A rig can either be cold- or hot-stacked;
Hot-Stacking
Hot-stacking of a rig, or ready-stacking as it often referred to, means that the rig is idle but operational. A Hot-stacked rig typically retains most of its crew and can deploy quickly if an operator requires its services. In a hot-stacked state, normal maintenance operations similar to those performed when the rig is active are continued by a crew so that the rig remains work ready. A crew needs to present on the rig on a daily basis to ensure that preservation and preventive maintenance schedules for drilling and general ship equipment are followed. Additionally, some machinery needs to run idle and/or under minimum load. For example, top-drive, drawworks, mud pumps, diesel engines, water-makers, compressors, deck cranes, and galley equipment as well.
Thus, a rig is kept in a hot-stacked state when its owner anticipates that the rig will be able to return to work shortly and should therefore be ready to be mobilized within a few days. Hot-stacked rigs are actively marketed and considered part of marketable supply.
Cold-Stacking
Cold-stacking of a rig is similar to “shuttering” an industrial plant – it involves “storing” the rig in a harbor, shipyard or designated area offshore and the crew is reduced to either zero or just a few key individuals and costs are therefore generally reduced to minimum levels. Typically, steps are taken to protect the rig including installing dehumidifiers and applying protective coatings to fight corrosion, installing monitoring systems that communicate rig status information to locations onshore and filling engines with protective fluids. Although the duration of cold-stacking can vary depending on many factors, rigs that are cold stacked are typically out of service for a significant period of time and are generally not considered to be part of marketable supply.
Before returning a cold-stacked rig to service, drilling contractors must hire a crew and some level of investment is usually required. The investment may come in the form of a survey, completing deferred maintenance or refurbishment
