Crude oil, natural gas liquids (NGLs) and water are stored in oil and gas fields. Unlike midstream tank farms at terminals and refineries, field storage consists of smaller vessels associated with oil, gas and water processing. Diesel generator fuel, potable water, and fire water are also stored offshore. NGLs are stored at atmospheric pressure in double-walled tanks.
Tank level monitoring can be provided with overflow control and alarm systems or shutdown pumps when level falls below the specified low level. Interface controls will sense the beginning of an oil/water interface during tank dewatering and control the water draw-off.
New recommended practices regarding tank overfill protection for above-ground storage tanks that receive Class I (flammable) liquids outline that careful selection and application of level controls can effectively protect against tank overfills.