VOLUME FOUR MUD CIRCULATION & TREATING EQUIPMENT

MUD SYSTEM OVERVIEW
Overview
The rig uses many pieces of equipment to circulate and treat or condition the mud.

Mud Tanks
Mud circulation begins here, in the mud tanks, sometimes called pits. Crew members prepare the mud in these tanks and make it ready for circulation

Mud Pumps
The heart of the circulating system is the mud pump. Often, rigs have two pumps, one primary pump and one for back up. Or, if hole conditions required, the driller can compound or combine the two pumps to circulate large volumes of mud. In fact, on deep wells, the rig may have three or four compound pumps. The powerful pump, or pumps, pick up mud from the mud tanks and send it to the drill string and bit. The pump moves the mud into the discharge line, up to standpipe and into the rotary hose.

Standpipe & Rotary Hose
The standpipe takes the mud about half way of the mast. The rotary hose is attached to the standpipe. The rotary hose is strong, flexible hose that moves with the swivel as it goes up and down in the mast. From the rotary hose, the pump moves mud through the swivel and then down the kelly and drill string. On rigs with a top drive, the mud moves through a passage in the top drive and then into the drill string.

Bit & Annulus
The pump moves the mud down the drill string to the bit. At the bit, the mud jets out of the openings or nozzles in the bit. The jets of mud move cuttings away from the bit. Mud then continues up the annulus, carrying the cuttings with it.

Return Line, Shaker & Mud tanks
From the annulus, the mud with the cuttings in it goes through the return line, sometimes called the Flow Line, to the shale shaker. The shale shaker removes the cuttings from the mud. The mud then falls into the mud tanks, where the mud pump can pick it up and continue the circulation process.

[TOOL BOX]: Arrange this circulating equipment in proper order, place the mouse around the component, click and hold on it and move it to its proper position. The mud pump is in position, what comes next?

MUD STORAGE, TANKS & RESERVE PIT
Overview:
Mud is made up at the rig location. Most rigs have several steel mud tanks. Mud and additives are mixed and held in the tanks. Some land rigs also have a reserve pit dug out of the ground. Mud tanks are also called mud pits, a carrier over from the days of earthen pits, mud tank is the preferred term. The rig does not necessarily use all the mud tanks at once, although it does use several. The active tanks hold mud the pump actively circulates.

Mud House
Often, mud components come to the rig in sacks. Normally, the crew stores the sacks in a special compartment called the mud house or sack room. The house or room keeps the sacks dry and allows them to be stored with care.

Bulk Tank
These silo-like tanks are bulk tanks or P-tanks. They hold mud additives like barite and bentonite. Crew members use some additives in such large quantities that suppliers load them into the bulk tanks to save time and money. Bulk tanks usually have their own hopper or pneumatic system for transferring the additives to the mud system.

Active Tank
The pump takes the mud out of the active mud tanks and circulates it through the system. Crew members connect the mud tanks with the piping and manifold. The number of active mud tanks depends on the amount of mud needed to keep the hole full, and the volume required on the surface to keep the mud in good condition for circulating.

Sand Trap
The sand trap is the tank directly below the shale shaker. The shale shaker removes most of the cuttings from the mud, but some are so small the shaker cannot trap them. These fall into the sand trap. The sand trap is the first settling tank. Crew members have to clean it regularly to remove the built-up solids.

Settling Tanks
Some small or old rigs may have two or more settling tanks in the tank system. They allow solids in the mud to settle out, but settling tanks do not do a very good job as compared with newer generation solids-removal equipment. So, today, most rigs use a dessander and desilter.

Reserve Tanks
Reserve tank is not a part of the active mud tank system, instead, the crew uses them to hold excess mud, or they may use them to mix a different type of mud in the pump’s currently circulating. They may also store heavy mud for emergency well control operations.

Slug Tank
A slug tank is a relatively small separate tank, or it may be a small separate part of a larger tank. The crew uses the slug tank to mix a slug. A slug is a small amount of heavy mud that is pumped down the string. Crew members may also use the slug tank to mix a small amount of mud for a special purpose. For example, the driller may need place or spot a small quantity of high viscosity mud, also called a pill, at some point down hole.

Suction Tank
The suction tank is where the mud pump picks up mud ready to circulate down hole. Mud in the suction tank should be clean, free of solids & gas, and be properly formulated or conditioned.

Chemical Tank
Crew members use the chemical tank to make special chemicals, such as caustic, that they will put into the active mud tanks.

