In this paper, we address the methodology to conduct a comprehensive parametric simulation study of the mechanisms of gas storage aquifers and the analysis of the simulation results. Our simulation results show some effects of the primary reservoir parameters on aquifer gas storage performance not discussed in previous papers by our literature searching, such as the negative effects of formation dip angle on a gas injection/withdrawal process. A homogeneous model of a gas storage aquifer was designed to investigate the effects of the primary reservoir parameters and gas injection and withdrawal schemes on the performance of aquifer gas storage. A heterogeneous model was designed to investigate the significance of the difference of gas storage performance between homogeneous and heterogeneous models. Primary reservoir parameters and their representative values were chosen and designed to reflect the most common reservoir characteristics and well operation conditions. The correlated variations between the investigated parameters and some noninvestigated parameters were considered in our simulation study by using previously published correlations. The effects of gas injection/withdrawal strength, well perforation scheme, and formation heterogeneity on gas storage performance were also investigated, which will be discussed in a separate paper. The correlation relationship of the simulation results at different gas injection/withdrawal strengths and perforation schemes were investigated. Our parametric simulations show that formation permeability is the most important parameter affecting cumulative gas recovery. Formation dip angle and porosity are of second-order importance in affecting cumulative gas recovery. Under the same perforation scheme and gas injection/withdrawal scheme, homogeneous models have much higher cumulative gas recoveries than heterogeneous models, especially in the earlier gas injection/withdrawal cycles. Cumulative gas recovery is mainly dominated by permeability, compressibility, porosity and formation dip angle.
Analyzing or designing a gas storage reservoir requires a thorough understanding of the gas storage performance of the reservoir, which is largely determined by the primary reservoir parameters, such as aquifer size, reservoir structure, and the thickness of a storage zone, as well as rock properties, such as permeability and porosity. Systematically investigating the effects of these parameters on aquifer gas storage performance is very important for achieving the best understanding of aquifer gas storage reservoirs. However, only a few investigators(1)(2)(3)(4)(5) have tried to address the effects ofvarious parameters on the performance of aquifer gas storage reservoirs. None of these have presented a clear and comprehensive study of the factors affecting aquifer storage. In this research, we made a series of parametric simulation runs to comprehensively investigate the basic mechanisms of fluid flow in gas storage aquifers. Unlike most general parametric simulation studies which usually only change the values of the investigated parameters in each simulation case, in our simulation cases, the values of some important related parameters will automatically be changed using published correlations. A two-dimensional (2D), two-phase (2P) crosssectional aquifer model was used in this research to perform the simulation study. The aquifer was modeled by large-gridblocks, which can provide a numerically uniform analysis of the aquifer system.
