Oil in place (OIP) (not to be confused with original oil-in-place (OOIP)) is a specialist term in
petroleum geology
Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons ( oil exploration).
Sedim ...
that refers to the total
oil content of an
oil reservoir
A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.
Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presenc ...
. As this quantity cannot be measured directly, it has to be estimated from other parameters measured prior to
drilling
Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...
or after production has begun.
Prior to
oil production from a new reservoir, ''volumetric'' methods are used to estimate oil-in-place. A series of
test drills
Test(s), testing, or TEST may refer to:
* Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities
Arts and entertainment
* ''Test'' (2013 film), an American film
* ''Test'' (2014 film), ...
are used to map the rock conditions at and around the drilling site and to estimate the size of the oil-bearing rock field. The oil in place is calculated as the product of the volume of porous oil-bearing rock, the
porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
of the rock, and its saturation.
Correction factors have to be applied for the difference between the volume of the same mass of oil in the reservoir to its volume when brought to the surface, which is caused by the different physical conditions (temperature, pressure) there.
Oil-in-place is also known as stock tank original oil-in-place (STOOIP) or stock tank oil-initially-in-place (STOIIP), referring to the oil in place before the commencement of production. In this case, ''stock tank barrels'' refers to the volume of oil after production, at surface pressure and temperature (as opposed to reservoir conditions).
After production has begun, the change in reservoir pressure over time and the history of production from that reservoir can be used to estimate the total oil-in-place using the ''
materials balance'' method. Alternatively, the production history can be fitted to a curve to estimate future oil production (''decline curve method'').
The analogous term original gas-in-place (OGIP) is used to refer to the total
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...
in a reservoir. Furthermore, there is a term called Hydrocarbons Initially in Place (HCIIP) that is used for either oil or gas. Similar to OIP, HCIIP is calculated using measures of the total reservoirs volume correcting for the non reservoir rock, the porosity and the water saturation in this pore space. Lastly the volume at reservoir conditions (high pressures and temperatures) is converted to the associated volume at surface conditions.
Oil in place must not be confused with
oil reserves
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
, that are the technically and economically recoverable portion of oil volume in the reservoir. Current recovery factors for oil fields around the world typically range between 10 and 60 percent; some are over 80 percent. The wide variance is due largely to the diversity of fluid and reservoir characteristics for different deposits.
See also
*
Stock Tank Oil
References
{{reflist
External links
Reserves estimation at AAPG Wiki. Includes four methods to determine OOIP and OGIP.
Petroleum production