SPE Members
Several of the processes used to reduce the environmental impact of drilling are counter-productive. They can increase drilling cost and often worse if the waste disposal problem rather than solving or relieving it. Two-stage centrifugation is probably the worst of these processes. The probably the worst of these processes. The trends toward total reliance on shale shakers for solids control, and the return of the liquid portion of hydroclone underflow to the system, in unweighted muds, are also very troublesome.
This paper reviews the importance of solids control and its relevance to waste management, discusses closed mud system and other methods of handling drilling fluid waste, and reviews the proper design, installation, and monitoring of the solids removal system.
The importance of solids control in oil well drilling has been clearly established by field and laboratory studies conducted over the past 35 years. Simply stated, drilling mud quality is the key to efficient drilling, and solids removal is the key to drilling mud quality. It is not coincidental that the companies with the most efficient drilling operations are those which devote the most attention to solids control.
With growing concern about protection of the environment, the use of closed mud systems has been. increasing. Some of the methods used to close these systems lead to reduced drilling fluid quality and -in the long run- to increased waste generation. Many important lessons about the relationships between solids control and drilling costs, learned since the introduction of hydroclones in the 50's, appear to have been forgotten. As a result, the use of counter-productive practices in the use of solids removal practices in the use of solids removal equipment is increasing. Three of these practices; double-centrifuging, the misuse practices; double-centrifuging, the misuse of "drying" shakers, and the removal of desanders and desilters alter improving shale shaker quality will be discussed in this paper.
The relationship between drilled solids and common drilling problems is clearly established. Excessive drilled solids concentration reduces filter cake quality, thereby increasing downhole filtration and cake thickness. This increases the likelihood of encountering unacceptable levels of torque and drag, stuck pipe, sloughing, and problems associated with increased surge and swab pressures. Also, and of much more importance, higher drilled solids contents significantly reduce rates of penetration, increasing drilling cost and the risk of wellbore instability caused by prolonged exposure of open hole intervals.
It has been proven that the adverse effects of drilled solids upon the drilling operation become more serious as the particle size decreases. Colloids, the finest solids, are the most damaging. Many of the solids generated by the bit enter the system as colloids, others become colloidal as they are circulated.
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