Reserve Pit
On some land rigs, the rig owner digs a large pit next to the rig. This pit is called the reserve pit. The crew puts waste mud and run-off from the rig site in the reserve pit. In an emergency, they can also use it as a place to put more mud than the tanks can hold. Often, the rig operator lines the reserve pit with a thick plastic sheet to prevent liquids from leaching into the soil. And if the rig is on a migratory bird fly way, the operator covers it with a netting to keep the waterfowl from landing in it. Land rigs drilling in environmentally sensitive areas will not have a reserve pit. Instead, waste & run-off of a hole to an approved waste disposal area.

[TOOL BOX]: Here is your chance to be the driller’s assistant and carry out task to keep the mud system operating properly. For each task the driller gives you, click the location where the task will be carried out. When you select the right location, you’ll get your next instructions. See if you can carry out all five tasks before the timer runs out. Click “begin” when you’re ready to start.

MUD PUMPS
Over View
Powerful mud pumps pick up mud from the suction tank, and circulate the mud down hole, out the bit, and back to the surface. Although rigs usually have two mud pumps, and some times three of four, normally they use only one at a time. The others are mainly used as back up in case one fails. Sometimes however, the rig crew may compound the pumps. That is, they may use two, three or four pumps at the same time to move large volumes of mud when required. Rigs use one of two types of mud pumps: triplex pumps or duplex plumps. Triplex pumps have three pistons that move back & forth in liners; Duplex pumps have two pistons that move back & forth in liners. Triplex has many advantages: they weigh 30% less than a duplex of equal horsepower or kilowatts; the lighter-weighted parts are easier to handle, and therefore easier to maintain. The other advantages include: they cost less to operate, their fluid end is more accessible, and they discharge mud more smoothly, that is the triplex’s output does not surge as much as duplex. One of the most important advantages of triplex over duplex pumps is that they can move large volumes of mud at the higher pressure required for modern deep hole drilling. Triplex pumps are gradually phasing out duplex units.

Triplex Pump
In a triplex pump, the pistons discharge mud only when they move forward in the liner. Then when they move back, they draw in mud on the same side of the piston. Because of this, they’re also called “single-acting”. Single-acting triplex pumps pump mud at relatively high speeds. Input horsepower ranges from 220 to 2200 (from 164-1641 KW); large pumps can pump over 1100 gallons per minute (over 4000 liters per minute). Some big pumps have a maximum rated working pressure of over 7000 psi (over 50000KPa) with 5 inch (137 mm) liners.

Triplex Pump Operation
Here’s a schematic of a triplex pump. It has 3 pistons, each moving in its own liner. It also has 3 intake valves and 3 discharge valves. It also has a pulsation dampener in the discharge line. Look at the piston at left, it has just completed pushing mud out of the liner and through the open discharge valve. The piston is at its maximum point of forward travel; the other two pistons are at the other positions in their travel, also pumping mud. But right now, concentrate on the left one to understand how the pump works.
The left piston has completed its back stroke, drawing in mud through the open intake valve. As the piston moved back, it lifted the intake valve off its seat and drew mud in, a strong spring holds the discharge valve closed. The left piston has moved forward, pushing mud out through the now open discharge valve, a strong spring holds the intake valve closed. The left piston has completed its forward stroke, the full length of the liner, completely discharging the mud from it. All three pistons work together to keep a continuous flow of mud coming into and out of the pump. Crew member can change the liners and pistons, not only can they replace worn-out ones, but they can also install different sizes. Generally they use large liners and pistons when the pump needs to move large volumes of mud at relatively low pressure; they use small liners and pistons when the pump needs to move smaller volumes of mud at relatively high pressure.

[TOOL BOX]: You can control the position of the piston with your mouse to see how the triplex pump operates at any given point in this cycle.

Duplex Pump
In a duplex pump, the pistons discharge mud on one side of the piston and at the same time, taking in mud on the other side. Notice the top piston and liner. As the piston moves forward, it discharges mud on one side as it draws in mud on the other. Then, as it moves back, it discharges mud on the opposite side and draws in mud on the side where it earlier discharged. Duplex pumps are therefore double-acting. Double-acting pumps move more mud on a single stroke than a triplex, however, because they’re double acting, they have a seal around the piston rod. The seal keeps them from moving as fast as triplex. Input horsepower ranges from 190 to 1790 (or from 142-1335KW). The largest pump’s max. rated working pressure is about 5000psi (almost 35000KPa) with 6 inch (152 mm) liners.