NMR (first) 'Rocked' in the '60s
NMR Measurements Potential
NMR (first) 'Rocked' in the '60s
The potential of NMR measurements
to provide information on formation pore fluids and pore structure
was first identified in the 1950s. The first NMR log was run in
1960, measuring the signal from protons precessing in Earth's magnetic
field.
These early NMR logging tools required
doping the drilling mud with magnetite to kill the borehole signal.
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NMR (first) 'Rocked' in the '60s
The potential of NMR measurements
to provide information on formation pore fluids and pore structure
was first identified in the 1950s. The first NMR log was run in
1960, measuring the signal from protons precessing in Earth's magnetic
field.
These early NMR logging tools required
doping the drilling mud with magnetite to kill the borehole signal.
Advances in NMR interpretation occurred
in the 1960s, including a relationship between relaxation time and
permeability in sandstones, the concept of free fluid index and
the relationship between pore size, fluid and matrix properties.
A new version of the tool was developed
in the late 1970s and remained the only widely available NMR tool
until the advent of the pulsed NMR tools in the late 1980s. This
new generation tool had a T2 (the amount of time it takes for the
magnetization component to deteriorate) sensitivity limit of about
30 milliseconds and measured only the bulk or movable fluid in the
formation pores.
It did not measure the T2 distribution
of the pore fluid.
The first commercial pulse-echo logging
tool was introduced in 1990, and Schlumberger introduced its first
commercial tool in 1994. Schlumberger's Combinable Magnetic Resonance,
or CMR, tool was first proposed in the late 1980s and a prototype
was field tested in 1992.
In 1994 the commercial CMR tool had
a T2 sensitivity limit of three milliseconds. It couldn't routinely
measure T2 signals below three milliseconds, such as those from
clay-bound water or water trapped in small pores.
Schlumberger improved the technology
with its CMR-200 and Total CMR (TCMR) porosity processing — enhancing
the T2 sensitivity limit by an order of magnitude to 0.3 milliseconds.
The TCMR porosity processing software was optimized to make full
use of the hardware improvements in the determination of total porosity.
TCMR logs demonstrated that in most formations the tool is capable
of measuring total porosity.
NMR data can be used directly to
infer formation properties — and comparing NMR with other measurements
can expand on this information. For example, comparisons with density
porosity can be used to quantify gas or light hydrocarbons in shaly
sand and other difficult environments.