Well Logging/Nuclear
Kevin Kapka
Basic History
• The use of radiation to analyze formations appeared
shortly after World War II. The initial application was
to determine formation porosity, but it has expanded
to well Characterization, Density, and Neutron
Activation Analysis.
• It was done in secret, due to the engineers being
afraid of how the public might respond to “weapons
technology on the oil field”.
Why?
• In short $*1010
• When drilling for oil, you want to know how much oil
is in a hole you have already drilled.
The science of doing this is called Well logging.
Why Cont?
• Between the cost of the initial drilling, and then
continued production/fracking can be anywhere from
12 to 125 million.
• They don’t want to pay this price unless they have
too.
• Before well logging was a step between drilling and
production, but in modern times, we have actually
gotten to where we build well logging tools into pipe
casing.
Fundamental principles-porosity
• Conservation of Momentum. Neutrons reflect most
heavily off things with an atomic mass of 1. This
means that dense hydrocarbons are the most
reflective.
• Unfortunately, a neutron reflects equally of gas,
water, or in some freak cases, fossilized bones. All
neutron well logging gets you is neutron density.
Fundamental principles-Density
• Compton Scattering
Neutron Sources
• There are two primary sources of neutrons.
Chemical, and Accelerator based.
• Since our detectors detest most efficiently at the
Thermal and Epithermal, we need for them to scatter
down.
Slowing Down by Scattering
• We can calibrate our detectors to only detect the
thermal neutrons reflected back. We can then
characterize that reaction.
Slowing Down by Scattering
• This is a rough diagram
of the devices I have
worked on. The ratio
of near detector vs the
far detector tells you the
slowing down length.
This tells you “hydrogen”
density.
Detectors
• These detectors are usually filled with Helium 3, at
extremely high pressures. When neutrons interact
with Helium 3, via the process stated below, in a
charged tube, their interaction is “counted”.
Density
• To determine if it’s actually a hydrocarbon we then
have to get the density, and resistivity of the
formation.
• The resistivity is measured via induction.
Where Z is the atomic number, and M is the
molecular weight of the compound. They use 2
detectors, and then correct for the borehole fluid.
• This, combined with resistivity, tells us what is in the
oil.
Results
• These (density, resistivity, and
porosity) are plotted in real
time as a function of depth,
and overlaid on top of each
other.
• The dotted line is “porosity” or
hydrogen density, and the
solid line is gamma density.
• There are other ways to
measure density, and porosity
using radiation.
My job
• I am the Senior Physicist for the new Neutron
Spallation Tools.
• This uses neutron spalling as it’s neutron generator.
• It was not previously available technology due to
power consumption issues.
• Also consulted on the development of new quality
assurance mechanisms, automated well logging
analysis, firmware improvements, and training input.
My first project
• In new tools, and new
methods we have to
evaluate how “deep” into the
reservoir our tools go.
• We will pump paraffin wax
into and out of these
sheaths (while the others
are filled with
sandstone/limestone). Until
we no longer see a
response.
Neutron Spectroscopy
• If you want to see the equations, I will gladly derive
them.
• Using a high intensity neutron source, and a
thermalizing compound (usually graphite combined
with the effect of the drilling mud), we “activate” the
formation. Activation is when you get a stable isotope
to absorb a neutron.
• It then becomes unstable and begins emitting
radiation, usually in gammas. This give us
information on oil baring shales.
Graphs
This explains what is going on. We measure the radiation that comes
off of the formation, and use it to