three

times the borehole diameter.

The new Sonic Scanner* acoustic scan-

ning platform provides advanced types of

acoustic measurements, including borehole-

compensated monopole with long and shortspacings, cross-dipole, and cement bond

quality. These measurements are then con-

verted into useful information about the

drilling environment and the reservoir,

which assists in making decisions that

reduce overall drilling costs, improve

recovery, and maximize productivity. The

following field examples demonstrate the

greater flexibility in acoustic measurements

offered by the Sonic Scanner tool.

Achieving a better understandingof acoustic propagation

To enable a deeper understanding of

acoustic behavior in and around the bore-

hole, the Sonic Scanner tool allows accu-

rate radial and axial measurements of the

stress-dependent properties of rocks near

the wellbore. The Sonic Scanner platform

provides multiple depths of investigation,

excellent waveform quality, and presenta-

tions that reduce the complexity of sonic

logging, without compromising the depth

of information.

The more comprehensive understanding

obtained by using the Sonic Scanner plat-form helps to improve fracture planning,

sand control, and perforating design.

Overcoming earlier acousticmeasurement barriers

Regardless of the formation type, the

Sonic Scanner platform design overcomes

earlier acoustic measurement barriers to

successful formation characterization and

quantification because it■ uses a wide-frequency range that

enables characterizing formations as

● homogeneous or inhomogeneous

● isotropic or anisotropic

■ uses long- and short-monopole

transmitter-receiver spacing

■ is fully characterized with predictable

acoustics.

Earlier technologies attempted to operate

close to the tool’s low-frequency limit, or

they depended on previously acquired

formation information to anticipate forma-

tion slowness prior to data evaluation.

The wide-frequency spectrum used by

the Sonic Scanner tool allows data captureat high signal-to-noise ratios and extracts

maximum data from the formation. This

design feature also helps ensure that data

are acquired regardless of the formation

slowness. The monopole transmitters have

Figure 1. The Sonic Scanner tool provides the bene-fits of axial, azimuthal, and radial information from both the monopole and the dipole measurements for near-wellbore and far-field slowness information.

Applications

■ Geophysics

● Improve 3D seismic analysis

and seismic tie-ins

● Determine shear anisotropy

● Input to fluid substitution

■ Geomechanics

● Analyze rock mechanics

● Identify stress regimes

● Determine pore pressure

● Evaluate well placement

and stability

■ Reservoir characterization

● Identify gas zones

● Measure mobility

● Identify open fractures

● Maximize selective perfo-

rating for sand control

● Maximize safety window

for drawdown pressure

● Optimize hydraulic fracturing

■ Well integrity

● Evaluate cement bond quality

Benefits

■ Enhance hydrocarbon recovery

■ Make real-time decisions with

real-time quality control

■ Improve reserves estimates

■ Decrease operating time and

reduce job costs by eliminat-ing multiple logging runs

■ Reduce uncertainty and

operating risk

Features

■ Robust measurement of

compressional and shear

slownesses

■ Increased logging speed

(1,097 m/h [3,600 ft/h])

■ Multiple monopole transmitter

and receiver spacing

■ High-fidelity wideband wave-

forms and dispersion curves

■ Large receiver array

■ Predictable acoustics

■ Enhanced behind-casing

measurements with simulta-

neous cement bond log (CBL)

and Variable Density* cement

bond quality measurements

■ Extremely rugged electronic

package



enhanced low-frequency output over the

entire range of sonic frequencies; and

the dipole transmitters are designed for

high-output power, high-purity acoustic

waves, wide bandwidth, and low power

consumption.

The Sonic Scanner receivers feature a

longer azimuthal array than other acoustic

tools; i.e., 13 stations and 8 azimuthal

receivers at each station. With the twonear-monopole transmitters straddling

this array and a third transmitter farther

away, the short- to long-monopole trans-

mitter-to-receiver spacing combination

allows the altered zone to be seen and

provides a radial monopole profile.

Seeing beyond the altered zone

The long-spaced transmitter-to-receiver

concept in earlier acoustic tools was

designed for “seeing” past the altered

zone and attempted to provide an unal-

tered slowness measurement.The range of Sonic Scanner transmitter-

to-receiver spacings is both short and

long enough to see the altered zone and

thus provide a radial monopole profile.

These features improve measurement

accuracy of the fluids and the stress-

dependent properties of the rocks near

the wellbore; and that benefits fracture

planning, sand control, and perforating

design, as well as shallow-reading-device

point selection.

