Drilling fluid not only helps the drilling rig into the well in the process of oil & gas drilling, but also has many functions. Just because of these, the safety and efficiency of drilling is assured well.

Now we will mention another one of the functions of drilling fluid: Control formation pressures

The drilling unit

If formation pressure increases, mud density should also be increased, often with barite (or other weighting materials) to balance pressure and keep the wellbore stable. Unbalanced formation pressures will cause an unexpected influx of pressure in the wellbore possibly leading to a blowout from pressured formation fluids.

Hydrostatic pressure = density of drilling fluid * true vertical depth * acceleration of gravity. If hydrostatic pressure is greater than or equal to formation pressure, formation fluid will not flow into the wellbore.

Well control means no uncontrollable flow of formation fluids into the wellbore.

Hydrostatic pressure also controls the stresses caused by tectonic forces, these may make wellbores unstable even when formation fluid pressure is balanced.

If formation pressure is subnormal, air, gas, mist, stiff foam, or low density mud (oil base) can be used.

In practice, mud density should be limited to the minimum necessary for well control and wellbore stability. If too great it may fracture the formation.

After being used, the drilling fluid commonly needs solids control equipment to be treated from one solids control equipment to next class of equipment, such as from shale shaker to vacuum degasser. Through disposing by a series solids control equipment, the drilling fluid can be available again for application in drilling.

The shale shaker is the first grade of solids control equipment in drilling purification system. It can remove cuttings above 75μm brought from the drilling well and the liquid with smaller particles will flow into tanks from where the fluid will flow into next grade solids control equipment to be treated.