1 FE – OverviewFarag July 2002
Resistivity Logging
2 FE – OverviewFarag July 2002
Resistivity LogResistivity Log
• Basics about the Resistivity:
• Resistivity measures the electric properties of the formation,• Resistivity is measured as, R in W per m,• Resistivity is the inverse of conductivity,• The ability to conduct electric current depends upon:
• The Volume of water, • The Temperature of the formation,• The Salinity of the formation
The Resistivity Log: Resistivity logs measure the ability of rocks toconduct electrical current and are scaled in units of ohm-meters.The Usage: Resistivity logs are electric logs which are used to:
Determine Hydrocarbon versus Water-bearing zones, Indicate Permeable zones, Determine Resisitivity Porosity.
3 FE – OverviewFarag July 2002
Resistivity
• Resistivity is the opposition to flow of electrical current offered by a material of unit length and unit cross sectional area. It is a property of the material itself, not of its shape or dimensions.
Unit length, L
Current, I
Voltage, V
Unit area, A
4 FE – OverviewFarag July 2002
Resistance and Resistivity
• Ohms Law: V = I R
• Resistance, R = r (L / A)
• Therefore V = I r (L / A)
• So r = (V / I) (A / L)
• Let k = A / L (Geometric Factor)
• So, r = (V / I) k
5 FE – OverviewFarag July 2002
Conductance and Conductivity
• Conductance is the reciprocal of resistance. It represents the ease with which current flows through a given circuit.
• Conductivity is the reciprocal of resistivity. It represents the ease with which current flows through a certain material. It is a property of the material itself.
• Resistance unit: ohm (Ω)• Resistivity unit: ohm-meter (Ω·m2/m, or Ω ·m)• Conductance unit : siemens or mho • Conductivity unit: siemens/meter or mho/meter.
6 FE – OverviewFarag July 2002
Resistivity Logging
There are two types of resistivity logging tools:
• Laterolog tools send a current from electrodes on the logging tool, through the formation, to a return electrode located either at surface or downhole.– Laterolog tools need a conductive path between the logging tool
and the formation
• Induction tools generate current loops in the formation and measure the strength of the electromagnetic signal created by these current loops. – Induction tools do not require a conductive path in the borehole.
They work in oil-base muds and air-filled holes.
7 FE – OverviewFarag July 2002
Basic Resistivity tool types
Induction Logging ToolsLaterolog Logging Tools
8 FE – OverviewFarag July 2002
RxoRt
Rm
Rm
Rxo
Rt
Logging ToolBorehole
Uninvaded Zone
Invaded Zone
Laterolog vs. Induction Current Path
Laterolog Response
Induction Response
9 FE – OverviewFarag July 2002
Resistivity
There are two main techniques for measuring resistivity:
Laterolog : Current is injected into the formation
Induction : Current loops are induced in the formation
10 FE – OverviewFarag July 2002
LatrologsPEx-HALS
11 FE – OverviewFarag July 2002
Resistivity : Laterolog
Current is forced through the mud into the formation
12 FE – OverviewFarag July 2002
Dual Laterolog Measurement
LLD: deep measurement, currect returns to surface.
LLS: shallow measurement, current returns to the tool itself.
13 FE – OverviewFarag July 2002
Bucking Current
Measure Current
A2
A1
M2
M1
A0
280 HzCurrentSource
MonitoringLoop
Resistivity : Laterolog Shallow (LLS)
14 FE – OverviewFarag July 2002
Bucking Current
Measure Current
A2
A1
M2
M1
A0
A1*
35 Hz Aux Mon.
Loop
MonitoringLoop
Bucking Current
FishLCM Module
35 Hz Current
Resistivity : Laterolog Deep (LLD)
15 FE – OverviewFarag July 2002
Resistivity : Laterolog invasion effects
RLL = Vm Rm + Vmc Rmc + Vxo Rxo + (1-Vm-Vmc-Vxo) Rt
16 FE – OverviewFarag July 2002
Resistivity : Laterolog
17 FE – OverviewFarag July 2002
Resistivity : Laterolog invasion effects
Rmc
Rm
RXO
Rt
Ra = VRm(Rm) + VRmc(Rmc) + Vrxo(Rxo) + VRt(Rt)
18 FE – OverviewFarag July 2002
If Rmf < Rw then Rxo < LLS < LLD < RtIf Rmf > Rw then Rxo > LLS > LLD > Rt
Using Rxo, LLS & LLD, Rt and Di can be computed
Resistivity : Laterolog invasion effects
19 FE – OverviewFarag July 2002
Resistivity : Laterolog invasion effects
20 FE – OverviewFarag July 2002
Resistivity : Laterolog azimuthal measurements
21 FE – OverviewFarag July 2002
LatrologsEnvironmental corrections
22 FE – OverviewFarag July 2002
Groningen Effect
• Caused by highly resistive beds overlying the formation that is being measured.
• This forces the deep current into the mud column.
• This is caused by the voltage reference (cable-torpedo) becoming non-zero.
