Technique of separating solids that occurred along with drilling fluids which got crushed by drill bit and came out on the surface of the well is called solids control.

System of solids control includes five stages consisting of vacuum degasser, mud tank, shale shake, desilter, desander, and centrifuge.

Big solids of diameter above 75 μm are separated by shale shaker, solids of diameter 45-74 μm by desander and desilter separates solids of 15-44 μm.

Combination of desander and desilter is probably used as efficient cleaner of mud. Air is separated by vacuum degasser during its entrance into drilling fluids. In absence of air, degasser works as big agitator.

These equipments are placed over mud tank when separation of solids from the mud is over then pumping of clean mud is done into the borehole

History of Development:

By using proper solids control techniques maintenance cost of drilling fluids, disposal and clean-up. cost can be minimized dramatically. In late nineteenth century oil industry realized the importance of these facts while separation of cutting from borehole was going on by using open earth pits.

Settling of solids due to gravity was allowed by the settling pits and series of weirs completed the process of solids control. To re-pump the clean mud down the hole, it is sent into the suction pump. This marks the beginning of using first solid control technique.
 

Introduction of shale shake in early 1930 signifies the innovation for oil industry.

Technologies applied in mining industry were used to derive shale shakers.

In today's world solids control is the basic solids control equipment used in oil industry.

Hydrocyclone or clone classifier was another machine used in 1930 hired from mining industry.

It works on the principle involving centripetal force that causes spinning of drilling fluids in the cone with high velocity compelling the settling of heavier soilds downward. Use of combination of drilling shale shaker with hydrocyclone becomes important part of solids control system.

Today’s solids control system includes formation of system of closed loop which permits enhancement in environment control and decrement of potential for drilling fluid spills.

United States and other several states contemplate on the application of closed loop system, mainly for operations of hydrocarbon fracturing.

Some Important Equipment:

Shale shaker is basic stage used in solids control system, separating cuttings of diameter above 75 μm by drilling fluids, pumped out from wells.

Desander is next stage after shale shaker used for separation solids diameter of 45 to 74 μm from previously treated fluids and sending them further from purification .

Desilter includes the separation of solids of diameter of 15 to 44 μm. After that treated fluid will go for processing.

Mud cleaner purpose is to eradicated solids having bigger size than barite. Removal of solids of diameter ranging from 74-105 μm is done by mud cleaner before than viscosity develops.

Separation of Mud and Gas by Mud Gas Separator.

Decanter centrifuge is used in drilling mud system for separating suspension of solids phase with particle diameter（d≥2 μm） for drilling mud circulation and drilling fluids recycling.