Laboratory simulation experiment of well-leak monitoring of salt-cavern gas storage

The injection/production well of salt-cavern underground gas storage tends to suffer leak due to long-term influence of alternate temperature and stress on pipe string and set cement. In order to ensure the smooth and safe operation of salt-cavern underground gas storages, laboratory simulation experiment of well-leak monitoring was carried out based on optical-fiber distributed acoustic sensing system (DAS). In the experiment, the tubing-casing string combination of Ø177.8 mm and Ø244.5 mm was selected to simulate a salt-cavern underground gas storage, gas was injected into the internal pipe, liquid was injected into the annulus, the middle thread was set as the leak point, and the internal-external pressure difference was controlled in the range of 0-12 MPa by virtue of nitrogen injection. The simulation was conducted by means of DAS and noise logging technology. It is determined that the leak characteristics of the distributed vibration fiber based leak monitoring system are abnormal shows on DAS waterfall plot and DAS spectrum map. Its accuracy is within ±1 m and lower limit of leak measurement is 0.83 L/min. This system can perform effective discrimination and real-time monitoring of gas leak in the process of injection and production and provide the technical support for developing a kind of technology suitable for monitoring the well-leak of salt-cavern underground gas storage.