Mechanical solids control and related equipment

Oct. 18, 2012 - PRLog -- The goal of modern solids control systems is to reduce overall well costs by prompt, efficient removal of drilled solids while minimizing the loss of liquids. Since the size of drilled solids varies greatly — from cuttings larger than one inch in diameter to submicron size — several types of equipment may be used depending upon the specific situation. The fundamental purpose for solids removal equipment is just that — removes drilled solids. The end result is reduced mud and waste disposal costs.

To reach this goal, each piece of equipment will remove a portion of the solids, either by screening or centrifugal force. Each type of equipment is designed to economically separate particles of a particular size range from the liquid. Also to operate effectively, each type of equipment must be sized, installed, operated, and maintained properly.

The efficiency of the solids control system can be evaluated by comparing the final volume of mud accumulated while using the equipment to the volume of mud that would result if drilled solids were controlled only by dilution. The overall results of solids removal can be monitored by the use of flow meters to determine the actual mud volume built.

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The efficiency of solids removal equipment and/or systems used can be evaluated in two ways:

1) Efficiency of drilled solids removal,
2) Efficiency of liquid conservation.

The greater percentage of drilled solids removed, the higher the removal efficiency. The higher the solids fraction of the waste stream, the better. Both aspects should be considered.

For example, a desilter usually does well at removing solids but at the cost of significant losses of liquid; sometimes 80% of the volume of the waste stream will be liquid. By contrast, a properly operating shale shaker or centrifuge typically removes 1 barrel or less of mud with each barrel of solids. Most remaining equipment delivers a lesser degree of dryness than do the shakers or centrifuges.

Most solids control systems include several pieces of equipment connected in series. Each stage of processing is partly dependent upon the previous equipment functioning correctly so as to allow the next stage to perform its role. Should one piece of equipment fail, the equipment downstream will soon lose efficiency or fail completely.

The first piece of equipment used to separate the solids from the mud is usually a vibrating screen or series of screens. The cuttings that are larger than the mesh openings are removed by the screen but carry an adhered film of mud. The screen mesh should be sized to prevent excessive losses of whole mud over the end screen.

The second step is to remove the sand-sized, silt sized and larger clay particles that were not removed in the shakers by using hydro cyclones. Hydro cyclones with a cone diameter of 6 to 12 inches are called desanders, and hydro cyclones with a cone diameter of less than 6 inches are called desilters. These units should normally be sized to process 125% of the maxi-mum flow rate used to drill.  Sometimes a screen is used below a hydro cyclone to “dry-out” the cone’s discharge to minimize the loss of fluid. The hydro cyclone and vibrating screen device is called a mud cleaner or mud conditioner. If a location must be “pitless”, then the screens are essential to minimize the liquid waste volume.

The final step may be to remove the ultrafine silt and clay-sized solids with the use of a decanting
Centrifuge. On a weighted mud, two centrifuges may be used in series: the first to salvage barite, the second to remove fine solids and reclaim the valuable liquid phase.

Any questions, please contact us for more information.
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