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Micro-Cylindrically Focused LogMicro-Cylindrically Focused Log

MCFLMCFL

PEx* - MCFL

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Objectives - MCFL

• High Resolution Rxo• Rxo Insensitive to Thin Mudcakes• Rxo Corrected for Thick Mudcakes• Estimation of Mudcake Thickness or Stand-

Off

The main objectives of the Platform Express microresistivity measurement are to provide:

In order to achieve:

• Invasion correction of Deep resistivity

measurement

• Detection of permeable zones

• Evaluation of sand-shale laminations

• Quantitative Sxo (moveable oil) estimate

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High-Resolution Skid - outside

MCFL MicroCylindrically focused log

B0 Main Measure Button

B1, B2 Auxiliary Measure ButtonsTDD Detector DensityLS Long Spacing DetectorSS Short Spacng DetectorBS Back Scatter Detector

B0

B1

B2

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MCFL Operation Principles

• Equipotential surfaces in front of the pad are shaped like a cylinder to fit with borehole geometry.

• This gives more accurate measurements than its predecessor (MSFL).

• Cylindrical Focusing is achieved by a combination of:

– Vertically Passive Focusing– Azimuthally Active Focusing

• Three buttons provide three depths of investigation:

– B0, B1, B2

• Finite Element Simulations are used to take into account the geometrical constraints:

– Small, long and narrow pad– Cylindrical hole and mudcake

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MCFL Principle

M - Monitor ElectrodeN - Auxiliary Voltage Electrode

A0 and A1 - Guard Electrodes

Side View

Bucking Current

Survey Current

Front View

Top View S

A1

M

A1

M

A0

B1

B0

B2

A0

N

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MCFL Left Upper Quarter

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Passive and Active Focusing

Passive Focusing (Vertical)

• To ensure measure currents from B0, B1 and B2 are focussed straight when it leaves the pad.

• Accomplished by using A0 electrode which surrounds all the measure buttons. This creates an equipotential around them.

Active Focusing (Horizontal)• To ensure equipotentials are azimuthal in

nature as it leaves the pad• To probe currents fully into invaded zone.

• Current injection from A1 is controlled by the monitoring condition:

VM - VA0 = 0

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Main MCFL Characteristics

• High vertical resolution (better than 1”) (RawB0 only)

• Shallow Rxo (3” depth of investigation)

• Rxo insensitive to mudcake up to .4” thick

• Rxo corrected for thick mudcakes (<.4”)

• Quantitative standoff estimate

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Modelling vs. Experiment

• Experimental data given by points• Modelled data given by lines

10

10 6Mudcake thickness (in.)

B*

(Ohm

.m)

Rxo = 7.7 Ohm.m, Rmc = .9 Ohm.m

B0

B1

B2

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Algorithm

Estimation performed by an ExtendedKalman Filter - objective is to minimise cost function from actual and computed measurements

Advantages:

• Noise and uncertainties taken into account

• Confidence outputs

• Real time

Former methods (charts) are no longer used.

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Operating Range of Model

• The forward model inversion works well under the following conditions:

• Outside these ranges, we are extrapolating the model, so the results cannot be guaranteed.

• Results can still be valid provided that you verify:

- Rxo’s consistent with other Rxo’s in the log

- hmc should be comparable with the TLD estimate

- Rmc should be similar to the Rmc value you measured at surface (mud sample)

Parameter Minimum Maximum

Rxo 0.02m 2m

Rxo/Rmc 3 10000

Rxo/Rm^2 10,000

hmc 0 inches 0.8 inches

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High contrast correction

• Measurement is affected in Low Rm,High Rxo

• Practical limit: Rxo/Rm^2 < 80,000 S/m– approx. 30% error– example: Rm=0.05: Rxo<200

• MAXIS High contrast correction:– (over)compensates B0 and B1– compensation can be adjusted through

2 parameters– measurements at lower Rxo not affected

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Comparison MSFL-MCFL

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Microresistivity Comparison

MSFL MCFL

Architecture Pad mounted on Integrated with densityseparate tool on HRMS skid

Focusing Spherical Cylindrical

Pad application Wide, flexible pad Narrow solid skidsubject to damage

Vertical resolution 3 in. 2 in.

Mudcake corrections Poorly defined Well defined up to 0.6 in.

Rxo limit 1000 Ohm-m 1000 Ohm-m

Auxiliary measurment synthetic Microlog Standoff, Microlog output

Length 20 ft 14 ft

Weight 335 Ibm 249 Ibm

Diameter 5 1/4 in. 4 5/8 in.

Temperature 350° F 260° F

Pressure 20,000 psi 10,000 psi

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Microlog Example

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Thinly Bedded Example

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MCFL vs. MSFL in Rugose Zones

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MCFL Comparison with FMI

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Microlog comparison