Description
Mud is the name given to drilling fluid which is mainly a mixture of water, or oil distillate, and ?heavy? Minerals such as Bentonite or Barites. Mud is pumped into a well at densities calculated to provide a hydrostatic pressure sufficient to overcome downhole formation pressures. (See e.g. Gas Kick). In addition, the mud is continuously circulated down to the bit, and returns in the annular space outside the drill-string, bringing with it rock cuttings for inspection and keeping the well clean. It is also engineered to maintain a thin protective layer of filter-cake on the bore hole wall, without excessive weight which would decrease the weight on the bit and hence penetration (see Drill String), and also possibly lead to differential sticking and formation damage. Mud is pumped from the mud pit (or tank) via the standpipe, rotary hose and gooseneck to the swivel, and into the drill stem. On return from down hole it is recovered and rock cuttings removed by the shale shakers before re-circulation. To Mud Up is to increase mud weight and downhole pressure. To Mud Off is to seal off a formation with heavy filter cake. A Mud Log is the record of mud make-up and analysis of cuttings recovered. The composition of mud used in a well is normally supervised by a Mud Engineer.
Source :
Alpha Thames Ltd 2004