May 1999 1 BTC Micro-Cylindrically Focused Log MCFL PEx* - MCFL.
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Transcript of May 1999 1 BTC Micro-Cylindrically Focused Log MCFL PEx* - MCFL.
May 19991 BTC
Micro-Cylindrically Focused LogMicro-Cylindrically Focused Log
MCFLMCFL
PEx* - MCFL
May 19992 BTC
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
May 19993 BTC
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
May 19994 BTC
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
May 19995 BTC
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
May 19996 BTC
MCFL Left Upper Quarter
May 19997 BTC
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
May 19998 BTC
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
May 19999 BTC
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
May 199910 BTC
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.
May 199911 BTC
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
May 199912 BTC
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
May 199913 BTC
Comparison MSFL-MCFL
May 199914 BTC
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
May 199915 BTC
Microlog Example
May 199916 BTC
Thinly Bedded Example
May 199917 BTC
MCFL vs. MSFL in Rugose Zones
May 199918 BTC
MCFL Comparison with FMI
May 199919 BTC
Microlog comparison