The recognition and evaluation of hydrocarbons present in well samples is another of the more important responsibilities of the geologist.
Contamination From Previously Penetrated Beds Cavings
Owing to differences in the hardness of rocks, the type and condition of the bit and practice of the driller, one cannot set any hard and fast rule for the size of true cuttings. Caved fragments tend to be larger than fragments of rock from the bottom.
Cement fragments in cuttings are easily mistaken for sandy, silty or chalky carbonate.
In examining unwashed or poorly washed cuttings, it is often important to be able to recognize the drilling muds used. Oil-base and oil-emulsion muds coat the cuttings with oil and care must be taken to distinguish such occurrences from formation oil. Lignosulfate muds may present problems in samples used in palynological studies.
Oil Contamination, Pipe Dope, etc.
When foreign oil contamination is suspected, cuttings should be broken and their fresh surface examined. Naturally occurring oil tend to stain the chip.