isolation scanner

7/24/2019 Isolation Scanner

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Isolation ScannerAdvanced evaluation of wellbore integrity


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Cement placement is a critical component of a wells architecturefor ensuring mechanical support of the casing, providing protectio

from fluid corrosion, and, most importantly, isolating permeable zones

with different pressure regimes to prevent hydraulic communication.

Conventional cement bond log (CBL) and ultrasonic pulse-echo tech-

niques are sometimes used together to diagnose zonal isolation but

encounter difficulties when attempting to evaluate cements with low

acoustic impedance or cements contaminated with mud. Ambiguity can

result because these tools rely on a significant contrast in acoustic

impedance between the cement and displaced fluid to identify solids.

Isolation Scanner cement evaluation service provides more certainty bycombining the pulse-echo technique with a new ultrasonic technique th

induces a flexural wave in the casing with a transmitter and measures the

resulting signals at two receivers. The attenuation calculated between th

two receivers provides an independent response that is paired with the

pulse-echo measurement and compared with a laboratory-measured

database to produce an image of the material immediately behind the

casing. By measuring radially beyond traditional cement evaluation boundarie

Isolation Scanner service confirms zonal isolation, pinpoints any channels in

the cement, and ensures confident squeeze or no-squeeze decisions.

The signals following the casing arrivals arising from the interface

between the annulus and the borehole or outer casing can be detected

and measured. These third-interface echoes (TIEs) provide the position

f the casing within the borehole, and if the borehole size is known, the

velocity of the annulus material can be determined. This additional

information, available only through the flexural measurements, can

provide useful information for remedial applications and serve to confirm

or determine the correct interpretation for complex evaluations.

Isolation Scanner* cement evaluation service integrates the conventionapulse-echo technique with flexural wave propagation to fully characterize

the cased hole annular environment while evaluating casing condition

APPLICATIONS Differentiate high-

performance lightweight

cements from liquids

Map annulus material as

solid, liquid, or gas

Assess hydraulic isolation

Identify channels and defects

in annular isolating material

Determine casing internal

diameter and thickness

Assess annulus beyond the

casing/cement interface

Difficult to diagnose with

acoustic impedance or

CBL measurements alone

Increasingcontamination6

4

2

0

Neat

Light

8

Acoustic impedance,

Mrayl

GasLiquid

CementContaminated cement

Identifying and distinguishing various well fluids from cement with low acousticimpedance is difficult for CBL and ultrasonic pulse-echo techniques.

Isolation Scanner cement evaluationservice fully characterizes the casedhole environment, including casingposition in the borehole, borehole andouter string imaging, and materialidentification from velocity analysis.


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PITCH-CATCH PROPAGATION

The Isolation Scanner pulse-echo acoustic impedance measurement

is made with a rotating subassembly containing four transducers.

The normal-incidence transducer is oriented 180 from the other

three transducers. The three obliquely aligned transducers transmit

and receive high-frequency pulsed beams (on the order of 250 kHz)

to excite the casing in a flexural mode. Once excited in the casing,

the flexural wave propagates while radiating acoustic energy into

the annulus and back toward the receiving transducers, resulting

in a circumferential scan of the casing, annulus, cement, and near-

wellbore formation. The annulus-propagating energy is reflected at

interfaces that present an acoustic contrast, such as the cement/

formation interface, and propagates back through the casing predomi-

nantly as a flexural wave that reradiates energy into the casing fluid.

Annulus

Borehole

Formation

Casing

Time, us

80 100 110 120 130 140 150 160 170

R

T

Pulseecho

Flexural wave imaging

Pulse-echo tool

90

The Isolation Scanner sub implements thepulse-echo (normal-incidence) techniquewith four transducers: a transreceiver andthe flexural wave imager comprising onetransmitter and two receivers obliquelyaligned to excite the casing flexural mode.

Geometrical interpretation of signal propagation for the pulse-echo(blue paths) and flexural wave imaging (green paths) techniques showsthat the pitch-catch flexural wave signal separates into an early-arriving(or casing) signal and a later-arriving (TIE) signal in reference to the firstinterface encountered in the annulus (the inner and outer walls of the casingare the first and second interfaces, respectively). The attenuation of thecasing arrival amplitude complements the pulse-echo measurement todetermine whether the material behind the casing is a fluid or a solid. IfTIEs are present in the acquired data, they are used to further enhancethe characterization of the cased hole environment in terms of the state andacoustic properties (wave speed) of the material filling the annulus, the posi-tion of the casing within the hole, and the geometrical shape of the hole.

Flexural wave (TIE)

Flexural wave (casing arrival)

Ultrasonic wave


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INSIGHT THROUGH ATTENUATION

The rate of energy radiation into the annulus depends on the acoustic

properties of the annular fill. The attenuation is estimated by captur-

ing the reflected signals at two of the receivers, which are a known

distance apart, and calculating the decay rate of the received signal.

Attenuation is expressed in decibels per centimeter.

