Kosun Drilling Mud Tank in Drilling Fluids System

Sept. 13, 2012 - PRLog -- In directional drilling,  the drilling fluids are widely used with functions of providing hydrostatic pressure to downhole, controlling & maintaining the down hole pressure, keeping the drill bit cool and lubricating bit while it works, and most importantly, carrying out drill cuttings out of the well head to expand the lifetime of the drill bit.

Ⅰ· Summery Description

The drilling fluid, or called drilling mud, is made of many different kinds of chemical material, and can not just abandon them directly. That would be much harmful for the natural environment but also increase the drilling cost. So we have to introduce the solid control system. It separates the solids step by step through different stage of solid control equipments. Normally, in oil & gas drilling, the solid control system is consist of five stages: shale shaker, vacuum degasser, desander, desilter & centrifuge. Sometimes the desander & desilter can be combined as high efficient mud cleaner. One complete solid control system also includes mud tank, sand pump, mud mixer, agitator, vertical slurry pump, shearing pump, mud pump, mud gun etc.


The following table shows the different diameter of the solids that to be separated by different solid control equipments in the purification systerm


Ⅱ· How the Drilling Fluids Circulate in the mud tank.

For the working process of the solids purification equipments, please refer to the following sketch. First the mud pump sucks up the mud that kept in the mud tank, increase the pressure, and push it into the inner hole of the drilling stem through the swivel, and the mud would spray out through the drill bit nozzle, and meanwhile carry the solids that cut by the bit out of the borehole through the annulus of borehole and drilling stem, and then through the return line, the drilling mud comes to the solid control system to be treated.

Ⅲ· The Role of Mud Tank in Solid Control System
Mud tank plays an important role in the drilling fluid purification system. It is the carrier of the drilling fluid, and also the base of the above mentioned five stages purification equipments which all mounted on the top surface of the mud tank. For one single mud tank, it is normally divided into two or three different compartments, and the drilling mud would move from one compartment to another through different solid control equipments. And on the top surface of each compartment, there exists a mud agitator to prevent the mud from precipitating. And mud gun also works in the corner of the compartment play the same role of agitator through the high pressure mud.

There exists three or multi-nozzles on the top end of transfer pipe for the mud gun, and the nozzles canbe rotated for 360 degree, but normally 120 degree is complied in the common mud tanks. The mud gun is connected with one gate valve to control the flow of the mud that spay into the tank through the nozzles. The mud guns are light weight, small footprint and easy handling. The following, please refer to the technical Specification of mud gun that is is used in the mud tank:

As mentioned that one agitator is equiped on the top of each compartment, and the mud would be stirred by the agitator impeller which is welded with four 45-degree blads at the bottom end of the impeller. Driving by the agitator, the impeller can stirring the mud sufficiently.  The diameter of the impeller includes 600mm, 650mm, 700mm, 750mm, 800mm, 900mm & 1000mm, etc. While the length of the impeller shaft depends on the depth of the mud tank.

On the top of mud tank, there also exists a floating mark, the bottom of which is floated on the surface of the mud in the mud tank. By reading the mark, drilling workers can easily know the depth of the mud down in the tank, and no need to enter into the tank. While for the purpose of mud tank cleaning, and inner pipeline maintaining, there also exists a ladder in each compartment, and also a cover on the top to avoid any falling accident.

Ⅳ· How the Mud Tank Works.

The mud tank bears the whole circulation process of the drilling fluids between the wellhead and mud pump. First it comes directly to the shale shaker. The solids are to be separated by the shaker screen and discharged out of the mud tank through the sand-releasing slot, while the drilling fluid with small particles would enter down to the compartment below the shaker for further separation. If air infusion into the mud, a sand pump would suck up the mud from previous compartment  and pump it into the vacuum degasser to discharge the air in the mud and return the drilling mud into the second compartment. If non air infusion, the vacuum degasser would work as an agitator. For the third purification stage,  a sand pump would be used to suck up the drilling mud into the desander, after separate & discharge the solids, and the mud would enter again down into the third compartment. And the same for the desilter. And for the fifth stage of solid control system, a vertical slurry pump would be used to suck up the mud into the centifuge from the compartment that below the desilter. After separating & discharging, the drilling mud would enter again into the mud tank. and then sucked up by the mud pump into the down hole to recycle again.

v· How to make a mud tank.

According to the bottom shape difference, the mud tanks normally includes square shape tanks & ellipse tanks. According to the standards,
The mud tank is made of the steel plate & square tube, with the smooth cone-shape structure or the corrugated structure.  8mm thickness of the steel plate is required by the industrial standard on the tank bottom m, and 6mm for the side & top plates.The surface are made of slip-resistant steel plate. It also has walkway on the top made of also slip-resistant steel screen plate for workers to check & maintain the solid control equipments on the tank. And handrails that is made of steel square tubes are equipped on the edge of tank top surface, same as the steel stairs, which can be easily removed for transportation together with the tank. A water pipeline is also equipped on the top for cleaning the tank surface and equipments. The mud tanks also have cleanout opening to clean the sludge that precipitate in the tank. and the above mentioned five stage purification equipments are all mounted on the steel beam of the tank proof to maintain the stability of the system.

For the square tanks, the max. size could be 16000×3000×2400m. while the Standard Designs of the mud tank would be as following:

- 7500 × 2400 × 2000 mm
- 8000 × 2400 × 2000 mm
- 9000 × 2800 × 2200 mm
- 10000 × 2800 × 2500 mm
- 12000 × 2800 ×2500 mm
- 13000 x 2800 x 2500 mm

Ⅵ· How to Allocate the Mud Tank for the Drilling Rig.

According to its function in solid control system, the mud tanks include suction tank, agitator tank, storage tank, etc. The allocation of mud tank for the drilling rig depends on the depth of the well, and also the purification stage requirement. Normally, the first three solid control stages is completed on the tank No.1, which includes shale shaker, vacuum degasser, desander, while the fourth & fifth stages would be on the tank No.2, which means desilter & centrifuge, and the main function is for the centrifuge. While the other tanks will depends on the depth of the well, but also the mud demands of the drilling technique. Normally the large type drilling rig needs over 6 mud tanks.