Disposal piles are large diameter (24- to 48-inch) open-ended pipes attached to the platform and extending below the surface of the water. Their main uses are to (1) concentrate all platform discharges into one location, (2) provide a conduit protected from wave action so that discharges can be placed deep enough to prevent sheens from occurring during upset conditions, and (3) provide an alarm or shutdown point in the event of a failure causing oil to flow overboard.
Most authorities having jurisdiction require all produced water to be treated (skimmer tank, coalescer, or flotation) prior to disposal in a disposal pile. In some locations, disposal piles are permitted to collect treated produced water, treated sand, liquids from drip pans and deck drains, and as a final trap for hydrocarbon liquids in the event of equipment upsets.
Disposal piles are particularly useful for deck drainage disposal. This flow, which originates either from rainwater or washdown water, typically contains oil droplets dispersed in an oxygen-laden fresh or saltwater phase. The oxygen in the water makes it highly corrosive and commingling with produced water may lead to scale deposition and plugging in skimmer tanks, plate coalescers, or flotation units. The flow is highly irregular and would thus cause upsets throughout these devices. Finally, this flow must gravitate to a low point for collection and either be pumped up to a higher level for treatment or treated at that low point. Disposal piles are excellent for this purpose. They can be protected from corrosion, they are by design located low enough on the platform to eliminate the need for pumping the water, they are not severely affected by large instantaneous flow rate changes (effluent quality may be affected to some extent but the operation of the pile can continue), they contain no small passages subject to plugging by scale buildup, and they minimize commingling with the process since they are the last piece of treating equipment before disposal.