The Circulation System - drilling engineering

 

The Circulation System

The circulating system provides the equipment, materials and working areas to prepare,

maintain  and  condition  the  drilling  fluid.  There  are  three  main  components  of  the

circulating system:

1. The drilling fluid

2. The circulating equipment

3. The conditioning area

The circulation equipment basically consists of:

1. Suction mud pit: A steel container used to hold and control drilling fluid.

2. Mixing hopper: A device used to rapidly add solid materials to the drilling fluid.

3. Suction line: A line which connects the mud pit and the mud pump.

4. Pump discharge line: A line which carries the drilling fluid to the standpipe.

5. Standpipe: A steel pipe clamped vertically to the side of the derrick. It is fitted with a

    goose-neck where the rotary hose is attached.

6.  Rotary  hose: A  strong  and  flexible  rubber  hose  that connects  the  standpipe  to  the

     swivel. Its  function is  to deliver  high  pressure muds from  the  stand  pipe  to the  swivel 

     while allowing the movement of the swivel up and down the mast.   

7. Drill stem: This includes the swivel, kelly or top drive system, drill string and bit.

8. Annulus: The space between the drill stem and the wellbore wall.

9. Return line: This line carries the drilling fluid by gravity from the wellbore to the

    conditioning area.

10. Setting tanks: These are steel containers used to hold the drilling fluid during

     conditioning. They are also known as sand traps.

11. Conditioning equipment: This includes equipment used to clean up the drilling fluid 

      after it has been brought up from the wellbore.

12.  Mud  pumps:  The  mud  pumps  are  the  heart  of  the  circulating  system,  providing 

      power to move the fluid at the required pressure and volume. 

1. Mud Pumps:

This is the heart of the circulation system. The rig often has 2 pumps, one is a

primary pump and the other is a back-up pump. However, it is possible to

compound the two pumps to deliver high mud volume required to drill deep wells.

There are two basic types of mud pumps:

1. Triplex pumps: Have three pistons that move back and forward in liners. The

triplex pumps generally are single-acting pumps that pump only on the forward

piston strokes.

2. Duplex pumps: Have two pistons that move back and forward in liners. The

duplex pumps generally are double-acting pumps that pump on both forward and

backward piston strokes.

The triplex pumps have the following advantages over the duplex pumps:

1. Triplex pumps are lighter and more combated.

2. Easy to operate and maintain.

3. Discharge mud more smoothly (Less surge)

4. Have the ability to move large volume of mud at high pressure.

Shale Shaker

The  drilling  fluid  comes  directly  to  the  shale  shaker  from  the  wellbore.  Its  primary 

function is to remove larger cuttings and broken formation pieces from the drilling fluid.

This  is  done  by  moving  the  drilling  fluid  over  vibrating  screens  that  separate  the 

unwanted cuttings. Shale  shakers  and can effectively  remove up  to 80% of  all  solids 

from a drilling fluid, if the correct type of shaker is used and run in an efficient manner. 

 Desander

The desander consists of a number of cone-shaped cylinders that remove smaller solid 

particles that pass through the shale shaker screens. The drilling fluid is forced through 

the  cylinder    under  pressure (Desanders  work  on  the  principals  of  centrifugal  forces 

inside  the  hydro-cyclone))  with  the  heavier  particles  being  removed  and  discharged 

through the bottom by centrifugal force. Desanders are primarily used when drilling with 

water based muds to help maintain low mud weights. Desanders should never be used 

with oil based muds, because of  its very  wet solids discharge.The desander makes a 

cut in the 40 to 45 micron size range with a spray discharge. 

Desilter:

The desilter is similar to the desander in operation and function except that the desilter

can remove very minute formation particles from the drilling fluid (20 to 25 micron size).

Desilters also should never be used with oil based muds

Vacuum Degaser

Its function is to remove gases from the drilling fluid because gases:

1. Reduce density of the drilling fluid.

2. Reduce pump efficiency.

3. Decrease hydrostatic pressure in the well.

4. Increase drilling fluid volume.

Mud Gas Separator

It is a container that is attached to the choke manifold by high-pressure lines. Its primary 

functions are to:

1. Eliminate larger quantities of free gases entrained in the drilling fluid.

2. Save any usable fluid by returning it to the degasser.

3. Pipe any flammable and/or poisonous gases to a safe distance away from the rig.