The wide-frequency spectrum from

the dipole transmitters used in the SonicScanner platform eliminates the need for

multiple logging passes that were common

with the earlier-generation acoustic tools.

New telemetry, optimized with software

and hardware, enables increased logging

speeds and decreased operating times.

Obtaining well integrity measurementswith high accuracy

The Sonic Scanner tool provides a dis-

criminated cement bond log (DCBL) that

can be obtained simultaneously with the

behind-casing acoustic measurements.

The two monopole transmitters positioned

at either end of the Sonic Scanner tool

allow 3-ft and 5-ft cement bond log (CBL)

and cement bond quality measurementsthat are independent of fluid and tempera-

ture effects and do not require calibration.

To demonstrate the DCBL measure-

ment accuracy, a logging run made with

a Sonic Scanner tool is compared with

measurements from a CBT* Cement

Bond Tool. The DCBL measurements are

indicated in blue and the CBT measure-

ments are in black. A very good match

is shown between the measurements

of the CBT tool and the azimuthally

averaged Sonic Scanner platform.

The transit time scattering shows ±0.31-in

eccentering in the 7-in, 23-lbm/ft casing.

The two bond index measurements

show good agreement, even in the zone

of high eccentralization near the top of

the interval.

Removing uncertainties about formation

geometry and structure

A recurring problem encountered inreservoir modeling and simulation is the

lack of available image data having a fine

scale. Until now, the only available alter-

natives have been to work with surface

seismic data, often too coarse in quality,

or near-wellbore imaging and its associ-

ated limitations. Coupled with the scale

of seismic measurements, additional

uncertainties arise regarding geometry

and structure, formation property varia-

tion, and fluid movements.

GammaRay

Depth,

ft

gAPI

0 150 0 150 0 1 200 1200275 295 200 600 0 50

dB/ft mV

XX,700

XX,800

XX,900

XY,000

XY,100

XY,200

XY,300

XY,400

Variable

Density

Variable

Density

Discriminated

Attenuation

Variable

Density

Discriminated

Amplitude

VariableDensity*

Bond

Index

Transit

Time

Sonic Scanner

Bond index limit

CBT

Sonic Scanner

Figure 2. A very good match is shown between azimuthally averaged Sonic Scanner platform and C BT curves (1). C urve scattering indicates 0.31-in eccentering (10 % of the internal radius) in the 7-in casing (2).A good match between bond index measurements is indicated (3).

1

2

3



The inset image in Fig. 3 shows the

surface seismic data with normal, rather

poor, resolution. In the Sonic Scanner

image of Fig. 3, the solid green line indi-

cates the interpreted reservoir top, and

the dashed blue line is the interpreted

bottom of the main sand body. The purple

line shows the wellbore path.

The relative horizontal position along

the bottom scale is 20–600 m from left

to right, and the vertical scale (deep

reading) is in increments of 5 m, show-

ing clearly more than 15 m of excellent

resolution compared with the surface

seismic image.

The Sonic Scanner image measurements

are used to update the geological model

and as input to the reservoir simulator

for predicting pressure with production.

Obtaining transversely isotropicformation parameters

A 3D anisotropy algorithm transforms the

compressional, fast-shear, slow-shear, and

Stoneley slowness Sonic Scanner meas-

urements with respect to the borehole

axes to anisotropic moduli referenced to

the earth’s anisotropy axes. These moduli

help to classify formation anisotropy into

isotropic, transversely isotropic (TI), or

orthorhombic types. The moduli also

assist in identifying microlayering or

thin-bedding-induced TI anisotropy

(N < 0 implies microlayering-induced

Trueverticaldepth,

m

XX,000

XX,005

XX,010

XX,015

XX,020

20 600

Horizontal position, m

Figure 3. Excellent resolution obtained from the Sonic Scanner tool compared with the surface seismic image.

Thin BedDepth

m

XX,800

XY,000

XY,200

XY,400

XY,600

XY,800

Shale

N_TIV@3D_Aniso_Com

GPa–300 300

Borehole Deviationdeg0 90

Fast Shear DT

µs/ft440 40

Compressional DTµs/ft440 40

S toneley DT

µs/ft440 40

Slow Shear DT

µs/ft440 40

GPa0 10

GPa0 10

GPa0 10

GPa

GPa0 5

0 5

Shear Rigidity inX2–X3 Transversely

Isotropic Ver tical Plane

Shear Rigidity in

X1–X2 Transversely

Isotropic Ver tical Plane

Shear Rigidity inX2–X3, X1–X2, and

X1–X3 Borehole Plane

Shear Rigidity in

X2–X3 Transversely

Borehole Plane

Equivalent Shear

Rigidity in

Borehole Plane

Figure 4. In this example, the high-gamma ray activity indicates a shaly interval. An isotropic zone (N = 0) extends from XY,500 to XY,600 m, and a high-permeability zone exists from XY,005 to XY,100 m.

