Average Areal average reservoir pressure around a well. around a given reservoir location
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The definition of "areal average" is quite straightforward for wells which have never been produced and simply means the reservoir pressure at the well-reservoir contact.
In producing/injecting wells or wells which have been shut-in after production/injection the definition of "areal average" is ambiguous and defined The averaging procedure is defined in several ways depending on applications and summarized as summarised in the table below:
Formation Pressure Defintion | Application | |||||||||||||||||||||||
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Shut-in formation pressure estimate based on a wellbore sandface pressure after a given well is shut-in for
| This definition is based on the practical observation of wellbore pressure in shut-in wells for well intervention purposes. It is the simplest and the most popular definition of formation pressure and is widely used in all upstream industry applications. The definition of shut-in time
Some conventions are to pick
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along the boundary of drainage area
where
| This definition is based on the idea that there is a boundary line
The advantage of this method over
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formation pressure estimate within the drainage area
| Well Flow Performance Analysis This definition is based on the productivity index estimate and assumption that it stays constant Historically this definition is |
using a |
specific symbol
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9-cell formation pressure estimate from reservoir flow simulation model
| It defines formation pressure as an arithmetic average of |
reservoir pressure values in |
all cells of reservoir flow simulation model adjacent to the cells containing a well-reservoir contact. In a particular case of vertical well the adjacent cells will be 9 cells around a cell with vertical well which raised the term 9-cell formation pressure. It provides a very rough and often inaccurate estimate of formation pressure |
and often used in history matching. It should be used with caution when planning new wells, workovers, well performance analysis and testing existing dynamic model against other estimates. |
A more accurate model estimate of formation pressure can be retrieved from a proper well shut-in in reservoir flow simulation model. |
See Also
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petroleum Geology / Reservoir pressure
Subsurface E&P Disciplines / Production Technology
[Reservoir pressure] [Initial formation pressure, Pi] [Drilled formation pressure, Pd] [Startup formation pressure, P0] [ Multiphase formation pressure ]