H

Hardness (water).: The hardness of water is due principally to calcium and magnesium ions. The total hardness is measured in terms of parts per million of calcium carbonate or calcium and sometimes epm of calcium. See: API RP 13B.
Head.: The height a column of fluid would stand in an open-ended pipe if it was attached to the point of interest. The head at the bottom of a 1000-ft well is 1000ft, but the pressure would be dependent on the density of the drilling fluid in the well.
Heaving.: The partial or complete collapse of the walls of a hole resulting from internal pressures due primarily to swelling from hydration or formation pressures or from internal stresses. See: sloughing.
Heavy solids.: See: high-gravity solids.
Hertz.: A unit of frequency: cycles per second.
Heterogeneous.: A substance that consists of more than one phase and is not uniform, such as colloids, emulsions, etc. It has different properties in different parts.
High-gravity solids (HGS).: Solids purchased and added to a drilling fluid specifically and solely to increase drilling-fluid density. Barite (4.2 specific gravity) and hematite (5.05 specific gravity) are the most common additives used for this purpose. See: low-gravity solids.
High-pH drilling fluid.: A drilling fluid with a pH range above 10.5. A high-alkalinity drilling fluid. See: pH.
High-yield clay.: A classification given to a group of commercial drillingclay preparations having yield of 35 to 50 bbl/ton, an intermediate rating between bentonite and...

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Drilling Fluids Processing Handbook

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