Adverse effects caused by drilled solids account for a major portion of drilling fluid maintenance expenditures. Drilled solids are the number one contaminant of all drilling fluids. Considering that a 12¼ in. gauge hole drilled to 10,000 ft would result in 1,327,000 lb or more of drilled solids, the above statement is not surprising.
A special case of liquid/gas fluid is the diesel/nitrogen or synthetic-oil/ nitrogen mixture. These systems have low viscosities and are used primarily in reentries or horizontal slim holes. They tend to require more fluid than water-based fluid systems. Annular velocities of 150–200 ft/ min are common in the horizontal section of the hole. In the drilling of slim holes, hole volumes are less than they are in the drilling of conventional holes, but strong surging occurs. A closed pressurized separator system is used when drilling with an oil/gas system (Figure 19.1.).
Net Positive Suction Head ( NPSH ) is extremely important to the operation of a centrifugal pump. Factors that affect NPSH are atmospheric pressure, suction line friction loss, elevation, fluid temperature and SG.
The %vol low-gravity solids can also be calculated from the average specific gravity (ASG) of the solids in the sample: