Wireline LoggingWireline Logging

Resistivity & SP ToolsResistivity & SP Tools

OverviewOverview

• Formation: Reservoir qualityFormation: Reservoir quality

• Fluid: Oil, Gas or Water? Fluid: Oil, Gas or Water?

• Borehole: Environmental factorsBorehole: Environmental factors

Formation PropertiesFormation Properties

• RadioactivityRadioactivity

• PorosityPorosity

• Grain densityGrain density

• Pore SizePore Size

• StratigraphyStratigraphy

• Bedding, DipBedding, Dip

• Sonic VelocitySonic Velocity

• Seismic VelocitySeismic Velocity

Fluid PropertiesFluid Properties

• Salinity (Resistivity)Salinity (Resistivity)

• DensityDensity

• SaturationSaturation

• PressurePressure

• TemperatureTemperature

• ViscosityViscosity

• MobilityMobility

• Bubble PointBubble Point

Borehole PropertiesBorehole Properties

• DepthDepth

• CaliperCaliper

• Spontaneous PotentialSpontaneous Potential

• TemperatureTemperature

• Cable TensionCable Tension

• Deviation, AzimuthDeviation, Azimuth

Basic ResistivityBasic Resistivity

• Resistivity (Ohms) = Voltage / Resistivity (Ohms) = Voltage / CurrentCurrent

• Archie’s Equation:Archie’s Equation:– (a/porosity(a/porositymm x Rw / Rt) x Rw / Rt)1/n1/n

Formation ResistivityFormation Resistivity

h

Rs

Rt

Rw

Sw

Rxo

Rmf

Sxo

Di

Adjacent Bed

VirginZone

InvadedZone

tmc - mud cake thickness

Rmc

Adjacent Bed Rm

Mud InvasionMud Invasion

Resistivity LoggingResistivity Logging

• Electrode type tools (resistivity)Electrode type tools (resistivity)– LaterologLaterolog– Micro Speherically Focused (MSFL)Micro Speherically Focused (MSFL)

• Induction Tools (conductivity)Induction Tools (conductivity)– Dual Induction/HRIDual Induction/HRI– Array Induction ToolsArray Induction Tools

• Conductivity = 1/ResistivityConductivity = 1/Resistivity

Electrode Type ToolsElectrode Type Tools

• Force (AC) current between two (or more) Force (AC) current between two (or more) electrodes.electrodes.

• Measure voltage between two Measure voltage between two intermediate electrodes.intermediate electrodes.

• Force current to flow in zone of interest by Force current to flow in zone of interest by using ‘bucking’ currents.using ‘bucking’ currents.

• Do not work in non conductive muds such Do not work in non conductive muds such as OBM.as OBM.

• Can give extremely high resolution and Can give extremely high resolution and depth of investigation.depth of investigation.

Laterolog PrincipleLaterolog Principle

Bucking CurrentsBucking Currents

Dual Laterolog ToolsDual Laterolog Tools

• Two depths of investigation – LLD and Two depths of investigation – LLD and LLSLLS

• Deep current returns to a surface Deep current returns to a surface electrode.electrode.

• Insulated bridle to give a far deep Insulated bridle to give a far deep voltage reference.voltage reference.

• Normally run together with MSFL to Normally run together with MSFL to give Rxo.give Rxo.

MSFL PrincipleMSFL Principle

MSFL ToolMSFL Tool

• Pad based tool, similar to density.Pad based tool, similar to density.

• Pad is kept in contact by a caliper.Pad is kept in contact by a caliper.

• Pad uses a spherical pattern of Pad uses a spherical pattern of bucking currents to focus measure bucking currents to focus measure current.current.

• Can be affected by hole rugosity.Can be affected by hole rugosity.

• Pad is rubber and can be damaged.Pad is rubber and can be damaged.

Induction PrinciplesInduction Principles

Dual Induction ToolsDual Induction Tools

• Two coil arrays emit a high frequency signal to Two coil arrays emit a high frequency signal to excite the formation.excite the formation.

• The formation current generates a weak The formation current generates a weak seconday signal which is detected by receiver seconday signal which is detected by receiver coils.coils.

• Strong direct signal from transmitter is (approx) Strong direct signal from transmitter is (approx) 90 deg out of phase with formation signal.90 deg out of phase with formation signal.

• Formation signal is focused by combination of Formation signal is focused by combination of coils in array and by source receiver spacing.coils in array and by source receiver spacing.

• Reading will be compromised by highly Reading will be compromised by highly conductive (saline) water based muds.conductive (saline) water based muds.

• Normally poorer vertical resolution and depth of Normally poorer vertical resolution and depth of investigation than laterolog tools.investigation than laterolog tools.

