Solids Control –Solids Separation–Shale Shakers

Solids Separation

•Settling
–Settling pits are seldom used in modern drilling operations; however, they can be found from time to time.
–The rate of solids settling in settling pits or sand traps depends on
•Size, shape and specific gravity
•density of the drilling fluid
•viscosity of the drilling fluid
•type of fluid-flow regime
•residence time in the pit.
•Settling continued
–On a drilling rig with inferior shale shakers, a sand trap or settling pit will remove some of these large drill solids.
–Most modern shale shakers will remove sand-size and larger solids without the need for sand traps and/or settling pits.
•None of the solids-control equipment used in drilling will remove 100% of the solids generated.
•To compare the efficiency of solids-control equipment, a cut point particle-size rating is used.
–The cut point refers to the combination of a micron size and the percentage of that particle size removed.
•Cut point designations should include the percentage of the stated size removed.
–Cut points should always be denoted with the letter “D”with a subscript indicating the percentage removed.
–Without this percentage, no two cut point sizes can be compared.
–A D50cut point of 40 microns means that 50% of the 40-micron size particles have been removed and 50% have been retained in the mud system.

Shale Shakers

•The most important solids-control devices are shale shakers, which are vibrating screen separators used to remove drill cuttings from the mud •As the first step in the mud-cleaning/solids-removal chain, they represent the first line of defense against solids accumulation. •Shale shakers differ from other solids-removal equipment in that they produce nearly a 100% cut (D100) at the screen opening size. •Many potential problems can be avoided by observing and adjusting the shale shakers to achieve maximum removal efficiency for the handling capacity. •Using screens of the finest mesh to remove as many drill solids as possible on the first circulation from the well is the most efficient method of solids control. –It prevents solids from being re-circulated and degraded in size until they cannot be removed. –As much as 90% of the generated solids can be removed by the shale shakers •Unless the shale shakers are operating properly, and have screens of the finest mesh possible, all other equipment is subject to overloading and inefficient operation

•The mud flow should be spread over as much of the screen surface as possible by using feed-control gates located between the possum belly (flow line-to shaker transitional reservoir and the screen surface.
–The mud should cover 75% of the screens (About 1 foot from the end of the screens)