Areal average reservoir pressure around around a given reservoir location.
The definition of "areal average" is quite straightforward for wells which have never been produced or have been shut-in for a long time and simply means the pressure at the well-reservoir contact.
In producing/injecting wells the definition of "areal average" is ambiguous and defined averaging procedure is defined in several ways depending on applications and as summarised in the table below:
Formation Pressure Defintion | Application | |||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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
| |||||||||||||||||||||||||||||||
Boundary-average formation pressure estimate 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
| |||||||||||||||||||||||||||||||
Field-average 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 marked with a different symbol
| |||||||||||||||||||||||||||||||
9-cell formation pressure estimate from reservoir flow simulation model
| It defines formation pressure as an average of numerically calculated pressure values in 9 grid cells of reservoir flow simulation model It provides a very rough and often inaccurate estimate of formation pressure for planning new wells, workovers, well performance analysis and testing existing dynamic model against other estimates. It is widely used in history matching as input parameter to match with, which maybe highly controversal providing the difference in. |
See also
...
Initial formation pressure, Pi
Startup formation pressure