glossary

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Heavy oil	Crude oil with high viscosity and high specific gravity below 22.3° API-gravity. In addition to high viscosity and high specific gravity, heavy oils typically have low hydrogen-to-carbon ratios, high asphaltene, sulfur, nitrogen, and heavy-metal content, as well as higher acid numbers.

High-pressure, high-temperature (HTHP) well	Referring to wells that are hotter or show higher pressure than most other wells. In the UK, HPHT is formally defined as a well having an undisturbed bottomhole temperature of greater than 300oF (149oC) and a pore pressure of at least 0.8 psi/ft. (~15.3 lbm/gal) or requiring a Blowout Preventer with a rating in excess of 10,000 psi [68.95 MPa].

Horizontal drilling	A subset of the more general term directional drilling, used where the departure of the wellbore from vertical exceeds about 80 degrees. Note that some horizontal wells are designed such that after reaching true 90-degree horizontal, the wellbore may actually start drilling upward. Because a horizontal well typically penetrates a greater length of the reservoir, it can offer significant production improvement over a vertical well. Horizontal drilling is common in shale reservoirs because it allows drillers to place the borehole in contact with the most productive reservoir rock.

Hostile environment	A particularly difficult set of well conditions that may detrimentally affect steel, mud additives, electronics, or tools and tool components. Such conditions mostly include very high temperatures, the presence of acid gases (H2S, CO2), chlorides, high pressures and, more extreme measured depths. See also High-pressure, high-temperature (HTHP)

Hydraulic fracturing	Process of stimulating (see stimulation) oil and gas wells in low-permeability reservoirs, such as shale. Special fluids are pumped at very high pressure and rate into the reservoir to create fractures in the formation. Proppants such as grains of sand are mixed with the special fluid to keep the fracture open through which hydrocarbons can flow.

Hydrocarbon	A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Most of naturally found hydrocarbons occur in crude oil (liquid state). However hydrocarbons can occur as gases (see natural gas) or solids (coal) as well.

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