1. to start the mud pump for restoring circulation of the mud column. because the stagnant drilling fluid has thickened or gelled during the period of no circulation, high pump pressure is usually required to break circulation.
2. to establish circulation of drilling fluids after a period of static conditions. circulation may resume after a short [...]

A downhole tool typically used with motors or assemblies that restrict the allowable fluid-circulation rates. when operated, the circulation sub allows a higher circulation rate to be established by opening a path to the annulus in the top section of the tool string. this is especially useful in applications such as drilling in slim-diameter wells, where a [...]

A drilling technique whereby gases (typically compressed air or nitrogen) are used to cool the drill bit and lift cuttings out of the wellbore, instead of the more conventional use of liquids. the advantages of air drilling are that it is usually much faster than drilling with liquids and it may eliminate lost circulation problems. the disadvantages [...]

An adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore (iadc definition).

Drilling in which the size of the hole is smaller than the conventional hole diameter for a given depth. this decrease in hole size enables the operator to run smaller casing, thereby lessening the cost of completion. see miniaturized completion.

The course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus. seldom used in open hole, but frequently used in workover operations. also referred to as “circulating the short way,” since [...]

Drilling for oil or gas in an ocean, gulf, or sea, usually on the outer continental shelf. 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 (jackup drilling rig), or a permanent structure [...]

The smooth, uninterrupted circulation of drilling fluid down the drill stem, out the bit, up the annular space between the pipe and the hole, and back to the surface. compare reverse circulation.

The process of pumping mud downward to the bit and back up tot he surface in a drilling or workover operation. see normal circulation, reverse circulation.

A lease or a number of leases of adjoining tracts of land that constitute a unit of acreage sufficient to justify the expense of drilling a wildcat.

1. a sudden increase in the drill bit’s rate of penetration. it sometimes indicates that the bit has penetrated a high-pressure zone and thus warns of the possibility of a kick.
2. a sudden increase in the rate of penetration during drilling. when this increase is significant (two or more times the normal speed, depending on local [...]

An individual or group of individuals that own a drilling rig and contract their services for drilling wells.

A specially compounded liquid circulated through the wellbore during rotary drilling operations. see mud.

1. intentional deviation of a wellbore from the vertical. although wellbores are normally drilled vertically, it is sometimes necessary or advantageous to drill at an angle from the vertical. controlled directional drilling makes is possible to reach subsurface areas laterally remote from the point where the bit enters the earth. it often involves the use [...]

An accessory employed above a packer, to permit annulus-to-tubing circulation or vice versa.