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Stock tank oil refers to the volume of oil after flashing to nominal atmospheric (or other stated) storage pressure and temperature (as opposed to reservoir conditions).
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. [1]
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). [2]
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. [3] 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: [4]
The vapor pressure and relative volatility of constituent compounds is: [4]
| Component | Vapor pressure at 100°F, psia | Relative volatitity |
|---|---|---|
| C1 (methane) | 5000 | 96.9 |
| C2 (ethane) | 800 | 15.5 |
| C3 | 190 | 3.68 |
| iC4 | 72.2 | 1.40 |
| nC4 | 51.6 | 1.00 |
| iC5 | 20.4 | 0.40 |
| nC5 | 15.6 | 0.30 |
| C6 | 5.0 | 0.10 |
| C7+ | 0.1 | 0.00 |
| CO2 | - | infinite |
| N2 | - | infinite |
| H2S | 394 | 7.64 |
Alternatively, plant may be arranged with each stage operating at successively higher temperature. [4]
The product is dead crude which is stored in stock tanks operating at just above atmospheric pressure. [3] Offshore production also produces a dead crude but is often spiked with natural gas liquids (NGL) as a convenient transport route for these liquids. This is known as live crude. The NGL is flashed off and recovered in the onshore separation plant. The operating pressure and temperature of the separation plant may be specified such that the oil meets a required vapor pressure, such as Reid Vapor Pressure. [3]
Density and viscosity are important property inputs into correlations for pipe-flow calculations. Stack Tank Oil (STO) density (or API) may also be used by regulatory bodies to classify oil and oil products. Other properties such as Molecular Weight, saturated aromatic resin and asphaltene (SARA), refractive index, wax appearance temperature, asphaltene precipitation, and acid number, are also specified at Stock Tank conditions. [1] Typically stock tank conditions are 14.7 psia and 60°F (101,325 Pa and 16°C).Flowrates of oil are commonly specified at Stock Tank conditions, e.g: Stock Tank barrels of oil per day STBOPD.
Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natural gas will condense to a liquid state if the temperature is reduced to below the hydrocarbon dew point temperature at a set pressure.
A visbreaker is a processing unit in an oil refinery whose purpose is to reduce the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons.. The process name of "visbreaker" refers to the fact that the process reduces the viscosity of the residual oil. The process is non-catalytic.
Heavy crude oil is highly viscous oil that cannot easily flow from production wells under normal reservoir conditions.
Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and saturates. The word "asphaltene" was coined by Boussingault in 1837 when he noticed that the distillation residue of some bitumens had asphalt-like properties. Asphaltenes in the form of asphalt or bitumen products from oil refineries are used as paving materials on roads, shingles for roofs, and waterproof coatings on building foundations.
An oil terminal is an industrial facility for the storage of oil, petroleum and petrochemical products, and from which these products are transported to end users or other storage facilities. An oil terminal typically has a variety of above or below ground tankage; facilities for inter-tank transfer; pumping facilities; loading gantries for filling road tankers or barges; ship loading/unloading equipment at marine terminals; and pipeline connections.
In the upstream oil industry, a gas–oil separation plant (GOSP) is temporary or permanent facilities that separate wellhead fluids into constituent vapor (gas) and liquid components.
The Ninian Central Platform is an oil platform in the North Sea. When constructed in Loch Kishorn, Scotland in 1978 the 600,000 tonne platform was the world's largest man-made movable object before being towed to its current position and sunk to the sea floor.
A turboexpander, also referred to as a turbo-expander or an expansion turbine, is a centrifugal or axial-flow turbine, through which a high-pressure gas is expanded to produce work that is often used to drive a compressor or generator.
Natural-gas processing is a range of industrial processes designed to purify raw natural gas by removing contaminants such as solids, water, carbon dioxide (CO2), hydrogen sulfide (H2S), mercury and higher molecular mass hydrocarbons (condensate) to produce pipeline quality dry natural gas for pipeline distribution and final use. Some of the substances which contaminate natural gas have economic value and are further processed or sold. Hydrocarbons that are liquid at ambient conditions: temperature and pressure (i.e., pentane and heavier) are called natural-gas condensate (sometimes also called natural gasoline or simply condensate).
