Rock
samples derived from drilling and coring remain the
most important source of data to the geoscientist. These
samples, and the direct observations they allow, supply
the benchmarks against which all other analysis can
be standardized. For this purpose and as a source of
material for geological and geochemical analysis, analyzing
cutting samples is at least as important a job function
for mud loggers as gas analysis. |
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In
addition to rock samples, it is also possible to obtain
various types of fluids from the borehole during and
after drilling. These include samples of drilling fluids,
which may contain dissolved and dispersed fractions
of minerals, volatiles, formation waters, and their
dissolved anions and cations. Formation fluid samples
can also be taken in small volumes using borehole samples
or larger volumes from flow tests of the completed wells.
The composition of formation fluids in situ will be,
of course, in equilibrium with mineralogy but will be
modified by translation to surface temperature and pressure.
It will also be modified by contamination with drilling
fluids and borehole debris, including rock cuttings
and cavings from elsewhere in the well. |
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