Top of reservoir

Bottom of main sand body

Wellbore

Interpreted oil /gas contact

Isotropic

Highpermeability

Drilled well

Planned well



intrinsic anisotropy; N > 0 implies bedding-

induced anisotropy), relative magnitude

of principal stresses, and fluid mobility

in porous rocks.

Figure 4 shows the 3D anisotropy algo-

rithm’s ability to generate the TI param-

eters. With reference to a borehole that

is parallel to the X3 axis, shear modulus

or rigidity in the X2-X3 plane and shear

rigidity in the X1-X2 plane enablequicklook interpretation of formation

anisotropy, stress, and mobility effects.

Determining formation mobility

Because there is essentially no continuous

logging measurement of mobility available,

other methods have to be considered.

One method is to measure formation

mobility, which is the ratio of perme-

ability to viscosity.

Mobility, however, is not always avail-

able when it is needed because porosity

estimates are often preliminary, wirelinecores require an additional run into the

well, and whole cores are expensive.

When the borehole is in reasonably

good condition, Stoneley waves can be

used to measure a continuous mobility

profile in sands and carbonates. These

data can serve as an extension of core

permeability over a continuous interval

to save on coring costs, or to get a quick

permeability estimate for selecting the

perforating interval.

Minimizing the effects of tool presence

on sensitive Stoneley wave measurements

is extremely important. The design of the

Sonic Scanner tool, coupled with exten-

sive laboratory and field testing, enables

highly accurate prediction of the effects

of the tool on acoustic measurements

in all environments.

The example in Fig. 5 demonstrates

how the Sonic Scanner Stoneley waves

can be used to measure a continuous

mobility profile and obtain a quick per-

meability estimate. Other applications of

Stoneley permeability include formation

evaluation, production testing strategy

and programs, and reservoir modeling.

Evaluating the mechanical propertiesof formations

Acoustic measurements have typically

been acquired in 1D as a function of

depth, but seldom in 2D simultaneously

as a function of depth and azimuthal

direction. And interpretation has almost

always been based on the assumption

that the formations were homogeneous

and isotropic—a debatable assumption,

0 100

240 40

300 200

160 60

Porosity

gAPI

%

in

g/cm3

Gamma Ray

QualityFlag

X,X20

X,X40

X,X60

Caliper

Signal- to-Noise

Ratio

DepthBulk Density

0 150

30 dB 50

ft

6 16

1.95 2.95

DT Compressional

µs/ft

µs/ft

µs/ft

µs/ft

DT Shear

DT S toneley

DT mud0 16,000µs/ft

Sonic Scanner S toneley1 10,000

1 10,000

Sand

Coal

Water

Bound Water

Oil

mD/cP

mD/cP

S toneley Mobility

Mobility Error

MDT Mobility

Shale

300 150

X,X00

Figure 5. Mobility measured by the Sonic Scanner tool is shown in Track 4. The red dots indicate mobility values measured by the MDT * Modular Formation Dynamics Tester, which show good agreement.



at best, because of fracture alignment,

dipping beds, unbalanced stresses, and

formation damage from drilling.

The Sonic Scanner tool enables a full

3D characterization of the formation by

adding the radial dimension from the

multiple transmitter-receiver spacings,

along with wideband frequency measure-

ments and acquisition of all acoustic

modes propagating in the borehole. Fromthe expanded set of measurements, dom-

inant formation data can be evaluated

and the appropriate processing tech-

niques can be selected to extract 3D

acoustical properties.

In a tight-gas reservoir, formation

evaluation data and wellbore images

were combined with Sonic Scanner

shear wave anisotropy and Stoneley

wave data shown in Fig. 6. Wellbore

stability simulation was used to ensure

consistency between the mechanical

earth model and the logging and drilling

data. The mechanical earth model was

then applied to optimize subsequent

drilling operations.

Detecting and evaluating open

fractured intervals

Understanding the mechanisms of aniso-

tropy can be important when selecting

the right hydraulic fracture fluid for a

well, especially if there is stress-induced

anisotropy or intrinsic anisotropy related

to the presence of natural fractures. The

Sonic Scanner tool can be used in evalu-ating the type of anisotropy, in addition

to differentiating between open natural

fractures and drilling-induced fractures.

