1. Micro-Cylindrically Focused Log MCFL
PEx* - MCFL
Micro-Cylindrically Focused Log MCFL

2. Objectives - MCFL The main objectives of the Platform Express
microresistivity measurement are to provide:
High Resolution Rxo
Rxo Insensitive to Thin Mudcakes
Rxo Corrected for Thick Mudcakes
Estimation of Mudcake Thickness or Stand-Off
In order to achieve:
Invasion correction of Deep resistivity
measurement
Detection of permeable zones
Evaluation of sand-shale laminations
Quantitative Sxo (moveable oil) estimate

3. High-Resolution Skid - outsideB2 B1 B0
MCFL MicroCylindrically focused log
B Main Measure Button
B1, B Auxiliary Measure Buttons
TDD Detector Density
LS Long Spacing Detector
SS Short Spacng Detector
BS Back Scatter Detector

4. 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

5. MCFL Principle M - Monitor Electrode N - Auxiliary Voltage ElectrodeB2 B1 A1 A1 M M B0
Survey Current
Bucking Current A0 A0
Front View
Side View
Top View S
M - Monitor Electrode
N - Auxiliary Voltage Electrode
A0 and A1 - Guard Electrodes

6. MCFL Left Upper Quarter

7. 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

8. 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

9. Modelling vs. Experiment
Experimental data given by points
Modelled data given by lines

10. Algorithm
Estimation performed by an Extended Kalman 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.

11. 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)

12. 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

13. Comparison MSFL-MCFL

14. Microresistivity Comparison
MSFL MCFL
Architecture Pad mounted on Integrated with density
separate tool on HRMS skid
Focusing Spherical Cylindrical
Pad application Wide, flexible pad Narrow solid skid
subject 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

15. Microlog Example

16. Thinly Bedded Example

17. MCFL vs. MSFL in Rugose Zones

18. MCFL Comparison with FMI

19. Microlog comparison