EXPERIMENTAL INVESTIGATION OF WATER VAPORIZATION AND ITS INDUCED FORMATION DAMAGE ASSOCIATED WITH UNDERGROUND GAS STORAGE

Abstract

Water vaporization and its induced damage around the wellbore are important issues with a wide application. This phenomenon may be observed wherever dry gas is injected into gas and oil reservoirs in the presence of connate water. Gas injection for enhanced oil recovery (EOR), pressure maintenance or storage purposes and carbon dioxide sequestrations in aquifers are examples where it could happen. There are two counteracting factors existing in vaporization phenomenon; water saturation decrease and induced permeability impairment by salt precipitation in the porous medium. Water saturation decrease tends to raise injectivity or productivity by providing a higher share of passage to the gas. Salt precipitation tends to reduce injectivity or productivity due to the damages induced. The interaction of these two factors determines how productivity or injectivity will alter. It is a very new subject finding its interest in application; however limited research has been done on this up to now and many aspects are still unknown. We conducted an experiment to investigate the impact of water vaporization on injectivity for core samples of an Iranian sandstone gas reservoir candidate for gas storage. The injection gas used for the drying-out process is taken from a refinery nearby the reservoir to be injected and stored. It is a refined gas (mainly methane) for people's daily use. The experiment is conducted at atmospheric conditions; however the reservoir itself is at high temperature and pressure. The different thermodynamic conditions applied here only change the maximum amount of water that the gas can carry and will have no impact on the process behavior and damages induced since they are controlled by precipitated salts and decrease in water saturation According to the results, the medium with higher permeability experiences an improved injectivity during gas injection while the medium with lower permeability experiences an impaired injectivity. Then the distribution of each medium around the wellbore dictates if a field application would face injectivity increase or decrease. Finally, the interaction of the two effective factors mentioned above differs for each porous medium and water system. Therefore, an experimental investigation for each system should be performed in absence of a general formulation for injectivity or productivity alteration because of water vaporization around the wellbore.