Perforation in Oil Drilling

Briefly, a pit of oil can be described as a long hole in the subsoil, in decreasing diameters with depth from about 80 cm to about 15; cm, drilled up to a depth varying from a few hundred meters up to 6-8 km , the function of which is to communicate the layers in which hydrocarbon mixtures are accumulated with the surface.

For its perforation execution, depending on whether it is offshore or on-shore drilling , a dedicated drilling rig is mounted on a platform or directly on the ground. The most obvious part is a high metal tower up to about 60 meters, usually trellised. At the base of the tower there is a work area, called "probe plane", where there is a rotary table with the center a hole through which drilling tools are dropped. The hole in the hole fixes the so-called "square rod" (below which the subsequent drilling rods will be screwed on), which transforms the rotary movement of the rotating table into axial motion. The drilling rods are circular, inside grooves, and screwed together as the drilling falls deep. Drilling operations through the use of square rods are now considered obsolete as this system allowed to puncture only a length equal to that of a single drilling rod (just over 9 meters) at a time. Current drilling technology involves the use of a large "top drive" engine supported by a robust "hook" placed inside the tower and screwed on the first of three drilling rods (a "stand"). The top drive prints the rotation to the whole drum battery in well. This system allows to drill a length of three rods at a time without using the shaft change after a single perforated rod.

The bottom end of the last rod mounts the drill bit, consisting of three toothed rollers which rotate grinding the rock or a compact matrix fitted with tungsten carbide inserts or artificial diamond that work on the rock an abrasive action . Drilling speed is particularly affected by the type of rocks encountered and the depth of work. Generally, for a 2-3 km well drilling a few months are needed. A special mudis circulated inside the well, to cool the chisel and to remove the debris of "rocks". In addition, the mud has the function of avoiding the fall of the well walls by balancing the pressure of the fluids contained in the perforated rocks and preventing them from dangerously going back to the surface. The mud is pumped inside the cave auctions, flows at the chisel and goes back to the gap (called "annulus") between the rods and the shaft walls. Once returned to the surface, the mud is sifted through vibrating screens ("vibrating"), possibly degassed and put into circulation the well. The rock debris on the surface is examined by a team of geologists ("mud logging") that confirms or disproves predictions on the rocky area being pierced.