introduction to resistivity logging. outline definitions and uses resistivity in rocks archie’s...
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Introduction toResistivity Logging
Introduction toResistivity Logging
OutlineOutline• Definitions and Uses
• Resistivity in Rocks
• Archie’s Equations
• Invasion and Invasion Models
• Measuring Resistivity (Rt and Rxo)• Basic ES Principles• Focused Devices• Micro Resistivity Devices
Resistivity UsesResistivity Uses
• Locate Hydrocarbons
• Identify Water Type
• Correlation
• Identify Lithology of Formations
ResistivityResistivity
• The opposition to flow of electrical current offered by a material of unit length and unit cross sectional area.
V
A
L
r
Measuring ResistivityMeasuring Resistivity
V - Voltage in Volts R - Resistance in Ohms
I - Current in Amperes A - Area in Square Meters
L - Length in Meters
R
V
A
L
R = r L/ A
rV/ I x A/ L
r
k = A/ L
V = R x I
V = rL/ A x I
rV/ I x k
V = I R
V = r L / A I
r = V / I k
R = r L / A
r = V/ I A / L
( k = A / L )
Archie PorosityArchie Porosity
Matrix
Oil
Water
SW = 60%
Eff. = 30%
eff
Water Wet Porosity - RoWater Wet Porosity - Ro
SW = 100%EFF = 30%
Oil And WaterOil And Water
SW = 60%EFF = 30%
Water ResistivityWater Resistivity
RW
Cube filled withSalt Water (Resistivity Rw)
Rt = RwPorosity () = 100%
Rock Matrix ResistivityRock Matrix Resistivity
Rock Cube, Rt = Porosity () = 0%
Hydrocarbon ResistivityHydrocarbon Resistivity
Oil Cube, Rt = Porosity () = 100%
Fresh-Water Filled PorosityFresh-Water Filled Porosity
Archie Cube, Rt =Porosity () = 30%
Salt-Water Filled PorositySalt-Water Filled Porosity
Resistvity 1/
Resistvity RwArchie Cube, Rt > Rw
Porosity () = 30%Rt = Ro
Salt Water & OilSalt Water & Oil
Resistvity 1/SWArchie Cube, Rt >> Rw
Porosity () = 30%
ResistivityResistivity
Which of these “Archie Blocks” has the largest resistivity
Rt = RoRt = Ro Rt > Ro
= 20%Sw = 100%
= 30%Sw = 66%
= 10%Sw = 100%
ResistivityResistivity
Which of these “Archie Blocks” has the largest resistivity
Rt = RoRt = Ro Rt > Ro
= 20%Sw = 100%
= 30%Sw = 66%
= 10%Sw = 100%
> =
True ResistivityTrue Resistivity
Rt =Rwn
Swm
a
ma
- Relates Porosity to Resistivity
m is related to the degree and type of cementation
nSw
- n usually equal to 2
Resistivity FactorsResistivity Factors
• The Formation Resistivity is effected by:
• Volume of Water - (Porosity & Sw)
• Resistivity of Water - (Rw)
• Current path through Water - “m” in Porosity equation
ResistivityResistivity
Which of these “Archie Blocks” has the largest resistivity
Rt = RoRt = Ro Rt > Ro
= 20%Sw = 100%BVW = .02
= 30%Sw = 66%
BVW = .0199
= 10%Sw = 100%BVW = .01
> =
Archie PorosityArchie Porosity
Matrix
Oil
Water
SW = 60%EFF = 30%
EFF
BVW = Sw x = 18%
Idealized Log SetIdealized Log Set
A
B
C
D
E
InvasionInvasion
Mud Filtrate Invasion
Porosity = 30 %
Porosity = 10 %
Porosity = 20 %
mud filtrate
mud filtrate
mud filtrate
mud cake
Zones About the Well-BoreZones About the Well-Bore
Rs
RtRw
Sw
Rxo
Rmf
Sxo
Di
Adjacent Bed
h VirginZone
InvadedZone
tmc - mud cake thickness
Rmc
Adjacent Bed Rm
ShaleShale
No permeability,No Invasion
Res
istiv
ity
Depth of Investigation
Virgin
10 60 90
Low InvasionLow Invasion
Water Zone
Res
istiv
ity
Depth of Investigation
Virgin
10 60 90
Low Invasion - OilLow Invasion - Oil
Low Invasion (Step) - Oil
Res
istiv
ity
Depth of Investigation
10 60 90
Virgin
Transition Zone - OilTransition Zone - OilR
esis
tivity
Depth of Investigation
10 60 90
VirginFlushed
Transition Zone - WaterTransition Zone - WaterR
esis
tivity
Depth of Investigation
10 60 90
VirginFlushed
Transition Zone - OilTransition Zone - Oil
Annulus Profile,Deep Invasion,
Oil
Res
istiv
ity
Depth of Investigation
10 60 90
VirginAnn.Flushed
Basic Log ExampleGR0 150
11000
11100
SFL.2 20
ILM.2 20DPHI 0.50
NPHI.50 0
A
B
C
D
.30
BHT = 230 FTD = 14000 ft.Rmf = 1.41 ohm-m @ 75 F
ILD.2 20S P
A
M
Electrical Survey Measurements
Unfocused SystemUnfocused System
VRa = Ik
EquipotentialSpheres
NormalDevice Lateral
Device
BN
B
Non-focused vs Focused Systems
Dual Laterolog
LLS
Ao Measure Current Electrode
M1 & M2 Monitoring Electrodes
A1 Bucking Current Emitting Electrode
A2 Bucking Current Return Electrode
LLD
Ao Measure Current Electrode
M1 & M2 Monitoring Electrodes
A1 Bucking Current Electrode
A2 Bucking Current Electrode
Spherical Focused Log
Rsfl = k (Vb - Vc)Io
Io Return to Armor
Bucking CurrentMonitoring ElectrodesBuckimg CurrentReturn ElectrodeMonitoring Electrode
Current Electrode
Proximity Log - MicrologAo Mo A1
M2
M1
Ao
AoMoA1M1M2
M2
M1
Ao
MicrologMicrolog