For a fluid filling the annulus, the attenuation is approximately propor-

tional to the acoustic impedance. For cement bonded to the casing, the

attenuation exhibits a more complex behavior as a function of the

velocities at which the compressional and shear waves propagate in

the cement. As shown in the plot of flexural attenuation versus acoustic

impedance for a well-bonded cement, below a critical impedance (Zc)

of approximately 3.9 Mrayl, the attenuation increases linearly with the

impedance of the annular fill, whether the fill is liquid or solid. Beyond

3.9-Mrayl Zc, only the shear waves can propagate in the cement, and

the attenuation drops sharply to small values. A high-impedance cement,

such as Class G, has an attenuation similar to that of a liquid. This

ambiguity in identifying cement is resolved by determining the acoustic

impedance of the cement with the pulse-echo technique. However, the

distinct attenuation of low-impedance cements, such as lightweight or

contaminated cements, is used to differentiate them from fluids.

Zc

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Acoustic impedance, Mrayl

SolidLiquid

Water

Gas

Flexural attenuation,

dB/cm

0 1 2 3 4 5 6

Flexural wave attenuation of a well-bonded cement is plotted as a functionof acoustic impedance for various materials. The value of Z

ccorresponds to

the critical compressional wave speed of the cement.

Three clouds of points are generated in SLG mapping of the measurementplane for a Class G cement. Zusit is the impedance determined by the pulse-echo technique; the attenuation is for the flexural wave technique.

86420-2 1

Zusit, Mrayl

1.6

1.4

1.8

1

0.8

0.6

0.4

0.2

0

0.2

GasLiquidSolid

Nominal uncontaminatedClass G cement

1.2

Attenuation,dB/cm

SOLID-LIQUID-GAS MAPPING

The first goal of Isolation Scanner processing is to provide a robust

interpreted image of the material immediately behind the casing. The

inputs are cement impedance determined by the pulse-echo mea-

surement and flexural wave attenuation computed from the amplitude of

the casing arrivals on the near and far receivers. These two independent

measurements are linked to the properties of both the fluid insidethe casing and the outside medium through an invertible relation.

Combining them accounts for the effect of the inside fluid, which

eliminates the need for logging specific fluid-property measurements

The processing output is a solid-liquid-gas (SLG) map displaying the

most likely material behind the casing. The map is computed during

an initialization step before logging by using a priori knowledge of the

possible materials:

Gas is defined as a very low impedance material, independent of

any input.

Liquid is defined as a liquid with the expected acoustic impedance

of the mud displaced by the cement, with provisions for possible

deviations from this value.

Solid is defined through the expected type of cement. A laboratory-

measured database is used to convert the material selection into

acoustic properties, again with provisions made for some contami-

nation or incompletely set cement.

Areas corresponding to inconsistencies between the measure-

ments (for example, at collars) are shown in white.

The mapped states are obtained for each azimuth by locating the

pulse-echo and flexural attenuation measurements, corrected for theeffect of the inside fluid, on the map with the areas encompassed by

each state.


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CasingCollar

Locator

10 30

Amplitudeof Echo

Minus Max.(Rugosity)

InternalRadii Minus

Average,in

MaximumInternalRadius

ExternalRadius

Average

(ERAV)

MinimumInternalRadius

4.5 3.0in

4.5 3.0in

4.5 3.0in

MinimumInternalRadius

ExternalRadius

Average

(ERAV)

MaximumInternalRadius

3.0 4.5in

3.0 4.5in

3.0 4.5in

ThicknessMinus

Average,in

Impedance,Mrayl

FlexuralAttenuation,

dB/m SLG Map

HydraulicCommun-

icationMap

500.0000

6.0000

5.6000

5.2000

4.8000

4.4000

3.6000

3.2000

2.6000

2.4000

2.0000

1.6000

1.2000

0.6000

0.40000.5000

500.0000

0.0780

0.0680

0.0520

0.0440

0.0380

0.0280

0.0200

0.0120

0.0040

0.0120

0.0280

0.0360

0.0440

0.0520

0.0600

0.0880

0.0760

500.0000

0.0780

0.0680

0.0520

0.0440

0.0380

0.0280

0.0200

0.0120

0.0040

0.0040

0.0120

0.0200

0.0280

0.03600.0440

0.0520

0.0600

0.0680

0.0760

500.0000

0.03000

2.8000

2.9091

3.0182

3.1273

3.2364

3.3454

3.5638

3.6727

3.7818

3.8909

4.0000

0.0000

50.0000

57.0000

64.0000

71.0000

78.0000

85.0000

92.0000

99.0000

106.0000

113.0000

120.0000

127.0000

134.0000

141.0000155.0000

SolidLiquidGas

SealNo seal

Depth, m

x200

x250

x300

x350

In additional to pulse-echo information on the rugosity, radius, cross section, and thickness of the 7-in [17.8-cm] casing, Isolation Scanner service processed theacoustic impedance and flexural attenuation data to produce an SLG map. Although the cement is heavy Class G, the flexural attenuation map clearly displayslow-density material from X,320 to X,270 m, revealing that the cement is contaminated in that interval. Regardless of the density difference, the material is correctlyindicated as solid on the SLG map.

