Increasing Working Gas Volume of UGS Based on Low Permeability Lithological Gas Reservoirs

A low-permeability lithological reservoir was successfully put into operation in 2015 as a gas storage system. The field S2 Underground Gas Storage (UGS) is located in the Ordos Basin and is primarily alithological trap, with low permeability, high heterogeneity, and no obvious seal boundaries. Based on low permeability, low abundance, low vertical wells productivity, low pressure coefficient, serious skin damage in the bottomhole during drilling and completion, strong heterogeneity and unclear lithological boundaries, low control of injection-withdrawal well patterns, the working gas volume and operating efficiency of S2 UGS underperformed relative to modeled expectations. The technical solutions to improve the working gas volume of S2 USG focused upon: well pattern optimization, well placement, stimulation treatment, infillings, and increasing of operating maximum pressure. The results demonstrate that if reasonable technical solutions are adopted, even poor and low-quality storage reservoirs with low permeability, and strong heterogeneity, can be utilized as natural gas storage targets. This discussion provides an overview of approaches used in the Ordos Basin to make operation of S2 UGS more efficient. The development of this project, particularly regarding the operation processes and the resulting adjustments, are noteworthy. The development of such UGS reservoirs require new insights into the performance criteria which can be applied to other reservoirs in the future.