1. General remarks on sample escription

1. The major changes in the formations should be noted and the appearance of new formation martial should be described as carefully as possible.

2. The logger upon coming on duty should familiarise himself with the samples from formations drilled while he was off-duty. This will aid him in soothing cavings and changes of formation characters.

3. In some cases the sample retrieved will not represent the formation at all. For example, evaporites sections drill with a fresh water base mud will dissolve the formation salts as they rise in the annulus. In this case the previous mentioned criteriae should be borne in mind.

4. In arriving at the geological descriptions of the formation drilled, such things as drilling rate and present depth of the bit should be taken into consideration. At fairly deep depths there is a tendency for cutting from a formation to become dispersed along the mud column and straggling out sometime after the formation has been drilled through. For instance after a sand has been drilled through, cuttings from this sand may continue to appear in samples for time.

5. Always bear in mind that contamination of an intervals cutting can occur for several reasons and must be excluded from the description.

36. Contamination of cuttings

Contamination of the cuttings is a direct result of the rig operations. Setting of casing, the mud additives, or any hole problems like pipe stuck, etc..., Can all lead to a cuttings contamination. Contamination may or may not be easily detected. This depends on the logger’s experience.

Below is a chart identifying some of the more common contaminants:-

TYPE	SOURCE	MISTAKEN FOR	CHARACTERISTICS
Mica	lost circulation material	a mineral that has been broken away from the rock	much larger flakes than found in most rocks, thick block (may layers), colourless or transparent in thin sheets, yellow or brown in thick blocks.
Lignite	thinners or dispersants	natural lignite or coal	lighter than cutting, reacts with water to give a slight coloration , brownish to black in colour, usually floats on water
Cement	Ceementing casing pipe or cement plugs	calcareous siltstone, limestone	medium gary to white with black specks calcareous reacts with phenolphthalein and turns purple
Plastic beads	torque reducer	well rounded sand	transparent well rounded well sorted medium grain, lighter than water
Seed husks	lost circulation material	-	looks just like seed husks
Walnut hulls	lost circulation material	dark brown siltstone	lighter than cuttings and heavier than water so when it is agitated with water the rock cuttings will remain in place and the walnut hulls will move with water, light to dark brown with a distinct darker coloration on the surface, unique texture (detected by chewing)
Rubber	dissplacement plugs used in cementing (drilled out)	-	red or black rubber
Metal filings	from drill bit or pipe	-	metallic when fresh but may look like red siltstone or limonite when oxidized

U.V Box Contamination

When using the UV box, one must be certain that they are actually looking at a hydrocarbon bearing rock. There have been cases of false oil shows turned in due to practical jokes. Here is a list of a few common contaminants.

Type	Colour	characteristics
Pipe dope	bright blue	will cut using chlorothene
coffee grounds	dull green	with not cut
Some oil base mud additives	variety of colours	most will cut when using chloroethane.