• LLd reads too high• More pronounced at low resistivity
23 FE – OverviewFarag July 2002
Borehole & Invasion Effects
Ra = Vm*Rm + Vxo*Rxo + Vt*Rt
Resistivities measured in series
24 FE – OverviewFarag July 2002
Invasion Enhances Shoulder Effects
25 FE – OverviewFarag July 2002
Shoulder-Bed Squeeze Effects
Deep measurement reads too high and results in erroneous invasion
profile.
All resistivities read lower than Rt and separation is reduced.
26 FE – OverviewFarag July 2002
Platform Express HRL FMI
LatrologsHRLA (High Resolution Array Laterolog)
27 FE – OverviewFarag July 2002
HRLA Solutions Hardware
Mode 1 Mode 2 Mode 3
Mode 4 Mode 5
Multiple depth of investigation• Clear indication of invasion• Improved vertical resolution• No need for deep mode or bridle• No Groningen or drillpipe-
conveyed logging effects and reduced shoulder-bed effect
28 FE – OverviewFarag July 2002
29 FE – OverviewFarag July 2002
HRLA 1D Real-time Answer
Real-time wellsite product gives clear answers for quick decisions:
- Eliminates voltage reference effects
- Less shoulder-bed effect
- Self consistent depth matched measurements
30 FE – OverviewFarag July 2002
Answer Benefits: Reduced Shoulder-bed Effect
HRLA tool HALS tool 1D-Rt comparison
1D radial model
(invasion)thick-bed
approximation
31 FE – OverviewFarag July 2002
Answer Benefits: No Groningen Effect
Curve separation suggests
invasion but is due to
Groningen effect
HRLA resistivities clearly show zone is not invaded
32 FE – OverviewFarag July 2002
Answer Benefits: Thin-Bed and Invasion Profiling
Curve separationshows invasion
High verticalresolution
Curve separation results from Groningen effect
Groningen effectin indicator curve
HRLA tool DLL tool
33 FE – OverviewFarag July 2002
HALS - standard and hires
SHALE
SAND
34 FE – OverviewFarag July 2002
HALS LQC
Groningen flag
35 FE – OverviewFarag July 2002
LQC - Out of limits (example)
HIGH RESISTIVITY BED
36 FE – OverviewFarag July 2002
HALS - out of limits
HIGH RESISTIVITY BED
37 FE – OverviewFarag July 2002
HALS NoisePrimarily from Rig Generator
Rig Generator OFF Rig Generator ON
38 FE – OverviewFarag July 2002
InductionsAIT
39 FE – OverviewFarag July 2002
AIT-H Stand-Off Positioning
40 FE – OverviewFarag July 2002
Resistivity : Induction
41 FE – OverviewFarag July 2002
Resistivity : Induction
42 FE – OverviewFarag July 2002
Operating Range
• 0.1 to 2000 ohmm• Moderate Rxo < Rt• Rt/Rm <100 (with hole diameter
considered)• Large diameter holes with moderate Rt/Rm
and moderate Rt
43 FE – OverviewFarag July 2002
Induction response errors
• Skin effect & Mutual Inductance• Borehole effect• Cave effect• Shoulder effect• Invasion effects
44 FE – OverviewFarag July 2002
Rmc
Rm
RXO
Rt
Resistivity : Induction
1/Ra = 1/(VRm(Rm)) + 1/(VRmc(Rmc)) + 1/(Vrxo(Rxo)) + 1/(VRt(Rt))
45 FE – OverviewFarag July 2002
If Rmf < Rw, AT10 < 20 < 30 < 60 < 90If Rmf > Rw, AT10 > 20 > 30 > 60 > 90
From the 5 curves Rt can be computed
Resistivity : Induction
46 FE – OverviewFarag July 2002
Resistivity : InductionFocusing
47 FE – OverviewFarag July 2002
Resistivity : InductionHole size and shapeUncertainty in hole size or mud resistivity can cause large errors on the shallow curves but much smaller errors on the deeper measurements
Out of sequence
48 FE – OverviewFarag July 2002
Resistivity : InductionInvasion
Very deep invasion can affect even the deepest measurements, non-cylindrical invasion may affect the Rt computation
49 FE – OverviewFarag July 2002
Induction Resistivity in Deviated Wells
Relative dip angle
Shallow Resistivity Deep Resistivity
low relativedip angle
high relativedip angle
50 FE – OverviewFarag July 2002
Inductions vs Laterologs
51 FE – OverviewFarag July 2002
Comparison to AIT
BS = 8”
Rt = 200
Rxo = 30
Rm = 0.1
S/O = 1.5”
52 FE – OverviewFarag July 2002
BS=8.5Rm=0.5Rxo=5.0Rt=200
Resistivity : Tool planner
53 FE – OverviewFarag July 2002
BS=12Rm=0.5Rxo=5.0Rt=200
Resistivity : Tool planner
54 FE – OverviewFarag July 2002
BS=12Rm=1Rxo=5.0Rt=200
Resistivity : Tool planner
55 FE – OverviewFarag July 2002
BS=16Rm=1Rxo=5.0Rt=200
Resistivity : Tool planner
56 FE – OverviewFarag July 2002
BS=24Rm=1Rxo=5.0Rt=200
Resistivity : Tool planner
57 FE – OverviewFarag July 2002
BS=24Rm=1Rxo=5.0Rt=100
Resistivity : Tool planner
Top Related