Oil and Gas Terms Beginning with “J”

A type of mechanism commonly used in the setting and unsetting of downhole tools and equipment such as packers. Most conventional downhole tools operate by upward or downward movement, rotation, or a combination of both. The J-slot profile creates the track for an actuating cam or pin that combines rotation and up or down movement to provide a simple yet reliable means of tool activation.

A type of mechanism commonly used in the setting and unsetting of downhole tools and equipment such as packers. Most conventional downhole tools operate by upward or downward movement, rotation, or a combination of both. The J-slot profile creates the track for an actuating cam or pin that combines rotation and up or down movement to provide a simple yet reliable means of tool activation.

Referring to the change in temperature observed when a gas expands while flowing through a restriction without any heat entering or leaving the system. The change may be positive or negative. For each gas, there is an inversion point that depends on temperature and pressure, below which it is cooled and above which it is heated. For example, for methane at 100oC [212oF], the inversion point occurs at about 500 atmospheres [7350 psi]. The magnitude of the change of temperature with pressure depends on the Joule-Thomson coefficient for a particular gas.The Joule-Thomson effect often causes a temperature decrease as gas flows through pores of a reservoir to the wellbore.

A support structure used to stabilize the injector head and pressure-control equipment on some offshore, or special onshore, coiled tubing units. The jacking frame is hydraulically controlled to enable the injector head to be located at a safe and secure working height. Additional features, such as the ability to skid the injector head to the side for access to the wellbore are included in some of the more complex designs of jacking frame.

A self-contained combination drilling rig and floating barge, fitted with long support legs that can be raised or lowered independently of each other. The jackup, as it is known informally, is towed onto location with its legs up and the barge section floating on the water. Upon arrival at the drilling location, the legs are jacked down onto the seafloor, preloaded to securely drive them into the seabottom, and then all three legs are jacked further down. Since the legs have been preloaded and will not penetrate the seafloor further, this jacking down of the legs has the effect of raising the jacking mechanism, which is attached to the barge and drilling package. In this manner, the entire barge and drilling structure are slowly raised above the water to a predetermined height above the water, so that wave, tidal and current loading acts only on the relatively small legs and not the bulky barge and drilling package.

A downhole tool used to deliver an impact force to the tool string, usually to operate downhole tools or to dislodge a stuck tool string. Jars of different designs and operating principles are commonly included on slickline, coiled tubing and workover tool strings. Simple slickline jars incorporate an assembly that allows some free travel within the tool to gain momentum for the impact that occurs at the end of the stroke. Larger, more complex jars for coiled tubing or workover strings incorporate a trip or firing mechanism that prevents the jar from operating until the desired tension is applied to the string, thus optimizing the impact delivered. Jars are designed to be reset by simple string manipulation and are capable of repeated operation or firing before being recovered from the well.

A qualitative pilot test used to determine whether water-wet solids (for example, barite) exist in an oil-base mud. An oil mud is put into a clean, round, glass quart jar filled about 1/3 full. The mud is stirred on a commercial-grade mixer or blender for 15 minutes. The mud is poured out and the jar, drained and examined. Solids strongly adhering to the glass are indicative of the presence of water-wet solids in the mud. The test has been correlated with inside plugging of drillpipe, which occurs when an oil mud becomes under-treated with oil-wetting agent. The electrical stability test cam be used to evaluate wettability and emulsion quality along with evidence of free water in high-pressure, high-temperature filtrate.

A small-diameter nozzle used to mix cement.

A downhole tool, generally run on wireline or coiled tubing, that uses the detonation of a shaped explosive charge to cut the surrounding tubing or casing wall. The cutting action leaves a relatively clean cut surface, although the explosive action tends to flare the cut ends, making retrieval of cut tubular difficult if the fishing tool engages on the external surfaces.

A mixing system used to mix dry powder materials with a base liquid, such as cementslurry or drilling muds. A funnel for the dry powder is mounted above a profiled bowl that incorporates one or more jets through which the liquid is pumped. The venturi effect created by the jets draws the powder into the turbulent stream, providing a rapid and efficient mixing action.

The use of shaped explosive charges to create perforation tunnels. The explosive charge produces an extremely high-pressure jet that penetrates the casing or liner to shoot into the reservoirformation. The shaped charges are contained in a perforating gun assembly that can be conveyed on wireline, tubing or coiled tubing, depending on the application and the wellbore conditions.

A type of pump that operates on the principle of a high-pressure fluid jet and the venturi effect it creates. Jet pumps are relatively inefficient but can tolerate a wide range of operating conditions, including easily handling sand-laden or abrasive fluids.

The exit velocity of the drilling fluid after it accelerates through bit nozzles.

A length of pipe, usually referring to drillpipe, casing or tubing. While there are different standard lengths, the most common drillpipe joint length is around 30 ft [9 m]. For casing, the most common length of a joint is 40 ft [12 m].

(noun) An archaic oilfield slang term for a geophone, the ground-mounted sensor used in seismic acquisition to detect and convert reflected seismic wave energy into electrical signals. The term originated in early seismic exploration when geophones were sometimes housed in jug-shaped containers.

Slang term for a member of a seismic acquisition crew or party who lays out cables and plants geophones for seismic acquisition and collects them after surveying.

Anything in the wellbore that is not supposed to be there. The term is usually reserved for small pieces of steel such as hand tools, small parts, bit nozzles, pieces of bits or other downhole tools, and remnants of milling operations.

A large, rectangular steel box, usually with sides made of expanded metal to facilitate seeing what is inside. The junk basket is used by the rig crew to store an assortment of relatively small parts of the drilling rig, ranging from drill bits to crossover subs to lifting subs to spare kellys. Dimensions vary, but a typical junk basket on a land rig is 8 ft wide [2.5 m] by 3 ft [1 m] deep by 30 ft [9 m] long.

A downhole tool similar in function to a casing scraper. A junk pusher is run to ensure an unobstructed wellbore before setting a packer or similar fullbore device.

A downhole tool with a profiled external surface designed to catch and retrieve junk or debris from the wellbore. The debris is carried up the tool-string annulus in the circulation fluid. An indented profile creating a larger annular area causes the fluid flow rate to drop and allows debris to drop into a basket or receptacle located at the base of the tool.