By measuring radially and beyond traditional cement evaluation boundaries,

Isolation Scanner service confirms zonal isolation, pinpoints any channels

in the cement, and ensures confident squeeze or no-squeeze decisions.


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NEW MEASUREMENTS FROM FORMATION-WALL ECHOES

In addition to the SLG map identifying the annular fill immediately

behind the casing, a further Isolation Scanner objective is to extract

relevant information from the annulus/formation reflection echo or

echoes for quantifying the state of the annulus between the casing

and formation. First, the echoes following the casing arrival are detected

and their time of arrival and amplitude measured. From the time differ-ences between the reflection echoes and the casing arrivalprovided

sufficient echo azimuthal presence is available in the datathe casing

centering within the borehole can be determined. This is conveniently

presented as a percentage, with 100% representing perfect centering

and 0% for fully eccentered casing, in contact with the formation wall.

If the borehole diameter is known, the time-difference processing can

be further converted into material wave velocity and is displayed as

an annulus velocity map.

Other new measurements possible with the Isolation Scanner TIE

reflected from the cement/formation interface are

estimated wave velocity, which can be used to confirm the

SLG map and better understand cement placement

imaged borehole shape

imaged outer string to reveal corrosion and damage.

Isolation Scanner imaging of the formation wall through casing and cement revealshole enlargement (caving) in the reflection echo from the cement/formation interface attwo opposite azimuths in the intervals X,673X,675 m and X,679X,682 m. The left-sideimage, displaying the raw data at all azimuths, shows that the formation-wall echo ispresent at nearly all azimuths. Echo moveout appears sinusoidal because of casingeccentering. Each cycle represents a tool azimuthal scan.

Holeenlargement

Hole

enlargement

Casingarrival

Echo fromformation

wall

X,673

X,684

X,674

X,675

X,676

X,677

X,678

X,679

X,680

X,681

X,682

X,683

Depth, m


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Isolation Scanner Tool

Output Solid-liquid-gas map of annulus material, hydrauliccommunication map, acoustic impedance, flexuralattenuation, rugosity image, casing thickness image,internal radius image

Max. logging speed Standard resolution (6 in, 10 sampling): 823 m/h

[2,700 ft/h]High resolution (0.6 in, 5 sampling): 172 m/h[563 ft/h]

Range of measurement Min. casing thickness: 0.38 cm [0.15 in]Max. casing thickness: 2.01 cm [0.79 in]

Vertical resolution High resolution: 1.52 cm [0.6 in]High speed: 15.24 cm [6 in]

Acoustic impedance Range: 0 to 10 MraylResolution: 0.2 MraylAccuracy: 0 to 3.3 Mrayl = 0.5 Mrayl,>3.3 Mrayl = 15%

Flexural attenuation Range: 0 to 2 dB/cmResolution: 0.05 dB/cmAccuracy: 0.01 dB/cm

Min. quantifiable channel width 30 mm [1.2 in]Depth of investigation Casing and annulus up to 7.62 cm [3 in]

Mud type or weight limitation Conditions simulated before logging

Combinability Bottom only, combinable with most wireline toolsTelemetry: fast transfer bus (FTB) or enhanced FTB(EFTB)

Special applications H2S service Investigation of annulus width depends on the presence of third-interface echoes. Analysis and processing

beyond cement evaluation can yield additional answers through additional outputs, including the VariableDensity log (VDL) of the annulus waveform and polar movies in AVI format.

Differentiation of materials by acoustic impedance alone requires a minimum gap of 0.5 MRayl betweenthe fluid behind the casing and a solid.

For 8-mm [0.3-in] casing thickness.

Max. mud weight depends on the mud formulation, sub used, and casing size and weight, which aresimulated before logging.

Measurement Specifications

Isolation Scanner Tool

Max. temperature 177 degC [350 degF]

Pressure range 1 to 138 MPa [145 to 20,000 psi]

Casing sizemin. 412in (min. pass-through restriction: 4 in)

Casing sizemax. 958in

Outside diameter IBCS-A: 8.57 cm [3.375 in]IBCS-B: 11.36 cm [4.472 in]IBCS-C: 16.91 cm [6.657 in]

Length without sub 6.01 m [19.73 ft]

Weight without sub 151 kg [333 lbm]

Sub length, weight IBCS-A: 61.22 cm [24.10 in], 7.59 kg [16.75 lbm]IBCS-B: 60.32 cm [23.75 in], 9.36 kg [20.64 lbm]IBCS-C: 60.32 cm [23.75 in], 10.73 kg [23.66 lbm]

Sub max. tension 10,000 N [2,250 lbf]

Sub max. compression 50,000 N [12,250 lbf] Limits for casing size depend on the sub used. Data can be acquired in casing larger than 9 58in with

low-attenuation mud (e.g., water, brine).

Mechanical Specifications

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