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offset well |
A well drilled on the next location to the original well. The distance from the first well to the offset well depends upon spacing regulations and whether the original well produces oil or gas. |
offshore drilling |
Drilling for oil in an ocean or large lake. A drilling unit for offshore operations may be a mobile floating vessel with a ship or barge hull, a semisubmersible or submersible base, a self-propelled or towed structure with jacking legs (jack-up drilling rig), or a permanent structure used as a production platform when drilling is completed. |
ohm |
A unit of electrical resistance. The resistance of a conductive material in which a potential difference of one volt produces a current of one ampere. |
oil-base mud |
An invert-emulsion mud, or an emulsion whose continuous phase is oil. In the past, the term referred to an oil mud containing less than about 5 vol.% water. This definition, at the time, distinguished mud with less than 5 vol.% water from invert-emulsion oil muds, which had more than 5 vol.% water. Today, this distinction is not practical because most commercial oil muds can be formulated with more or less than 5 vol.% water using essentially the same types of products. |
oil-cut |
Containing less than measurable amounts of oil (describes a liquid; as oil-cut mud recovered in a drill-stem test). |
oil emulsion |
Refers to a fluid mixture, usually drilling mud, in which the continuous phase (external phase) is water and the discontinuous phase (internal phase) is oil. Electrically conductive. |
oil field |
The surface area overlying an oil reservoir or reservoirs. Commonly, the term includes not only the surface area but may include the reservoir, the wells, and production equipment as well. |
oil in place |
The amount of crude oil that is estimated to exist in a reservoir and which has not been produced. |
oil patch |
A term referring broadly to the oil field and the activities of oil and gas exploration and production. |
oil shale |
The term applied to several kinds of organic and bituminous shales, most of which consist of varying mixtures of organic matter with marlstones, shale, and clay. The organic matter is chiefly in the form of a mineraloid, called kerogen. Oil shales are widely distributed throughout the world and become of economic interest because of the large amounts of oil which can be obtained from them. |
oil stain |
Visible oil seen on surfaces of grains or fragments of rock samples. |
oil-water contact |
A bounding surface in a reservoir above which predominantly oil occurs and below which predominantly water occurs. Although oil and water are immiscible, the contact between oil and water is commonly a transition zone and there is usually irreducible water adsorbed by the grains in the rock and immovable oil that cannot be produced. The oil-water contact is not always a flat horizontal surface, but instead might be tilted or irregular. |
oil wet |
Pertaining to the preference of a solid to be in contact with an oil phase rather than a water or gas phase. Oil-wet rocks preferentially imbibe oil. Generally, polar compounds or asphaltenes deposited from the crude oil onto mineral surfaces cause the oil-wet condition. Similar compounds in oil-base mud also can cause a previously water-wet rock to become partially or totally oil-wet. |
open hole |
Uncased hole, or uncased portion of the hole. |
openhole completion |
A method of preparing a well for production in which no production casing or liner is set opposite the producing formation. Reservoir fluids flow unrestricted into the open well bore. |
operator |
The person or company, either proprietor or lessee, actually operating an oil well or lease. |
outcrop |
The exposed portion of a buried layer of rock. |
overburden |
Geostatic load. The aggregate of overlying rock column including the fluids contained within the pores of the rock. |
overpressure |
Is an expression which has been used commonly to refer to high pressure found in some formations; super-normal pressure or surpressure. Technically, it should be said that overpressure is that amount of pore pressure which is in excess of normal pore pressure in overpressured formations. |
overshot |
A downhole tool used in fishing operations to engage on the outside surface of a tube or tool. A grapple, or similar slip mechanism, on the overshot grips the fish, allowing application of tensile force and jarring action. If the fish cannot be removed, a release system within the overshot allows the overshot to be disengaged and retrieved. |
