By circulating continuously, the mud cools the drilling tool, helps to attack the rock by injection under pressure and cleans out the hole carrying away the pieces of crushed rocks. It is also indispensable for the maintenance of the borehole, insuring that the risk of collapse is avoided. The drilling mud is generally water-based with the addition of numerous products. First solid particles (often clays) used to increase the density. And then diverse chemical products used for properties adapted to the nature of the land being drilled and to ensure the stability of the mud. The density of the mud must be accurately calculated and precisely controlled. If it is too heavy, it is likely to penetrate at high speed into the reservoirs where the pressure is lower and the drilling is then in danger of “entering into losses” (instead of coming back up to the surface, the mud will disappear into the substratum). If it is too light, the water in the geological formations being drilled, at a higher pressure than that in the mud column, invades the hole and the drilling “enters into gains”. Unless the drilling team reacts very rapidly to this situation, the result can be an out-of-control eruption.
The composition of the mud is
specially adapted in each case, to the rock formations being drilled. The mud engineer, the “mud-man”, must continuously verify that it remains homogeneous and stable in its composition. He must also react very rapidly in the case of a problem and be ready to modify the composition of the mud as quickly as possible when required. Despite his name, which is not flattering, the “mud-man” has a very major responsibility on a drilling site! |