Hydrocyclones are very effective classification devices which, as a result of centrifugal forces in the spinning fluid, cause solids to be separated at the underflow. Hydrocyclone is core part of mud cleaner, desander and desilter.

The benefits of efficient solids removal have been well documented.  Effective solids control is particularly important in soft, fast drilling formations which are found in many areas of the world. These surface formations are normally drilled with large diameter holes resulting in very heavy solids loading. To complicate matters worse, these formations are largely uncemented, resulting in much larger volumes of cuttings than actually drilled. Furthermore, these unconsolidated sands are often accompanied by gumbo sequences, both of which tend to blind shaker screens making the normal process of solids control much more difficult. For these cases, even the best shakers may only run fairly coarse mesh screens. Often, most of these solids are in the size range to be effectively removed by a hydrocyclone. As a result, hydrocyclones are one of the most effective methods to remove solids when drilling surface holes.

Even when fine mesh screens (such as a AP210 which makes a 78 micron d50 separation, Hoberock9 ) are used, a considerable amount of the solids drilled go through the screen. Desilters are capable of a d50 separation as fine as 15 to 30 microns and therefore may remove a large part of the remaining solids. Drilling between 7000 and 9000 ft (2134 and 2743 m) due to additional solids removal by hydrocyclones.

The main drawback with hydrocyclones is that the solids removed may be wetter than desired. For these cases, particularly in a closed mud system, it
is necessary to use a centrifuge to produce dry solids and return liquid back to the system. In this case, hydrocyclones may be used to concentrate solids so that the number of centrifuges or the size centrifuges may be reduced.

Hydrocyclones are simple and inexpensive devices which are capable of removing large amounts of drilled solids. In spite of the hydrocyclones simplicity of construction, their performance with respect to their dimensional parameters is not well understood.

Hydrocyclone with interchangeable pieces, which allowed all the dimensional parameters to be varied, was built. Hydrocyclone parameters are most important with respect to flow rate and performance. A total of 450 tests of hydrocyclone performance have been conducted using one drilling mud. Based on these tests, a mathematical regression model was written which parameterizes the data for the test mud. The results of this model is presented graphically. These tests have shown that there is an optimum set of hydrocyclone dimensions which provide maximum separation. For the test mud, the performance of an optimum hydrocyclone is at least 25% greater than desi1ters presently utilized in the oilfield today. Dimensions for a hydrocyclone with near optimum separation which have a flow rate of 50 gpm are also presented. Utilization of optimum hydrocyclones will result in significant savings due to increased penetration rates and lower mud costs.