The simplest drilling fluid is a dirty mixture of water and clay, often referred to as mud. The drilling fluid in the drilling process can be seen as the equivalent to the blood in the human body, the mud pump is the heart, and the drilled out shale (cuttings) represent the slag products. At the surface, we find the mud cleaning system which corresponds to the kidney and the lungs. In the mud cleaning system the cuttings are removed by means of a sieve, the shale shaker.