Mud tank

Last updated April 26, 2019

A mud tank is an open-top container, typically made of square steel tube and steel plate, to store drilling fluid on a drilling rig. They are also called mud pits, as they were once simple pits in the earth.

In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. One of the functions of drilling mud is to carry cuttings out of the hole.

Mud tank structure

Mud tanks are divided into square tanks and cone-shaped tanks according to the shape difference of the tank bottom.

The body of the tank is made by welding the steel plate and section, using the smooth cone-shape structure or the corrugated structure. The mud tank surface and passages are made of slip resistant steel plate and expanded steel plate. The mud tanks are made of the side steel pipe, all of the structure can be folded without barrier and pegged reliably. The surface of the tank is equipped with a water pipeline for cleaning the surface and equipment on the tank, it uses soaked zinc processing for the expanded steel plate. The ladder is made of channel steel to take responsibility the body, the foot board is made of expanded steel plate. The two-sided guard rails are installed the safe suspension hook. The mud tank is designed to be in a standard shanty to prevent the sand and the rain. The pipeline is installed in the tank to preserve the warm air heat.

Pipeline transport is the long-distance transportation of a liquid or gas through a system of pipes—a pipeline—typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than 2,175,000 miles (3,500,000 km) of pipeline in 120 countries of the world. The United States had 65%, Russia had 8%, and Canada had 3%, thus 75% of all pipeline were in these three countries.

The tanks are generally open-top and have walkways on top to allow a worker to traverse and inspect the level of fluids in the tanks. The walkways also allow access to other equipment that is mounted on the top. Recently, offshore drilling rigs have closed-in tanks for safety. The mud tank plays a critical role in mechanically removing destructive solids and sediment from costly land and offshore drilling systems.

A tank is sectioned off into different compartments. A compartment may include a settling tank, sometimes called a sand trap, to allow sand and other solids in the drilling fluid to precipitate before it flows into the next compartment. Other compartments may have agitators on the top, which have long impellers below inserting into the tank and stirring the fluids to prevent its contents from precipitating. And mud guns are often equipped at the corners of the tanks' top, spraying high-pressed mud to prevent the drilling fluids in the corner of the compartment from precipitating, typically for the square tanks.

The piping linking the mud tanks/pits with the mud pumps is called the suction line. This may be gravity fed or charged by centrifugal pumps to provide additional volumetric efficiency to the mud pumps.

The role of mud tank for solids control

Mud tanks play an important role in a solids control system. It is the base of solids control equipment, and also the carrier of drilling fluids. Solids control equipment that are all mounted on the top of mud tanks include the following:

Solids control is a technique used in a drilling rig to separate the solids in the drilling fluids that are crushed by the drill bits and carried out of the well surface. Normally, a solid control system contains five stages: the mud tank, shale shaker, vacuum degasser, desander, desilter, and centrifuge. The shale shaker is used to separate big solids with diameter above 75μm, the desander addresses solids from 45-74μm, and the desilter segregates solids between 15-44μm. Sometimes the desander and desilter are combined as one high efficiency mud cleaner. When air enters the drilling fluids, a vacuum degasser is used to separate the air. When there is no air in the mud, the degasser works as a big agitator. All these stages are mounted on the top of the mud tank. After separating the solids, the clean mud can be pumped into the borehole again.

A degasser is a device used in drilling to remove gasses from drilling fluid which could otherwise form bubbles.

Desanders and desilters are solid control equipment with a set of hydrocyclones that separate sand and silt from the drilling fluids in drilling rigs. Desanders are installed on top of the mud tank following the shale shaker and the degasser, but before the desilter. Desander removes the abrasive solids from the drilling fluids which cannot be removed by shakers. Normally the solids diameter for desander to be separated would be 45~74μm, and 15~44μm for desilter.

A centrifuge is a piece of equipment that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis of spin (outward) that can be very strong. The centrifuge works using the sedimentation principle, where the centrifugal acceleration causes denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and move to the center. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top.

Drilling fluids flow into the shale shaker directly after it returns to the surface of the well, and the solids that are removed by the screen would be discharged out of the tank, and the drilling fluids with smaller solids would flow through the screen into mud tank for further purification. A centrifugal pump sucks the shaker-treated fluids up to the desilter or mud cleaner for further purification. And vertical slurry pump is used to pump the drilling fluids up to the centrifuge, and a mud pump would pump the drilling fluids from mud tank into the borehole after it is treated by centrifuge and the circulation system continues.

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.

