1. Geological Space Probes – Remote Sensing in Oil Wells (“Well Logging”)
Roger Samworth

2. Hydrocarbons:Nature Of Reservoirs (1)
Hydrocarbon reservoirs are regions of porous rock where the pore spaces are filled with oil and/or gas

3. Hydrocarbons:Nature Of Reservoirs (2)
They usually occur at depths in the ground where the pressures are many thousands of p.s.i. And temperatures normally exceed 100 deg. C

4. Hydrocarbons:Nature Of Reservoirs (3)
The pore spaces naturally contain water.
Hydrocarbons develop from the decay of organic matter, migrating upwards through the pore spaces until they encounter a geological “trap”, where they concentrate, displacing the natural water.

5. Hydrocarbons: Exploration And Production
1. Identify geological structures
2. Drill a borehole or “well”
3. Lower remote sensing probes into the hole & “log the well”
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges
6. Produce the hydrocarbon

6. Hydrocarbons: Exploration And Production
1. Identify geological structures
2. Drill a borehole or “well”
3. Lower remote sensing probes into the hole & “log the well”
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges
6. Produce the hydrocarbon

7. Hydrocarbons: Exploration And Production (1)
1. Identify geological structures e.g. Large scale seismic/gravity/magnetic surveys

8. A Seismic Survey

9. Hydrocarbons: Exploration And Production
1. Identify geological structures
2. Drill a borehole or “well”
3. Lower remote sensing probes into the hole & “log the well”
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges
6. Produce the hydrocarbon

10. Drilling A Well
Wet
Or Dry!

11. Hydrocarbons: Exploration And Production
1. Identify geological structures
2. Drill a borehole or “well”
3. Lower remote sensing probes into the hole & “log the well”
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges
6. Produce the hydrocarbon

12. Well Logging
A sensor / electronic instrument package is drawn along a borehole, recording and transmitting data along an armoured cable to a surface computer as it progresses.

13. Well Logging - Parallels With Space Probes
Remote location - difficult to fix if it goes wrong
Hostile environment -
Temperatures -40deg.C ambient to 175+deg.C
Downhole pressures up to p.s.i.
Corrosive fluids
Advanced materials required
Well logging probably biggest user of titanium outside aerospace
Extensive use of advanced polymers such as PEEK
Digital communications over long distances
Finite chance of not seeing (or hearing) the probe again !

14. The First Log Schlumberger Pechelbronn, France September 5th 1927

15. The First Logging Unit !

16. “Standard” Logging Equipment

17. “Compact” Logging Equipment

18. Open-hole Logs
Usual to run Triple combination of Nuclear , Induction and sonic tools
NMR attractive because it can estimate permeability in addition to porosity.

19. Hydrocarbons: Exploration And Production
1. Identify geological structures
2. Drill a borehole or “well”
3. Lower remote sensing probes into the hole & “log the well”
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges
6. Produce the hydrocarbon

20. Hydrocarbons: Exploration And Production
4. Cement steel pipe into hole
5. Perforate pipe with shaped explosive charges, followed possibly by pressurising the formation to fracture it (“fracing”) and make it permeable
6. Produce the hydrocarbon

21. Hydrocarbons: Exploration And Production
Typical field
Superimposed on Central London

22. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivity
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

23. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivity
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

24. Rock Type Identification
Sandstone, limestone and dolomite are common porous reservoir rocks, shale is non-porous compacted clay
Shale has a relatively high level of natural radioactivity due to clay containing traces of potassium, uranium and thorium
Sandstone is silica, limestone is calcium carbonate
Calcium and silicon can be differentiated by their different abilities to absorb low-energy gamma rays (they have different “photoelectric absorbtion cross-sections” or “PE”s)

25. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivity
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

26. Density Measurement
Dense materials absorb gamma rays more than lighter ones.
A radioactive source of gamma rays (usually Cs-137) is used to irradiate the rock formation and detectors measure the resultant scattered radiation
The intensity of this radiation is related to the formation density

27. Basic Density Tool
The presence of the borehole itself affects the measurement
Variations in the hole diameter and hole fluid density have to be accounted for
Additionally, the drilling process also disturbs the original formation

28. Drilling Induced Formation Disturbance
The drilling fluid “invades” the rock pores near the well, displacing the natural fluids
Solids in the invading fluid leave behind a “mudcake” on the borehole wall up to 15mm thick
It is necessary to apply techniques to compensate for these effects

29. Well log “Compensation”
The mudcake and / or invasion affect logs to a greater or lesser degree
Additionally, boreholes are seldom smooth and regular
To counteract these effects, logs of a similar type but having a different “measurement penetration” are combined together to compensate for the perturbations
This technique is widely used in most well log measurements

30. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivty
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

31. Neutron Porosity Measurement
Water and oil contain Hydrogen in about the same proportions.
Water = H2O, Oil = (H2C)Xn
The nucleus of a hydrogen atom is a single proton
Neutrons and protons are elementary particles making up an atomic nucleus. Neutrons have a similar mass to protons, and because they are un-charged, can approach, and interact with, positively charged atomic nuclei
A neutron has a much better chance of interacting with a particle of a similar mass to itself than with a heavier one
e.g 2 billiard balls, when colliding, interact, but a billiard ball does not interact much with a ping-pong ball
A radioactive source of fast neutrons is used to irradiate the rock formation and detectors measure the resultant neutron flux
The neutrons dominantly interact with the single proton of a hydrogen nucleus.
The resultant neutron population therefore reflects the amount of hydrogen present which, in turn, is a measure of the rock porosity

