Method for efficiently recycling water based drilling fluids has been developed. This recycling is conducted in a way beneficial both for the drilling fluid supplier and the operator. Contaminated fluid (slop) is brought back onshore for treatment and reusable fluids from the slop treatment are brought back into the drilling fluids.
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.).
Drilling waste consists of waste drilling fluid, drilled cuttings with associated drilling fluid, and, to a lesser extent, miscellaneous fluids such as excess cement, spacers, and a variety of other fluids. The amount of drilling waste depends on a number of factors. These include hole size, solidscontrol efficiency, the ability of the drilling fluid to tolerate solids, the ability of the drilling fluid to inhibit degradation or dispersion of drilled cuttings, and the amount of drilling fluid retained on the drilled cuttings.