Abstract

The volume and type of solids in a drilling mud system can adversely affect mud properties, reduce penetration rates, cause damage to drilling equipment, and increase total drilling costs. Effectively controlling the solids content of the mud system is an important phase of an efficient and cost-effective drilling program. The three basic methods of removing solids are: dilution and/or displacement of whole mud, settling and mechanical solids-control equipment.

The dilution method increases the total volume of the circulating mud system by the addition of dilution water and/or base mud, reducing the relative volume occupied by drilled solids. The amount of dilution necessary to reduce the volume of drilled solids to the desired level may be calculated with the following formula:

Equation (Available In Full Paper)

The displacement method removes a portion of the active mud system containing drilled solids and replaces it with an equal quantity of fresh water or base mud, maintaining a constant circulating volume. The amount of displacement required to lower drilled solids to a specified level can be computed as follows:

Equation (Available In Full Paper)

In effect, both methods create a surplus of mud to lower the relative solids content of the system. This surplus mud, which must be discarded or stored, has certain economic costs. If dilution water or water having is expensive, the value of surplus mud high, or the disposal of the excess a problem these methods impact unfavorably on overall drilling costs.

The settling method, by itself, is a slow and inefficient process which takes place in a sand trap or settling tank. Settling rates of solids in a drilling mud may be increased by flocculating and viscosity reducing chemicals. The settling rate can also be enhanced mechanically by various centrifugal devices which increase gravity, accelerating the separation process.

Solids-Control equipment is the most effective method off Solid control. There are several types of equipment available; each designed to operate most efficiently given the characteristics of the particular fluid system and of the drilled solids influx from the formation. Properly designed and applied systems can approach optimum efficiency (where the removed of solids from the mud system equals the influx of drilled solids). All solids control on their size or specific gravity. Solids-control equipment being used today are shale shakers, desanders, defilers, hydro cyclone centrifuge, and bowl centrifuges. The size, capacity, and operating range of each is shown in Fig 1.

Drilled solids brought to the surface from the borehole are initially removed from the mud stream by a shale shaker's vibrating screen. The circulating volume of mud determines screen opening sizes which range from a 10×10 mesh to a 200×200 mesh. Most shakers on rigs utilize the 10 to 20 mesh size to remove large drill cuttings (normally 30 and 40 percent of all drilled solids). In recent years, some rigs have adopted modern-type shakers using finer mesh screens. These finer screens remove a higher percentage of drilled solids from the mud stream but are limited by circulating volume branding capacities.

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