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SUSPEND AND RELEASE CUTTINGS

 

Drilling muds must suspend drill cuttings, weight materials and additives under a wide range of conditions, yet allow the cuttings to be removed by the solids-control equipment. Drill cuttings that settle during static conditions can cause bridges and fill, which in turn can cause stuck pipe or lost circulation. Weight material which settles is referred to as sag and causes a wide variation in the density of the well fluid. Sag occurs most often under dynamic conditions in high-angle wells, where the fluid is being circulated at low annular velocities.

High concentrations of drill solids are detrimental to almost every aspect of the drilling operation, primarily drilling efficiency and ROP. They increase the mud weight and viscosity, which in turn increases maintenance costs and the need for dilution. They also increase the horsepower required to circulate, the thickness of the filter cake, the torque and drag, and the likelihood of differential sticking.

Drilling fluid properties that suspend cuttings must be balanced with those properties that aid in cutting removal by solids-control equipment. Cuttings suspension requires high-viscosity, shear-thinning thixotropic properties, while solids-removal equipment usually works more efficiently with fluids of lower viscosity. Solids-control equipment is not as effective on non-shear-thinning drilling fluids, which have high solids content and a high plastic viscosity.

 

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For effective solids control, drill solids must be removed from the drilling fluid on the first circulation from the well. If cuttings are recirculated, they break down into smaller particles that are more difficult to remove. One easy way to determine whether drill solids are being removed is to compare the sand content of the mud at the flow line and at the suction pit.

 

Notes on the text:

 


Date: 2015-01-12; view: 1015


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