An oil production plant is a facility which processes production fluids from oil wells in order to separate out key components and prepare them for export. Typical oil well production fluids are a mixture of oil, gas and produced water. An oil production plant is distinct from an oil depot, which does not have processing facilities.
The term separator in oilfield terminology designates a pressure vessel used for separating well fluids produced from oil and gas wells into gaseous and liquid components. A separator for petroleum production is a large vessel designed to separate production fluids into their constituent components of oil, gas and water. A separating vessel may be referred to in the following ways: Oil and gas separator, Separator, Stage separator, Trap, Knockout vessel, Flash chamber, Expansion separator or expansion vessel, Scrubber, Filter. These separating vessels are normally used on a producing lease or platform near the wellhead, manifold, or tank battery to separate fluids produced from oil and gas wells into oil and gas or liquid and gas. An oil and gas separator generally includes the following essential components and features:
Onshore, when used in relation to hydrocarbons, refers to an oil, natural gas or condensate field that is under the land or to activities or operations carried out in relation to such a field.
An API oil–water separator is a device designed to separate gross amounts of oil and suspended solids from industrial wastewater produced at oil refineries, petrochemical plants, chemical plants, natural gas processing plants and other industrial oily water sources. The API separator is a gravity separation device designed by using Stokes Law to define the rise velocity of oil droplets based on their density and size. The design is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water. The suspended solids settles to the bottom of the separator as a sediment layer, the oil rises to top of the separator and the cleansed wastewater is the middle layer between the oil layer and the solids.
In chemical engineering, a vapor–liquid separator is a device used to separate a vapor–liquid mixture into its constituent phases. It can be a vertical or horizontal vessel, and can act as a 2-phase or 3-phase separator.
Crude oil is extracted from the bedrock before being processed in several stages, removing natural contaminants and undesirable hydrocarbons. This separation process produces mineral oil, which can in turn be denoted as paraffinic, naphthenic or aromatic. The differences between these different types of oils are not clear-cut, but mainly depend on the predominant hydrocarbon types in the oil. Paraffinic oil, for example, contains primarily higher alkanes, whereas naphthenic oils have a high share of cyclic alkanes in the mixture.
Heavy oil production is a developing technology for extracting heavy oil in industrial quantities. Estimated reserves of heavy oil are over 6 trillion barrels, three times that of conventional oil and gas.
An oil water separator (OWS) is a piece of equipment used to separate oil and water mixtures into their separate components. There are many different types of oil-water separator. Each has different oil separation capability and are used in different industries. Oil water separators are designed and selected after consideration of oil separation performance parameters and life cycle cost considerations. "Oil" can be taken to mean mineral, vegetable and animal oils, and the many different hydrocarbons.
In an oil and gas production, flash-gas is a spontaneous vapor that is produced from the heating or depressurization of the extracted oil mixture during different phases of production. Flash evaporation, or flashing, is the process of volatile components suddenly vaporizing from their liquid state. This often happens during the transportation of petroleum products through pipelines and into vessels, such as when the stream from a common separation unit flows into an on-site atmospheric storage tank. Vessels that are used to intentionally “flash” a mixture of gas and saturated liquids are aptly named "flash drums." A type of vapor-liquid separator. A venting apparatus is used in these vessels to prevent damage due to increasing pressure, extreme cases of this are referred to as boiling liquid expanding vapor explosion (BLEVE).
Crude oil stabilisation is a partial distillation process that renders crude oil suitable for storage in atmospheric tanks, or of a quality suitable for sales or pipeline transportation. Stabilization is achieved by subjecting ‘live’ crude to temperature and pressure conditions in a fractionation vessel, which drives off light hydrocarbon components to form a ‘dead’ or stabilized crude oil with a lower vapor pressure.
The Teesside oil terminal is a major crude oil reception, processing, storage and export facility at Seal Sands, Middlesbrough. It receives and processes crude oil delivered by the subsea NORPIPE pipeline from the Norwegian Ekofisk field and the UK Fulmar and J-Block fields. The terminal includes facilities for exporting stabilised crude oil and liquefied petroleum gases (LPG) by tanker and pipeline.
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