The number of the mud tanks that are needed on the drilling rig depends on the depth of the well, and also the mud demands of drilling. Normally the shale shaker and vacuum degasser and desander are mounted together on the same mud tank as the first tank at the oilfield, while desilter and centrifuge on the second tank. Also, the drilling rig has other different tanks such as a reserve tank, emergency tank, etc.

The classification of mud tank

Mud tanks are an important part in the solids control system. Based on functions, mud tanks include metering tanks, circulating tanks, chemical tanks, aggravating tanks, precipitating tanks, storing tanks, etc. ^[1]^[2]

Related Research Articles

A hydrocyclone is a device to classify, separate or sort particles in a liquid suspension based on the ratio of their centripetal force to fluid resistance. This ratio is high for dense and coarse particles, and low for light and fine particles. Hydrocyclones also find application in the separation of liquids of different densities.

A drilling rig is a machine that creates holes in the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and such are called augers. Drilling rigs can sample subsurface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures. The term "rig" therefore generally refers to the complex equipment that is used to penetrate the surface of the Earth's crust.

A mud engineer works on an oil well or gas well drilling rig, and is responsible ensuring the properties of the drilling fluid, also known as drilling mud, are within designed specifications.

The Derrickhand or Derrickman is the person who sits atop the derrick on a drilling rig. Though the exact duties vary from rig to rig, they almost always report directly to the driller. Their job is to guide the stands of the drill pipe into the fingers at the top of the derrick. Other duties might include monitoring pH and calcium levels, viscosity and the mud weight (density), adding chemicals and oil based fluids, and being responsible for the shale shakers and mud pump.

Shale shakers are components of drilling equipment used in many industries, such as coal cleaning, mining, oil and gas drilling. They are the first phase of a solids control system on a drilling rig, and are used to remove large solids (cuttings) from the drilling fluid ("mud").

Directional Boring, also referred to as Horizontal Directional Drilling (HDD), is a minimal impact trenchless method of installing underground utilities such as pipe, conduit, or cables in a relatively shallow arc or radius along a prescribed underground path using a surface-launched drilling rig. Directional Boring/HDD offers significant environmental advantages over traditional cut and cover pipeline/utility installations. The technique is routinely used when conventional trenching or excavating is not practical or when minimal surface disturbance is required.

In metallurgical processes tank leaching is a hydrometallurgical method of extracting valuable material from ore.

In the oil industry, mud weight is the density of the drilling fluid and is normally measured in pounds per gallon (lb/gal) (ppg) or pound cubic feet (pcf). In the field it is measured using a mud scale or mud balance. Mud can weigh up to 22 or 23 ppg.

A flow line, used on a drilling rig, is a large diameter pipe that is connected to the bell nipple and extends to the possum belly and acts as a return line,, to the mud tanks.

Squeeze job, or squeeze cementing is a term often used in the oilfield to describe the process of injecting cement slurry into a zone, generally for pressure-isolation purposes.

Cementing Equipment includes various items used while drilling oil/gas/water wells.

Effective solids control can be attributed to the overall performance of all the components of the mud systems. Conditioning the drilling fluid with the goal of dramatically lowering maintenance cost, avoiding excessive chemical treatment and maintaining mud systems volume will decrease the chance of equipment failure, unnecessary high mud costs, hole and drilling problems.

Mud Gas Separator is commonly called a gas-buster or poor boy degasser. It captures and separates the large volumes of free gas within the drilling fluid. If there is a "kick" situation, this vessel separates the mud and the gas by allowing it to flow over baffle plates. The gas then is forced to flow through a line, venting to a flare. A "kick" situation happens when the annular hydrostatic pressure in a drilling well temporarily falls below that of the formation, or pore, pressure in a permeable section downhole, and before control of the situation is lost.

A mud gun is designed for use in a solids control system of a drilling rig. It is a tool which is mainly used for mixing drilling mud in the circulatory system and to prevent the mud from precipitating. The structure of equipment is simple offering flexible operation and easy use. A mud gun is commonly used to guard against precipitates in a solids control system. The mud gun is installed in a mud tank.

A centrifugal water–oil separator, centrifugal oil–water separator or centrifugal liquid–liquid separator is a device designed to separate oil and water by centrifugation. It generally contains a cylindrical container that rotates inside a larger stationary container. The denser liquid, usually water, accumulates at the periphery of the rotating container and is collected from the side of the device, whereas the less dense liquid, usually oil, accumulates at the rotation axis and is collected from the centre.

References

↑ "The classification of mud tank". DC solids control. 25 May 2013.
↑ "Tanks in solids control system". Aipu Solids control. Apr 15, 2014.

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[1] "The classification of mud tank". DC solids control. 25 May 2013.

[2] "Tanks in solids control system". Aipu Solids control. Apr 15, 2014.