Brian A England. This paper was first published in GE’s April 1979 edition.
In 1844 Robert Beart of Godmanchester, England, invented a fluid circulating rotary drilling process in which the cuttings produced by the bit were brought to the surface in an upward flowing column of water. In the early years of rotary drilling it was found that particles of native clay picked up from the formation formed a slurry which greatly improved the lifting capability of the drilling fluid — or Drilling Mud as it is popularly termed.
The conveying of the drilled cuttings to the surface is still an essential requirement but, in addition, the drilling fluid must perform other important functions such as cooling and lubricating the bit, reducing the torque required to turn the drill string, promoting hole stability, preventing caving and sloughing of unconsolidated formations, etc. To achieve these requirements the composition of the fluid may become quite complex and a wide range of additives (largely developed by the oil industry) is now available to the driller. The drilling fluid has become a major drilling tool and as such requires careful monitoring and control as the drilling proceeds.
The drilling fluid is, of course, only one of a number of variables in a well drilling operation. The drilling fluid properties, hydraulics, bit type, weight on bit and rotational speed are all interdependent factors. An alteration to any one of these will affect all the others.