Optimized Gas Injection Rate for Underground Gas Storage; Sensitivity Analysis of Reservoir and Well Properties

摘要

Increasing demand for natural gas during cold months has forced gas companies to store excess gas into the porous rock formations in summer. This artificial reserves known as underground gas storage (UGS) brings more flexibility to the natural gas provider companies to have enough gas available for peak customer demand. An important parameter that controls the feasibility of any UGS project is the time needed to inject the gas for the storage preparation. This would clearly affect the withdrawal-injection cycles for different gas injection rates which requires an optimum injection rate based on the rock and storage properties especially the maximum pressure for the cap rock stability. The purpose of this work is to examine a case study to find the optimum injection rate, i.e., the rate by which as much gas as possible is injected into the field with the highest bottom-hole pressure that is secure. Moreover, this optimum injection rate must be constant during the preparation's period. Optimum injection rate is a function of reservoir properties like vertical/horizontal permeability ratio (k_v/kh), skin factor, horizontal permeability and the well perforation's locations. Sensitivity analysis was performed using fluid flow simulation technique. The results show that horizontal permeability is the most dominant parameter on the amount of optimum injection rate, while the amount of k_v/kh has the least effect. The perforation's locations has a linear relationship in a way that the summation of optimum injection rates measured for each perforated layer is approximately equal to the optimum injection rate found for fully perforated case. Skin factor was found to be the intermediate pertinent parameter; however when skin factor is in negative ranges, it leads to higher injection rate. The results show that only one well with negative skin can inject as much gas as several wells that reduces costs of drilling for new wells.