Page 493 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:30 PM Page 469

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Glossary

material that may tend to produce detrimental properties of the
drilling fluid. In some cases, contamination can damage producing
formations.

Continuous Phase. The fluid phase which completely surrounds the
dispersed phase that may be colloids, oil, etc.

Controlled Aggregation. A condition in which the clay platelets are
maintained stacked by a polyvalent cation such as calcium and are
deflocculated by use of a thinner.

Conventional Mud. A drilling fluid containing essentially clay and water.

Coring. The act of procuring a sample of the formation being drilled
for geological information purposes. Conventional coring is done by
means of a core barrel put on the bottom of the drill pipe where the
bit normally operates. As the cutter head of the core barrel pene-
trates the formations a continuous sample of the formation is taken
in the core barrel and later withdrawn with the drill pipe. The wire
line core barrel is used in many areas since it permits coring to be
done without withdrawing the drill pipe from the well bore between
cores. Sidewall cores are formation samples taken from the wall of
the well’s borehole by a wireline deployed tool.

Correlated Electromagnetic Retrieval Tool. Schlumberger wireline
fishing tool which can retrieve ferrous junk in cased or open hole.

Corrosion. The adverse chemical alteration on a metal or the
eating away of the metal by air, moisture or chemicals; usually an
oxide is formed.

Covalent. A chemical bond between atoms whereby incomplete elec-
tron orbits in the bonded atoms are satisfied by the two atoms’ ‘shar-
ing’ one electron. Some covalent compounds do display some ionic
character, where the sharing is somewhat unequal (e.g., water) and
the compound is then said to be polar. Polar covalent compounds
(e.g., alcohol) are generally soluble in water whereas non-polar cova-
lent compounds (e.g., diesel) are not.

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