Stock tank oil
Open-knowledge reference entry
Stock tank oil is the volume of oil after flashing to nominal atmospheric (or other stated) storage pressure and temperature (as opposed to reservoir conditions).
Background
Crude oil is a complex mixture of many individual compounds which influence the physical properties of the oil, such as its density (API gravity), viscosity, Permeability, Dew point, Formation Volume, etc.. The properties also influence how the oil is classified and its value.
The quantity of oil originally in place in a reservoir is usually expressed as Stock Tank Oil Originally In Place (STOOIP), this is usually given in millions of stock tank barrels (MMstb).
Processing
Crude oil from subterranean reservoirs is usually produced with associated gas, produced water and solids such as sand. The crude oil must be stabilised to prevent excessive gassing during storage and to remove water and solids. Stabilisation involves passing the wellhead fluids through one, two, or three stages of separation operating at successively lower pressure to flash off lighter hydrocarbons and to remove water and solids. For a three stage train the operating pressures of the high, intermediate and low pressure separators might typically be:
HP separator: 1200 psig
IP separator: 200 psig
LP separator: 50 psig
Stock tank: 2 psig
The vapor pressure and relative volatility of constituent compounds is:
Alternatively, plant may be arranged with each stage operating at successively higher temperature.
The product is dead crude which is stored in stock tanks operating at just above atmospheric pressure. Offshore production also produces a dead crude but is often spiked with natural gas liquids (NGL) as a convenient transport route for these liquids.
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This entry incorporates text from “Stock tank oil” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.