NATURE OF DRILLING WASTE

It is obvious, from the preceding discussion, that drilling waste contains a large amount of base fluid, whether that fluid is diesel oil, mineral oil, oolefin, ester, or water. A more detailed discussion about the nature or characteristics of the waste should consider the place of disposal. In a broad sense, this can be accomplished by considering that all waste must be disposed in the water, on land, or in the air. For example, the characteristics of drilling waste when discharged offshore (disposal in
water) will be viewed from the potential effects between the waste and water. These are effects to the seabed, to the water column itself, and to the air/water interface at the surface. In this scenario, diesel oil is an obvious contaminant. Diesel oil creates a sheen on the water surface, disperses in the water column, and creates a toxic effect in cuttings piles on the seabed. For this reason, diesel oil-based drilling fluids and the cuttings generated while using them are not discharged into the sea.

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QUANTIFYING DRILLING WASTE

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.

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EXAMPLES FOR SOLIDS REMOVAL EQUIPMENT EFFICIENCY

What is the solids removal equipment efficiency?

This exercise involves the cost benefit of increasing solids removal equipment efficiency to 80% for the 4%vol drilled-solids concentration: With 80% removal efficiency and 1143 bbl of drilled solids reporting to the surface, 914 bbl would be discarded and 229 bbl returned to the pits. The drilling fluid needed to dilute the 229 bbl to 4%vol would require adding (229 bbl / 0.04), or 5725 bbl of new drilling fluid. This 5725 bbl would consist of 229 bbl of drilled solids and 5496 bbl of clean drilling fluid.

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CALCULATING THE DILUTION QUANTITY

The dilution required to compensate for the incorporation of 37.9 bbl of drilled solids was the 759 bbl of new mud, less the volume of the drilled solids in the new drilling fluid built, or 721 bbl. This is 19 bbl of dilution per bbl of incorporated solids (721.0 bbl / 37.9 bbl). The calculation for the dilution, that is, the volume of new mud that must be prepared, is

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