Experimental simulation on the fine migration induced by the violent change of the gas injection pressure of gas storage well

Fine migration is one important type of reservoir damage. Fine migration in reservoirs is induced by the progressive increase or fluctuation of gas injection pressure during the gas injection of underground gas storage well. So far, the mechanisms of fine migration induced by the change of the gas injection pressure of underground gas storage have not been clarified clearly and the experimental study on the fine migration due to the change of gas injection pressure has seldom been carried out systematically. The cores of the Huanglong Formation carbonate reservoir in Xiangguosi Underground Gas Storage were selected to prepare fractured cores. They were used to carry out stress sensitivity experiment, gas velocity sensitivity experiment, core flow experiment under the simulated progressive increase and fluctuation situations of gas injection pressure of underground gas storage and test the core permeability and outlet fine turbidity under the influence of progressive pressure increase and pressure fluctuation. And by means of X-ray diffraction and scanning electron microscope (SEM), the potential types of fine migrating in reservoirs were analyzed and the migration mechanisms of fine induced by the dynamic change of the gas injection pressure of underground gas storage were revealed. The experiment results show that the pressure gradient in the experiment with progressive displacement pressure increase and pressure fluctuation is much higher than the critical pressure gradient corresponding to the occurrence of velocity sensitivity (fine migration) in the velocity sensitivity experiment, indicating that the core’s stress sensitivity degree is weak and moderate-weak. In addition, the average damage rate of core permeability under the influence of progressive displacement pressure increase and pressure fluctuation is 77% and 57%, respectively. What’s more, the decrease of the adhesive capacity of the vulnerable structure on the wall surface of reservoir fracture caused by progressive displacement pressure increase and pressure fluctuation is the important mechanism inducing fine migration. In conclusion, progressive gas injection pressure increase or frequent pressure fluctuation can induce fine migration to damage the reservoir of underground gas storage, so it is recommended to prevent the invasion of foreign solid fine in the process of drilling and completion and remove the autochthonous fine in reservoirs.