The use of earthen or lined pits is integral to drilling waste management. During most China drilling operations, the drilling cuttings separated by the shale shaker are sent to a pit called the reserve pit located near the drill rig. The pit is generally open to the atmosphere, so it also accumulates stormwater and washwater from the rig.
The strategic location of small pits near drilling sites can also help minimize spillage of drilling waste. Unless site characteristics are such that no significant threat to water resources can occur, liners are generally required. Where pits must be constructed adjacent to water bodies or on sloping terrain, engineering precautions incorporated into the design will help to ensure pit integrity. Precautions should be taken to prevent disposal of chemicals, refuse, debris, or other materials not intended for pit disposal.
At the end of the drilling job, any hydrocarbon products floating on top of the pits are recovered and any free water or other liquids are collected and disposed of, usually in an injection well. The remaining cuttings are covered in place using native soils, the surface is graded to prevent water accumulation, and the area is revegetated with native species to reduce the potential for erosion and promote full recovery of the area's ecosystem. Reserve pits should be closed as soon as possible following the generally accepted closure procedures in the region.
For drilling waste with constituent concentrations only slightly higher than those allowed for traditional pit burial, the drilling waste may be blended with clean, local soil to dilute and reduce the high concentrations to acceptable levels before the drilling waste mix is buried. The objective of this approach is to incorporate drilling waste that meet required criteria into the soil at a level below the major rooting zone for plants but above the water table. Costs for such burial depend on the volume of soil required to be mixed to bring concentrations of oil and grease to within appropriate oil and grease limits, pit excavation costs, and loading/hauling costs of soils and drilling cuttings.
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