GASMAN - Operation

GASMAN is a complete model of a gas production system from the reservoir to export pipeline discharge, and is therefore used to analyse the performance of a system as a whole.

The effects of reservoir depletion, well fouling, changing ambient conditions, degradation of compressor performance, etc, on the whole system can be determined for any given operating scenario.

The program can be run in either interactive mode or batch mode. In interactive mode, key parameters can be selected such as flows, temperatures and component degradations which the GASMAN system then uses to evaluate system performance. In batch mode, changes in parameters can be specified over a period of time and GASMAN then analyses the system's performance throughout that period.

Interactive (Single Step) Runs

Interactive runs are used for production forecasting and optimisation. Either flow or pressure at the platform inlet can be specified together with platform discharge pressure.
GASMAN is then used for production forecasting, or to determine the equipment's design limits. It also optimises gas production. This is determined by adjusting flows to the maximum possible value and discharge pressures such that none of the key items of equipment (i.e. gas turbines/compressors) operate beyond their design limits.

Mode - Time Stepping

GASMAN simulates the actual operation of a gas field using time stepping. It can be operated at specified time intervals to determine the reservoir and surface facilities over a given time period. The software determines production rates and adjusts gas "in place" and dynamically adjusts the reservoir pressure, well performance, etc. This facility enables the examination of the impact of reservoir pressure decline on compressor performance to be carried out in real time.
This mode is selected to examine the impact of changing certain parameters (e.g. a set of contract flow nominations) over a period of time on the performance of the entire production system.

In a batch run, the following parameters may be altered at each time interval:
 

	Compression platform inlet flow
	Number of wells producing
	Well fouling
	Compressor fouling
	Compressor efficiency degradation
	Flow by output (contract nomination)
	Ambient pressure
	Ambient air temperature
	Ambient sea temperature

In addition, the effect of production on the depletion of the wells may be reviewed.
Reservoir depletion is calculated and new IPR curves are generated automatically based on the gas produced from the tank; hence the flow and pressure of each contributing well is determined. Arrival pressure at the platform and at compressor inlet is established.

Compressor and gas turbine performance are determined. The effect of varying ambient conditions can be analysed with the batch facility.

GASMAN's batch mode time stepping facility is the most powerful one available for production forecasting.

Solvers

This functionality enables the integrated GASMAN model to be run to a specific user-defined rule by adjusting other variable/s until this rule is achieved or is close to being achieved.

For example, the model might be set to "always run to the maximum turbine power for all conditions except when limited by the performance of other modules".
Solvers may be used in interactive runs or batch runs and are quite useful when carrying out production or maximum deliverability forecasting.