Definition – What does Stock-Tank Oil Originally In Place (STOIIP) mean?

Stock-Tank Oil Initially In Place (STOIIP) is the total amount of crude oil present in a hydrocarbon tank before production begins. Since it is not possible to measure the total volume or the exact amount of oil in the hydrocarbon reservoir, other parameters consider and examined to evaluate the oil estimate. It is similarly known as Oil in Place (OIP) and Stock Tank Original Oil in Place (STOOIP).

Storage Tanks

A storage tank is designed to hold the oil produced and separated until it is sold. Its arrangement is quite similar to the barrel of a cannon, and the water will continue to fall from the oil until it carry through a pipe or truck. Therefore, a system is required to remove the sewage, even with storage tanks. Classically, you need to accumulate enough oil to fill a 210-barrel shipping tank. You don’t need the entire 210 barrels, more like 160 to 180. More than that, and a truck is too heavy for most roads and highways.

A standard tank differs, among other things, in that the level of liquid inside must measure frequently. A standard method is to use a simple plumb line and string. However, dropping a metal plumb bob to the bottom of the tank several times a day can eventually damage the tank.

Petropedia Declares Stock-Tank Oil Initially In Place (STOIIP)

Storage tank oil initially in place is the volume of oil available in a hydrocarbon tank before production begins in the same amount that the oil will absorb if stored in a storage tank. Mathematically, STOIIP can express as:

  • STOIIP = BV x F x (1-Swi) / Bo,
  • Where,
  • BV = storage volume of the reservoir
  • F = effective porosity of the oil rock
  • Swi = initial water saturation
  • Bo = volume correction factors

Volumetric methods estimate the current oil level or the initial amount of oil in a reservoir. An estimate of the size of the oily rock made by performing a series of test wells in nearby locations and, based on the results, the conditions of the stone map.

A New Method For Stock-Tank Oil Compositional Analysis.

A new method develop and validated to accurately determine reservoir oil composition in normal pentatriacontane by gas chromatography. The new way solves possible errors associated with traditional equipment and technique used for extended hydrocarbon gas chromatography outside of a controlled laboratory environment, such as on an offshore oil platform. In particular, the experimental measurement of the molecular weight of the oil from the reservoir. With the technique of lowering the freezing point. And the use of an internal standard to find the fraction of the sample not recovered replace by correlations to estimate these properties. The use of correlations reduces the number of experimental steps required to complete the necessary sample preparation and analysis, reducing the uncertainty of the research.

Also Read: The Function and Operation of the Duplex Strainer and Duplex Filters

When Can A Stock-Tank Oil Be A Condensate?


Database plots of the distribution of C7+ to C40+ fractions and fraction density and molecular weight show a clear statistical difference – with a minor overlap. Between stabilized hydrocarbon liquids from reservoir gas (condensate) and reservoir oil. In most cases, the origin of a stock-tank oil sample can interpret based on composition, density, molecular weight, and reservoir pressure.

Typically, hydrocarbon liquid with density higher than 0.85 g/cm3 and also C7+ molecular weight > 250 g/mol origins from reservoir oil, during hydrocarbon liquid with density lower than 0.8 g/cm3 and C7+ molecular weight < 170 g/mol origins from reservoir gas.

The primary drive of the present paper is to identify cases where composition. Molecular weight, and density show that a hydrocarbon liquid sample cannot originate from a reservoir gas at given reservoir pressure. In addition to statistics from an extensive PVT database, provided that additional proof for such cases.

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