M

Main bore

The main drill string where the subsequent directional operations or open hole operations start from. Side bores are pulled out from the main bore until they reach the desired depth. 
 

Making a trip

The operation that is repeated every time the bit needs changing. Also called round trip. 
 

Manifold

A pipe that makes it possible to split fluid or a gas flow into several single flows. A set of pipes and valves directing fluid. 
 

Marginal field

A field that does not look profitable at present. 
 

Master valve

A valve positioned on the christmas tree that controls all flowing from the well. The valve is of such importance; two master valves are usually fitted to the christmas tree. Also see christmas tree
 

MWD

Measurement While Drilling 
 

Median line

The parting point between the sectors of two nations in an area of the sea. 
 

Metric ton

1000 kilo = 2204,61 lbs. 
 

Midstream

The term is sometimes used to describe the activities in between upstream and downstream. It is usually applied in relation to the transport of crude and natural gas through a pipeline. 
 

Mist

Tiny particles of fluids in a gas. Mist usually generates a core that gasses condensate around and then become tiny, floating drops. 
 

Multilateral

The construction of two or more wellbores in one or more reservoirs with the purpose of directing and optimising the movement of fluids in the reservoir(s). The lateral bores are connected to a common main bore, stretching all the way to surface. Several levels within completion systems may be installed in a lateral well in order to enable it to produce from several areas simultaneously.

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