Array Induction toolsArray Induction tools

• Large number of simpler coils at many Large number of simpler coils at many different spacings.different spacings.

• The data from all the coils at different The data from all the coils at different frequencies and phases is used at surface frequencies and phases is used at surface to compute focused Resistivity readings.to compute focused Resistivity readings.

• Depths of investigation and vertical Depths of investigation and vertical resolution become software selectable.resolution become software selectable.

• Can be focussed as close as 10” Can be focussed as close as 10” horizontally and 12” vertically.horizontally and 12” vertically.

• More sensitive to erratic tool motion.More sensitive to erratic tool motion.

SP PhysicsSP Physics

Spontaneous PotentialSpontaneous Potential

• One of the first wireline measurements.One of the first wireline measurements.

• Can be used to identify sand, shale, VclCan be used to identify sand, shale, Vcl

• Can be used to derive RwCan be used to derive Rw

• Based on the contrast between Rmf and Rw.Based on the contrast between Rmf and Rw.

• Chlorine ions are more mobile than Sodium Chlorine ions are more mobile than Sodium (NaCl) and migrate from the lower (NaCl) and migrate from the lower resistivity zone to the higher.resistivity zone to the higher.

• This creates a polarisation.This creates a polarisation.

SP Operational LimitationsSP Operational Limitations

• Only works in conductive muds.Only works in conductive muds.

• If Rmf > Rw looks similar to GR.If Rmf > Rw looks similar to GR.

• In opposite case polarity is reversed.In opposite case polarity is reversed.

• Requires a downhole electrode Requires a downhole electrode (laterolog bridle) and surface electode.(laterolog bridle) and surface electode.

• Can be compromised by electrical noise Can be compromised by electrical noise (welding etc) or magnetised cable (welding etc) or magnetised cable drums.drums.

SP LogSP Log

Resistivity Test 1Resistivity Test 1

1.1. Which three of the following are normally Which three of the following are normally measured in the invaded zone: Rw, Sxo, Rxo, Rt, measured in the invaded zone: Rw, Sxo, Rxo, Rt, Rmf, Sw?Rmf, Sw?

2.2. In a fresh mud system where Rmf>Rw the deep In a fresh mud system where Rmf>Rw the deep resistivity would normally be (HIGHER/LOWER) resistivity would normally be (HIGHER/LOWER) than the shallow?than the shallow?

3.3. What is the definition of conductivity?What is the definition of conductivity?4.4. Name the tool types that are normally referred to Name the tool types that are normally referred to

as ‘electrode’ type tools.as ‘electrode’ type tools.5.5. On electrode type tools why do we not normally On electrode type tools why do we not normally

measure voltage at the same electrodes as the measure voltage at the same electrodes as the current flows to/from?current flows to/from?

Resistivity Test 2Resistivity Test 2

6.6. How to we focus the current to flow in the How to we focus the current to flow in the zone of interest?zone of interest?

7.7. On a laterolog tool where do the shallow and On a laterolog tool where do the shallow and deep currents flow to?deep currents flow to?

8.8. Why does a laterolog use an insulated bridle?Why does a laterolog use an insulated bridle?9.9. What other tool is normally run in What other tool is normally run in

combination?combination?10.10.Which of the following tools has a built in Which of the following tools has a built in

caliper? (Array Induction, Dual Laterolog, caliper? (Array Induction, Dual Laterolog, MSFL, Dual Induction)MSFL, Dual Induction)

Resistivity Test 3Resistivity Test 3

11.11.Name two factors that can affect the MSFL Name two factors that can affect the MSFL reading.reading.

12.12.Why does the formation signal for an induction Why does the formation signal for an induction tool not get swamped by the direct signal from tool not get swamped by the direct signal from the transmitter coil?the transmitter coil?

13.13. Induction tools work best in which mud type Induction tools work best in which mud type (Saline/Non Conductive).(Saline/Non Conductive).

14.14.Laterolog type tools work best in which mud Laterolog type tools work best in which mud type (Saline/Non Conductive).type (Saline/Non Conductive).

15.15.MSFL type tools work best in which mud type MSFL type tools work best in which mud type (Saline/Non Conductive).(Saline/Non Conductive).

Resistivity Test 4Resistivity Test 4

16.16.SP is an acronym for what borehole SP is an acronym for what borehole property?property?

17.17.The SP measures a voltage or a current?The SP measures a voltage or a current?

18.18.The SP system uses 2 electrodes – where The SP system uses 2 electrodes – where are they located.are they located.

19.19.If the SP deflects in the same direction If the SP deflects in the same direction as the GR is Rmf greater or less than Rw?as the GR is Rmf greater or less than Rw?

20.20.Name two causes of bad SP logs.Name two causes of bad SP logs.