Oil & Gas Terms in Category M

Minimum curvature

A survey computation method that fits a 3-dimensional circular arc between two survey points.

The dogleg severity is constant through any section using this method, however, the build rate and turn rate, in general, are not.

Macaroni string

A string of tubing or pipe, usually 3/4 or 1 inch in diameter.


A light, gaseous, flammable paraffinic hydrocarbon that has a boiling point of -25 degrees f and is the chief component of natural gas and an important basic hydrocarbon for petrochemical manufacture.

Miniaturized completion

A well completion in which the production casing is less than 4.5 inches in diameter.

Compare conventional completion.


A common term for a rig weight indicator.

Martin-decker is the name of a company.


The fundamental unit of mass of a substance.

A mole of any substance is the number of grams or pounds indicated by its molecular weight.

For example, water has a molecular weight of approximately 18.

Therefore, a gram-mole of water is 18 grams of water; a poundmole or water is 18 pounds of water.

See molecular weight.

Mud pump

A large, high-pressure reciprocating pump used to circulate the mud on a drilling rig.

A typical mud pump is a two-cylinder, double-acting or a three-cylinder, single-acting piston pump whose pistons travel in replaceable liners and are driven by a crankshaft actuated by an engine or a motor.

Also called a slush pump.

Magnetic survey

An exploration method in which an instrument that measure the intensity of the natural magnetic forces existing in the earth’s subsurface is passed over the surface or through the water.

The instrument can detect deviations in magnetic forces, and such deviations may indicate the existence of an underground hydrocarbon reservoir.

Mop (lwd)

Abbr: mud operated pulse.


The evaluation of physical properties, usually including pressure, temperature and wellbore trajectory in three-dimensional space, while extending a wellbore.

Mwd is now standard practice in offshore directional wells, where the tool cost is offset by rig time and wellbore stability considerations if other tools are used.

the measurements are made downhole, stored in solid-state memory for some time and later transmitted to the surface.

Data transmission methods vary from company to company, but usually involve digitally encoding data and transmitting to the surface as pressure pulses in the mud system.

these pressures may be positive, negative or continuous sine waves.

Some mwd tools have the ability to store the measurements for later retrieval with wireline or when the tool is tripped out of the hole if the data transmission link fails.

mwd tools that measure formation parameters (resistivity, porosity, sonic velocity, gamma ray) are referred to as logging-while-drilling (lwd) tools.

Lwd tools use similar data storage and transmission systems, with some having more solid-state memory to provide higher resolution logs after the tool is tripped out than is possible with the relatively low bandwidth, mud-pulse data transmission system.

Mechanical loading arm (mla)

See marine loading arm.

Marine loading arm

A marine loading arm, also known as a mechanical loading arm, loading arm, or mla is a device consisting of articulated steel pipes that connect a tankship such as an oil tanker or chemical tanker to a cargo terminal.

genericized trademarks such as chiksan (often misspelled chicksan) are often used to refer to marine loading arms regardless of their manufacturer.

read also marine loading arm at wikipedia.

Miscible gas drive

Injection of a large volume of gas from an injection well where the gas is designed to lower the viscosity of the oil and help displace it towards the wellbore.

Mule shoe

A sub part of which is formed in the shape of a horseshoe and used to orient the drill stem downhole.

Mud weight recorder

An instrument installed in the mud pits that has a recorder mounted on the rig floor to provide a continuous reading of the mud weight.