Oil & Gas Terms in Category H

Hydraulic holddown

An accessory or integral part of a packer used to limit the packer’s upward movement under pressure.

Hi-lo cam

A mechanism in some packers to set and release the tool with a minimum of rotation


Organic compounds of hydrogen and carbon, whose densities, boiling points, and freezing points increase as their molecular weights increase.

Although composed of only two elements.

Hydrocarbons exist in a variety of compounds because of the strong affinity of the carbon atom for other atoms and for itself.

The smallest molecules of hydrocarbons are gaseous; the largest are solids.

Petroleum is a mixture of many different hydrocarbons.

Hydraulic hammer effect

A phenomenon in which a pressure concession occurs by suddenly stopping the flow of liquids in a closed container.

Also called water hammer.



An arrangement of pulleys and wire rope or chain used for lifting heavy objects; a winch or similar device.


The drawworks; to raise or lift

Hydrostatic head

See hydrostatic pressure


A worker in the oil industry, especially one in the field.

Heavy crude oil

Heavy crude oil or extra heavy crude oil is any type of crude oil which does not flow easily.

It is referred to as “heavy” because its density or specific gravity is higher than that of light crude oil.

heavy crude oil has been defined as any liquid petroleum with an api gravity less than 20°, meaning that its specific gravity is greater than 0.933.

This mostly results from crude oil getting degraded by being exposed to bacteria, water or air resulting in the loss of its lighter fractions while leaving behind its heavier fractions.

Hydraulic head

The force exerted by a column of liquid expressed by the height of the liquid above the point at which the pressure is measured.

Although “head” refers to distance or height, it is used to express pressure, since the force of the liquid column is directly proportional to its height.

Also called head or hydrostatic head.

Compare hydrostatic pressure.


An instrument with a graduated stem, used to determine the gravity of liquids.

The liquid to be measured is placed in a cylinder, and the hydrometer dropped into it.

It floats at a certain level in the liquid (high if the liquid is light, low if it is heavy), and the stem markings indicate the gravity of the liquid.


See casing hanger, tubing hanger

H2s form

Hydrogen sulfide



Health, safety and environment.

Hydraulic pump

An artificial lift system that is powered by injected fluid (usually water), that powers a pump similar to the rotating pump used in electrical submersible pumps.


The mineral form of ferric oxide [fe2o3].

The hematite ore used as a weighting material in drilling muds has a mica-like crystal structure that grinds to particle size suitable for use in drilling fluids.

To check for potential wear, an abrasion test is usually run on hematite as a quality control pilot test.

alternate form: haematite