32. Neutron Porosity Tool Isotopic neutron source
2 He-3 proportional counters
“Compensation” achieved by computing ratio of count rates at the 2 detectors
N/F counts
Porosity
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

33. Interpretation And Calibration
It is important to remember that:
Density tools do not measure density
They measure gamma radiation intensity at point(s) in space
Neutron tools do not measure porosity
They measure neutron fluxes at point(s) in space.
Getting Density and Porosity is then a question of interpreting the measurement, assuming that it has been properly calibrated

34. Neutron Hydrogen Density Log
What type of probe?
Significant features
5 passes displayed
Helium -3 detectors
Source-detector spacing = 64 miles
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

35. Neutron Hydrogen Density Log
Polar aaaaa ice
What’s this aaaa then ?
How much money do you think an oil company would invest based on these logs?
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

36. Response Calibration And Characterisation Using CALLISTO
CALibration at
Leicester &
In - Situ
Tool Optimisation
EUROPA’s sister
CALLISTO is a World-standard facility for the calibration and characterisation of (predominantly) nuclear well logging probes

37. CALLISTO Calibration Facility

38. CALLISTO Calibration Facility

39. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivty
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

40. Electrical Conduction In Rock
Conduction only takes place in the fluid between the rock matrix
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

41. Induction Tool
Direct induction cancelled by “bucking” coils and by phase detection
Ground current induces current in receiver coil shifted by further 90 deg., it’s magnitude being proportional to the ground conductivity
Currents induced in ground 90 deg. phase shifted
Transmitter coil excited at 20khz
Borehole fluid need not be conductive
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

42. “Laterolog” Current Emitting Tools
Current is focussed by arrays of electrodes into different patterns
Conductive borehole fluid required
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

43. Logging The Well
a) Identify Rock Type
e.g. Measure level and nature of natural radioactivity
b) Measure Rock Porosity
e.g. Measure bulk density using gamma ray transport
(Porous rocks are less dense)
Measure hydrogen density using neutron transport
(Both water & oil contain hydrogen)
c) Identify Pore Fluids
e.g. measure electrical resistivty
low resistivity = water
high resistivity = hydrocarbon
d) Measure Rock Mechanical Properties
e.g. measure acoustic velocities

44. Acoustic Velocity Measurement
Time measured for an acoustic pulse to travel a fixed distance
“Up” and “down” measurements averaged to compensate for probe tilt
TRANSMITTERS
RECEIVERS

45. Acoustic Velocity Measurement
Waveform can be displayed as a “variable density” plot
Rock strength moduli calculated from compressional and shear-wave velocities

46. Electrical Imaging Tool (1)
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

47. Electrical Imaging Tool (2)
Original image “In-filled” image
Images are of “opened - out” borehole
Clearly shows rock features. (Strata dipping with respect to the well appear as “sine- waves”)
The spatial distribution of epithermal or thermal neutrons resulting from the interaction of fast neutrons within a formation is related to the hydrogen content. If the hydrogen is only contained within the pore space then the measurement yields porosity.
At the source energy the primary interaction is elastic scattering- in lime the mfp is ~8cm and independent of water content. But at lower energies e.g. 100 keV it ranges from 4cm in pure limestone to 2cm in 40% water-filled lime.
N transport depends on Ls and Diffusion at thermal energies until they are captured.It can be shown that the epithermal flux has an exponential dependence on Ls and diffusion coefficient
  exp(-r / Ls)
Depi.r
For thermal neutrons
  Ld^ exp(-r / Ls) - exp(-r / Ld)
D(Ls^2 - Ld^2) r
D=Ld^2.
 expressed in capture units which is 1000 times sigma in cm^-1

48. Application to Space Exploration
Seismology (“Echo sounding”)
Seismology can potentially reveal internal structure and dynamic processes of other rocky bodies—planets, moons, and asteroids— in the solar system, if seismic sensors can be deployed
Magnetometry
Magnetometers are used occasionally in well-logging, but are used extensively in space probes to investigate all sorts of magnetic properties and phenomena.
Gravimetry
Again, used occasionally in well logging to indicate density or mass anomalies, but used extensively in space probes

49. Application to Space Exploration
Neutron methods
Remember “The resultant neutron population therefore reflects the amount of hydrogen present which, in turn, is a measure of the rock porosity”
This can also indicate the presence of water, as we already discussed with respect to the Lunar orbiter albeit with a 64-mile source detector spacing! The neutron source in this case was the lunar surface itself, where neutrons were released by cosmic ray bombardment.
Neutron spectrometry
Neutron bombardment can also provoke the release of specific gamma-rays from which elemental composition can be determined

50. Application to Space Exploration
Density measurements
The Bepicolombo Mercury mission, launching this year, originally had a lander containing a mole with a density measurement. Cancelled due to cost.
Natural Radiation
Curiosity Martian rover contained a RAD detector to assess various sorts of natural radiation.

51. Conclusion 45-year career in Well-logging R&D (1972-2017)
A large variety of techniques employed
Seen dramatic changes
From the perspective of 1972:
By 2000 there would have been no oil left.
We would now be running on a coal economy
No-one worried about global warming, in fact cooling was the concern if the Gulf Stream “turned off”.
The only computing power we had in 1972 was a 4-function calculator and that belonged to Accounts!