Reservoir Simulation by Material Balance

In GASMAN, gas and gas-condensate reservoirs are represented by the material balance method. Multi-tank modeling allows representation of more complex reserves. Each reservoir tank can be connected to up to four others via gas transmission factors, allowing material influx or efflux. Where required, pressure support can be provided by aquifer modeling via single or multi aquifer tanks with individual water transmission factors.

Material balance is modeled through time covering gas and condensate production from each well (or injection in the case of gas storage) and influx and/or efflux to/from neighboring reservoir tanks. By running GASMAN in batch mode (in time steps of days or months) the production profiles for each reservoir tank are calculated based upon the solution derived from the integrated model. This integrated approach can have particular relevance when there are strong interactions between topsides equipment and the well network and gathering system. The resulting production (or injection) profiles may be limited by, for example, compression system capacity rather than well capability.

Where required "uptime factors" can be applied to the rate of depletion or injection - making allowance for planned shutdowns or maintenance intervention.
Reservoir fluid properties may be represented by either a fully compositional (equation of state) approach or by the black oil method.

The validation of reservoir performance in GASMAN is carried out using a combination of history matching techniques and alignment of GASMAN forecasts against leading industry software models used by our clients.

In reservoir simulation technology, forecasting the performance of gas storage fields is probably one of the most difficult tasks. This is because the changes in pressures experienced by storage reservoirs during a one year period correspond to the entire life of the gas field. This is because the reservoirs are filled with gas during summer months, and evacuated during winter months, therefore, the reservoir model has to be extremely accurate in order to model a gas storage facility.