HF260D water well drilling rig in Poland

Drilling fluid

Drilling fluid is one of the most important phases of hydraulic rotary drilling and needs to be understood by all drillers. It is relatively simple to handle and control if a few simple rules are followed. 

We can have very complex and sophisticated mud controls but normally they are not necessary to the degree of oil well construction. I cannot overemphasize, however, the importance of good mud control. With it lies the success or failure of each well you drill. 

We should mention at this point that bentonite clays are difficult to mix and the use of a jet hopper is desirable. 

The idea of the drilling fluid being correct means its viscosity should be such that the proper sealing effect is maintained with as little invasion into the water bearing formations as possible. This is developed by having proper weights and viscosities. Once we have prepared our fluid to the recommended condition it is circulated in the bore hole and in so doing (the weight of the fluid being higher than the pressure of the formation) there is a tendency for the fluid to penetrate outward into the formations themselves. 

The fluid begins to form a wall of clay on the sides of the bore hole. In other words the formation itself filters out the clay particles and develops what we call a filter cake. The thickness of this cake is governed by the ability of the cake to retard water losses into the formations. If we maintain a relatively thin cake the water loss and formation contamination will be slight, however, a thick or deep penetrating cake is very hard to remove and thereby restricts or prevents flow from the formation into our finished well. 

We can begin the drilling of our well with a known fluid but one thing to always remember is that as we drill through native clays we have the mixing of same with our fluid and sometimes this contamination is very high. In order to maintain the type fluid with which we can construct the most efficient job we must perform tests on our fluid to know the qualities.