The main goal of the COS application is to enable users to run gas cavern simulations based on live measurements acquired from the automation system and to store, analyse, display and export all required results of such simulations. The simulations are performed by the calculation engine provided by ESK GmbH. Cavern Operation Simulator (COS) supports business processes related to simulations of the behavior of gas caverns that must be performed by engineers of the gas storage plant.
Operational Engineers – to support daily calculations for meeting potential gas nominations, hydrate formation restrictions, exportable and importable gas volumes, etc.
The main objective of gas caverns operation simulator (COS) is to provide the gas storage operator with accurate and practical information regarding the actual availability, state and simulated behavior of gas caverns.
The results of each simulation can be stored for analysis, used to compare to each other, exported to files of various formats, displayed and processed.
The calculations are performed with a built-in, proven and reliable algorithm prepared by ESK GmbH (Germany).
First of all COS supports technical processes but also provides the information suited to help commercial business processes.
It allows on-time response to enquiries provided by gas storage market participants, commercial management, portfolio management, gas distributors and other storage users regarding flexible storage utilization.
COS is used to support gas cavern storage operators in their day-to-day business as well as subsurface engineers for planning and design purposes.
The core of COS is the cavern model which comprises all thermodynamic processes associated with gas storage operations in salt caverns such as:
- PVT relationships
- Heat transfer between storage medium and surrounding rocks
- Friction losses due to fluid flows along production tubing and connection pipelines
Parallel to thermodynamic calculations, the implemented rock mechanic option, provides the information about the operationally induced shrinkage of each individual cavern. Whenever individual caverns are operated in a pool, COS manages the distribution of the total flow rate to each cavern via a single nodal point which is commonly represented by a manifold.
Different lengths and diameters of connection pipelines between manifold and individual cavern heads are considered in the model.
The model is mainly running as a prediction tool, but can be used for historical analysis in order to investigate correctness of used model parameters in relation to real cavern behavior. In the prediction mode it is possible to:
- Forecast possible injection/production flows on a given rate schedule (considering individual operational constraints) as well as specified PVT values
- Recognize hydrate formation conditions
- Optimize amount of inhibitor to mitigate hydrate formation
For planning purposes the model is used to find the best configuration of caverns (spatial volumes & depths) and necessary numbers of single caverns to fulfil the required volume and rate capacity.
Possible user roles in the COS
- Sub-Surface Engineers - users responsible for the modeling of caverns and having access to all functionalities of the application.
- Operational Engineers - users responsible for the daily usage of COS, running scenarios, viewing and exporting reports. These users have usually restricted access to caverns modeling functionality of Cavern Operation Simulator.
- Maintenance Engineers - users responsible for planning and measures of maintenance.
- Management - users responsible for Strategic Planning or informative use.
Cavern Operation Simulator advantages
- Automated acquisition of measurements data from external source systems
- Management of multiple models, measurements, simulation inputs and results
- Short and long term analysis of the storage behavior (e.g. prediction of pressures and temperatures for all caverns)
- Possibility to calculate the production and injection gas volume for any time horizon up to 1 year
- Tools for data analysis, charts, tabular views
- Import and export simulation results from/to external files for further analyses
- Support of business processes of storage plant operators
- Verification of commercial nominations
- What-if analysis at the level of the storage design and construction.
Integration with automation systems
Cavern Operation Simulator (COS) software is integrated with the Enterprise Data Server (EDS) provided by Transition Technologies S.A. as an integral part of the system.
EDS software is used for data acquisition from automation systems and for data processing. It allows supervision of technological processes based on recorded measurements and calculated indexes. The system enables continuous monitoring of all technical processes.
The main functionalities include:
- Integration of process data from various systems (e.g. PCS7)
- Aggregation of data prior to their use in other software components
- On-line measurements validation
- Analysis of technical and process data
- Complete visualization of production processes at all levels
- Events and alarms processing
- Unified time stamps for data from various sources.
The EDS part of the system, which is responsible for overtaking and processing real-time measurements for COS application is generally installed on two redundant servers providing the high availability of the system to ensure the continuous update of the caverns pool model.
Measurements collected from the automation system
COS uses the following information for precise modeling:
- Date/Time (full hours) - associated data is assumed for the time step ending at this time
- Gas flow rates (injection/withdrawal) volume or energy based
- Cavern availability information [for each individual cavern]
- Gas injection temperature (at each individual wellhead)
- Composition of injected gas for following components: CH4, C2H6, C3H8, n-C4H10, i-C4H10, C5+, N2, CO2
Using optional data like head temperatures [°C] for each individual cavern, head pressures [bar] for each individual cavern, single flow rates for each individual cavern [Mio.Sm3/day or Nm3/h] is possible to exactly determine the quality of the model results.
The integration allows the management of cavern pool models, running simulations, configuring input data and browsing the results. Cavern Operation Simulator can be started in the prediction mode or in the state update mode, so the model of the caverns can be used for analyses of a current cavern pool state or for analyses of future gas site state. COS also gives wide possibilities to monitor the process data, their quality and the quality of connections between the systems responsible for process data flow.
COS is designed to handle data series of any time granularity (for example minute, hour, day, any other). It provides the functionality to view this data in a tabular form and on charts (bars, trends). Additionally any time series can be exported to the CSV file.
Simulation and evaluation of results
The simulation engine which is invoked by COS application in the background is the most important part of the COS solution.
For each time step COS reads one record of data, which is generated using the above mentioned information. For these purposes COS can generate corresponding reports (measurements vs. model results).
The COS application is also able to export the most actual model state (for manual adjustment) and to import it again into COS database to check the results of the modification with real time measurements.
At the end of each time step, COS generates a record containing calculation results. One part of the results is common for the whole pool of caverns, another part (most of the values) presents individual parameters for each single cavern.
As a results of simulation COS displays more than 50 parameters for cavern pool and for every cavern separately. Example of results are listed below:
- Total gas volume
- Wellhead, cavern & casing shoe pressure
- Manifold pressure
- Pressure fall off/build up rate at LCCS
- Cavern & wellhead temperatures
- Available stock/space
- Gas flow velocities at wellhead
- Cavern convergence and corresponding spatial cavern volume
- Surface subsidence
This information helps operators to better understand the behavior of the storage and take optimal decisions concerning gas storage operations.
Cavern Operation Simulator client
COS client works as a web application accessible via web browser but it can be also installed on the computer in out of browser mode as well. That depends on decision of COS user.
COS users are also authorized and their activities are logged and reported. The system keeps audit trail of all activities performed by the application.
Access to the system is restricted to those users with appropriate privileges (could be integrated with enterprise Active Directory accounts).