Drilling is carried out by a broach that rotates in a helical direction while a drilling fluid (mud) circulates through it towards the bottom of the well. Once at the bottom, the fluid exits through some holes of the broach towards the bottom and the annulus (space between the internal wall of the well and the external wall of the drill string), dragging the cuttings towards the surface of the geological formations traversed.
One of the main functions of drilling fluids is to seal the wellbore walls. This process occurs thanks to the action of laminar clay crystals that are suspended in the fluid, which, when they come into contact with a surface, immediately cover it, forming an insulating layer that protects the walls of the well.
This clay lining forms an insulating seal that prevents fluid leaks into aquifers, as well as from the aquifer to the well, or to adjacent formations.
Once the desired depth is reached, the string is removed from the survey with the drilling bit, and then a casing pipe, commonly called casing, is introduced into the well. The function of the casing is to case the well and create a mechanical column to prevent it from collapsing and isolate it.
To complete the isolation, cement is injected through the bottom of the hole, cement that ascends through the annular space located between the internal wall of the well and the external wall of the casing. Cement is specially formulated to protect and isolate all drilled formations from possible contact with fluids, high pressures and high temperatures.