Many rigs use a combination of agitators and mud guns. To summarize
the preceding discussions on mechanical agitators and mud guns, a list of
pros and cons are presented to aid in the proper selection and application
of agitation equipment. The list is not necessarily complete but
will help both the designer and rig personnel consider both immediate
and long-term consequences of decisions.
Mechanical mud agitators may be supplemented with mud guns strategically
located to stir dead zones. Round tanks nearly eliminate these dead spaces and thus the need for mud guns and their supporting hardware (pumps, piping, valves, etc.), providing a simpler tank system. Additionally, round tanks demonstrate advantages over square or rectangular tank designs, such as:
. Ease of cleaning out
. Extra space in which to place piping and pumps
. No need for compartmentalization, since each tank is its own compartment
. Symmetrical design, ensuring mixing that is usually very good
With square or rectangular tanks, limitations on mechanical agitators
may make the inclusion of mud guns a necessity. For most instances,
there should be properly sized mechanical agitators to adequately stir
the tanks, and strategically placed mud guns to eliminate dead zones.
1. Pros of Mechanical Agitators
. Variety of gearbox and impeller combinations to suit most needs
. Effective on deep and large tanks
. Can be designed to induce more or less shear as needed
. Help cool mud by exposing more fluid to the atmosphere
2. Cons of Mechanical Agitators
. Cannot blend different tanks of mud or transfer mud between compartments
. Higher initial cost
. More surface space required than mud guns
. Heavier than mud guns
. Electricity is required (in most cases)
. Possible dead zones
. May require installation of baffles
3. Pros of Mud Guns
. Lower capital investment than mechanical agitators
. May use existing rig pumps (if there is sufficient pump capacity available)
. Flow may be concentrated to a given area to reduce or eliminate dead
spots
. Lower weight than mechanical agitators (excluding pump and piping)
. Can accelerate shear rates
. May be used to transfer and blend mud between tanks and/or compartments
4. Cons of Mud Guns
. If mud guns alone are used, there will be a need for many of them, with
significant pump and piping costs as well
. High-pressure surface nozzles may aerate mud
. Nozzle wear will cause higher flow, which requires more horsepower
and can lead to pump motor overload if nozzles are not replaced in time
. If solids have settled and a gun is directed toward the buildup, a slug of
solids can plug pumps, cones, and or centrifuges
. May increase requirements for solids-control equipment capacity and associated hardware
