glossary

OIP describes the total hydrocarbon content of an oil reservoir.

The phase that occurs after successful exploration and development and during which hydrocarbons are drained from an oil or gas field.

Oil sand is a mixture of clay, sand, water and hydrocarbons. Hydrocarbons of oil sands have a most diverse composition, ranging from bitumen to conventional crude oil. Oil sand reservoirs are either surface-mined or extracted from deeper layers. Oils from such sands may have an API gravity of less than 10° API. Both in-situ recovery and mining methods are used to extract the resource, with surface mining used for extracting deposits of extra heavy oil at shallow depths of less than 300 ft.

The percentage of the porosity volume which is filled with oil. It is one of the main objectives of formation evaluation.

An oil shale is a sedimentary rock containing bitumen or non-volatile oils. Oil shale is also called kerogen oil or kerogen shale. Oil shale needs to be differentiated from shale oil.

Oil-base drilling fluids that typically contain synthetic fluids, diesel oil or mineral oil without much water. Oil-base muds are used for many reasons, some being increased lubricity, enhanced shale inhibition, and greater cleaning abilities with less viscosity.

This is the ratio of the volume percent oil to the volume percent water in an oil mud (see drilling mud), where each is a percent of the total liquid in the mud.
An example: if a mud contains 70 vol.% oil and 20 vol.% water, the oil percentage is [70/(70 + 20)]100 = 78% and the water percent is [20/70 +20)] = 22%. That OWR is written as 78/22.

The company that serves as the overall manager and decision-maker of a drilling project. Generally, but not always, the operator will have the largest financial stake in the project. The operator also is the owner of the right to drill or produce a well, or the entity contractually charged with drilling of a test well and production of subsequent wells.

Outside or outer diameter. Casing and tubing are commonly described in terms of inside diameter (ID) and outside diameter.