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The tank material balance method is often
quite adequate for analysing gas reservoirs. In such cases,
it is possible to treat the reservoir as a huge "tank" of
constant volume, for which a plot of P/Z versus cumulative
gas produced (Gp) is a straight line intersecting the axes
at the initial pressure and GIIP respectively. This allows
accurate predictions, for example average reservoir
pressure, to be made.
Unfortunately, there are a number of reservoir features
which will cause the P/Z plot to depart from a straight
line, for example aquifer influx or gas influx from
un-represented sources such as poor quality rock or unmapped
gas pockets. However, it is possible to take such features
into account by making modifications to the basic material
balance equation. Hence, when modelling complex gas
reservoirs, GASMAN uses a modified material balance
approach. This approach takes into consideration aquifer
influx, multi-tank gas transmissibility and condensate/water
production.
In practice, producing gas fields often consist of a number
of isolated reservoirs with different characteristics.
Moreover, each reservoir will be linked to a pipeline
network through a number of wells connected at the surface
through gathering centres. This network takes the gas to a
central processing facility. To model such complex systems,
MSE has extended the basic gas material balance method to a
multi-tank, multi-well configuration. |
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