The fractures shown in the FMI*

Fullbore Formation MicroImager log

in Fig. 7 are near vertical. Upon foot-

by-foot examination, they were origi-

nally interpreted to be drilling induced.

Stoneley wave measurements from the

Sonic Scanner tool made it clear that the

fractures were open natural fractures

and not drilling induced.

The additional sonic data undoubtedly

prevented the operator from making an

incorrect interpretation, which would

have led to selection of a high-gel fracture

fluid that would have destroyed the

permeability of the naturally fractured

formation. In this situation, encapsulated

breakers are much less effective, and an

effective treatment can be designed.

In addition to preventing fluid loss,

this information would also be critical

in preventing cement loss during com-

pletion operations.

WashoutCrossline

Energy

MaximumCrossline

Energy

MinimumCrossline

Energy

Gamma Ray

Bit Size

Caliper 1

Depth

XX,050

XX,100

ft

Caliper 2

S toneley Frac tures

0 gAPI 150

4 in 14

4 in 14

0 100

0 100

Fast-In-LineVariableDensity

Slow-In-LineVariableDensity

0 µs 6,000 0 µs 100

DT Shear Fast DT Shear Fast DT Shear Slow DT Shear Slow

80 µs/f t 280

SlownessProjec tion

SlownessFrequencyAnalysis

SlownessProjec tion

SlownessFrequencyAnalysis

80 µs/f t 280

80 µs/f t 280

80 µs/f t 280

80 µs/f t 280

80 µs/f t 280

80 µs/f t 280

R es is tiv e C on duc tive

FMI Image

Dynamic ImageHorizontal Scale: 1:13.744

Orientation Nor th

80 µs/f t 280 0 120 240 3604 in 14

0 in 0.5

Figure 7. Stoneley wave measurements enabled determination that the fractures were natural, not drilling induced.

Young’sModulus

Earth Stress Plo

FMI log

t

Pore pressure

σmax Shale

σmax Sand

σmax Sand-Wbs

σmin Sand

σmin Sand-Wbs

σmax Shale-Wbs

σVertical

σmin Shale-Wbs

σmin Shale

Mud loss DataFRAC* service

Kick Pressure Xpress*service

Delta Stability

E f f e c t i v e

a x i a l s t r e s s ,

p s i

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Axial strain, %

6 8 10 12 14 16 18 20 22

Equivalent mud density, ppg

-10 -5 0 5 10

Distance, in

D i s t a n c e

( i n )

x10

o3

= 3000psi

Sample 67-S1Depth: 4912.00ft

2.5

2

1.5

1

0.5

0

0

2,000

4,000True

verticaldepth,

ft 6,000

8,000

10,000

10

5

0

-5

-10

E- 3 .084x10 ps i

Figure 6. A mechanical earth model can be constructed and compared with independent measurements of rock properties and in situ stresses.



05-FE-130 © 2005 Schlumberger

November 2005 *Mark of Schlumberger

Produced by Schlumberger Marketing Communications

www.slb.com/oilfield

Sonic Scanner Measurement Specifications

Output Compressional and shear DT, full waveforms, cement bond quality waveforms

Max. logging speed 1,097 m/h [3,600 ft/h]†

Range of measurement Standard shear slowness: <4,921 µs/m [1,500 µs/ft]

Vertical resolution <1.82-m [6-ft] processing resolution for 15.24-cm [6-in] sampling rate‡

Accuracy DT: <6.56 µs/m [2 µs/ft] or 2% up to 35.6-cm [14-in] hole size<16.40 µs/m [5 µs/ft] or 5% for >35.6-cm [14-in] hole size

Mud weight or type limits None

Combinability Fully combinable with other tools

† Acquisition speed depends on product class and sampling rate.‡ Vertical resolution of <60.96 cm [<2 ft] is possible.

Sonic Scanner Mechanical Specifications

Max. temperature 177 degC [350 degF]

Max. pressure 138 MPa [20,000 psi]

Borehole size

Min.

Max.

12.07 cm [4.75 in]55.88 cm [22 in]

Outer diameter 9.21 cm [3.625 in]

Length12.58 m [41.28 ft]

†

6.7 m [22 ft]‡

Weight 383 kg [844 lbm]†

188 kg [413 lbm]‡

Tension 157 kN [35,000 lbf]

Compression 13 kN [3,000 lbf]

† Advanced toolstring, including isolation joint‡ Basic toolstring, near monopoles only

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Sonic Scanner Br.ashx Slb Article