PORTEC is a material balance model developed in-house by ESK to simulate gas storage processes in porous rock formations (depleted or partly depleted hydrocarbon reservoirs, aquifer structures). The software tool supports storage operators in their day-to-day business and assists subsurface engineers in planning and designing storage facilities. PORTEC consists of three linked modules ­ (reservoir, wellbore and above-ground facility), representing all relevant hydrodynamic and thermodynamic processes during injection, withdrawal and shut-in periods from the manifold to the reservoir and vice versa.

The model covers all processes associated with gas storage operations in porous rock formations such as:

Reservoir module

• Pressure-volume relationships in the storage formation resulting from withdrawal/injection of gas
• Pressure changes in the storage layer due to aquifer influx
• Hydrodynamic communication between adjacent reservoir compartments

Well module

• Inflow performance (IPR)
• Vertical flow performance (VFP)
• Water cut versus production volumes and rates

Above-ground facility module

• Pressure losses along interconnecting lines between individual wellheads and a common manifold
• Input data such as reservoir parameters, well data, gas compositions etc. can be edited via an easy-to-use pre-processor (ParEdit). Instead of a detailed finalisation plan, single wells can also be characterised by means of appropriate performance figures generally interpreted from well test data.
• All calculation results can be displayed in table and chart view.

The model can be run as a forecasting tool or can be used for back analyses, i.e. investigation the actual reservoir and well behaviour by applying common history match procedures. The history match procedure allows initially selected parameters to be adjusted to real storage behaviour, qualifying the model as a reliable prediction tool.