The fates of drill cuttings from offshore wells, and their effect on the marine environment, have been studied by means of side-scan sonar, scuba and underwater photography. Adverse effects are minimal and short-lived, and in some instances the accumulation of cuttings may be beneficial. Modification of normal mud and cuttings discharge procedures would be needed only in very unusual circumstances.
The extreme underbalance that results when drilling with air or gas allows large disc-shaped cuttings to break from the formation with the impact of the bit tooth. These cuttings are degraded to dust as the turbulent air lifts them to the surface. Solids control while air drilling (including natural gas and nitrogen) consists of controlling atmospheric pollution, collecting samples, and disposing of cuttings and liquids. Normally there is no recovery or reuse of the air or gas except for a few occasions in natural-gas drilling when the gas is recycled to the gas plant. An elaborate separator/cleaning/recompressing system is required to recycle the gas. It is usually more economical to flare the gas than to recover and clean it (see Figure 1.)
Cuttings dryers are sometimes referred to as secondary drying of cuttings.Cuttings dryer is the most widely used technology for safely handling drilling waste. Drilled cuttings with associated fluid from the rig solids-control equipment have been passed over a second drying shaker for a number of years. The recovery of oil-based drilling fluid coupled with a 10 – 25% reduction in disposal volume is usually easily justified and has become standard procedure in areas where so-called pitless drilling or closed loop systems are the norm. Generally, the secondary drying shaker is a four-panel screening device running at 7.0 – 7.3 G’s at the screen surface. Drilled cuttings from a drying shaker typically test between 8 and 12% base oil (NAF) by wet weight. This retention-oncuttings (ROC) figure is significantly higher than the current minimum allowed for offshore discharge in the United States and, increasingly, elsewhere around the world. Accordingly, there has been increased interest in lowering the ROC figure by the use of different types of drying equipment.