Page 33 - Well Logging and Formation Evaluation

Basics 23

sources having been removed). Those parts of the sample exhibiting
fluorescence are picked out and placed in a porcelain test plate hole to be
examined for cut fluorescence.

Solvent cut

To measure the solvent cut, about 3cm of dried and crushed sample is
placed in a test tube and solvent is added to about 1cm above the sample.
The test tube is shaken for a few minutes, then left to stand. The solvent
cut is the change of coloration of the solvent. Solvents that are commonly
used are chlorothene, ether, and chloroform. Precautions are required in
handling these solvents, since they are toxic and flammable. Heavy oils
generally give a stronger cut than lighter ones. Asphalts will therefore give
a stronger cut than paraffins. Condensate gives rise to only a very light
cut. In addition to the cut, a residual oil ring may be observed around the
test tube after the solvent has evaporated.
In solvent cut fluorescence, the cut fluorescence is measured by taking
the test tube used for the solvent cut and placing it under UV light together
with a sample of the pure solvent (to check for possible contamination)
and observing whether any fluorescence is present.

Acetone test

The acetone test involves placing a sample of washed, dried, and
crushed cuttings in a test tube with acetone. After shaking, the acetone is
filtered into another test tube and an equal amount of water added. Since
acetone is dissolvable in water but hydrocarbons are not, the liquid
becomes milky in color. This test is particularly useful where light oil or
condensate is present and there is no other source of carbon in the samples.

Visible staining

Particularly if the permeability and/or viscosity is poor, oil may remain
in cuttings and be visible under the microscope in the form of a stain on
the surface of the cutting.

Odor

The characteristic smell of oil may sometimes be discerned during the
cleaning and drying process.