Multiphase Modelling of a Gas Storage in Aquifer with Automatic Calibration and Confidence Limits
Résumé
Multiphase flow modelling involving gas and water is widely used in gas dissolution in aquifers or in aquifer gas storage. The parameters related to the gas are usually well known but the parameters of the aquifer system are not. In order to obtain reliable forecasts, it is necessary to calibrate the multiphase model on monitored data. This can be done by automatic calibration followed by the determination of the confidence limits of the parameters, and of the confidence limits of the forecasts. This paper presents a three-dimensional multiphase flow model for the simulation of gas-water, or NAPL-water couples. It integrates automatic calibration procedures based on Marquardt's algorithm for all types of parameters: hydraulic conductivity, which is classical, and also multiphase flow constitutive relations, aquifer compressibility and boundary limits. The model may be calibrated simultaneously on observations of different kinds of data, e.g. gas pressure, hydraulic heads, water saturation. A sensitivity analysis method, which integrates spatial or temporal dependence of the observations, follows the automatic calibration. The model is applied to data from a gas storage facility located in a gas cap in an aquifer near Paris (France); it has been monitored by the national Gaz de France company for more than 30 years. The automatic calibration enabled determination of the hydraulic conductivity, the rock compressibility and the lateral boundary limits. It resulted in a very accurate simulation of the gas pressure changes resulting from the periodic injections and withdrawals of gas. The sensitivity analysis enabled determination of the parameters that were the most important.
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