Ozone environmental implications


Geothermal Drilling. Geothermal drilling presents one of the most challenging environments for corrosion control. During geothermal drilling the bottomhole temperatures can reach around 480°F (250°C). Therefore, drilling fluids and chemical additives, such as corrosion inhibitors, must withstand high temperatures (480°F) and pressures around 4,000 psi. High temperatures, coupled with corrosive fluids encountered in the formation, result in increased corrosion rates. Water and oil-based drilling muds can damage the producing zones. To minimize this formation damage, aerated muds and gaseous drilling fluids are used. However, these drilling fluids increase the potential for accelerated corrosion of drilling equipment. This is because of high concentrations of oxygen in fluids and increased fluid velocities over the metal surface. Another problem that can arise during drilling a geothermal well is lost circulation. Lost circulation can occur while drilling through highly fractured formations. This leads to a displacement influx of corrosive agents into the wellbore. It also results in loss of expensive drilling fluid and chemical additives, such as corrosion inhibitors. When fluid losses occur, aerated or gaseous drilling techniques can be used. With these techniques, hydrostatic head can be adjusted (i.e., lightened) to balance the formation pressure and, consequently, reduce fluid losses to the formation. Another method sometimes used is blind drilling or dry drilling. In blind drilling, the drilling fluid is slowly pumped down the drillpipe without it returning to the surface. In this procedure drill cuttings are expected to be carried with drilling fluids into the host circulation zone. However, it is important to pick up the drillstem at regular intervals of short distances. This will reduce the chance of drill cuttings stacking up or accumulating in the annular chamber space above the bit, leading to a stuck drillstem. Quite often these cuttings will plug the lost circulation zone, and the drilling fluid circulates back to the surface. This method of drilling is extremely expensive as the drilling rates are reduced and drilling fluids are lost. The technique does not provide any means of protecting the external surface of the drillpipe from corrosive environment. Therefore, if possible aerated mud or gaseous drilling should be considered over the technique of blind drilling. Nitrogen can be used to aerate the drilling fluid to reduce corrosion problems. It can also substitute for air in gaseous drilling to minimize corrosion problems if economically feasible [216].  [c.1339]


Chemistry of the elements (1998) -- [ c.608 , c.848 ]