Abstract: Depleted and water-flooded oil and gas reservoirs constitute the primary construction carriers of underground gas storage (UGS) facilities in China. Such gas storages are universally plagued by engineering challenges including massive residual formation water volume, severe interlayer reservoir heterogeneity, and reservoir pore clogging induced by long-term cyclic injection-production operations, which restrict the utilization efficiency of gas storage capacity as well as the capacity for rapid commissioning and stable production. Based on an analysis of technical difficulties associated with liquid drainage in the offshore shallow blocks of Jidong Oilfield in the Bohai Bay Basin, this paper proposes an efficient gas-lift liquid drainage engineering technology for UGS converted from oil and gas reservoirs. A two-stage hermetically sealed zonal injection-production gas-lift drainage process and a series of high-flow-rate liquid drainage processes for old wells are designed, with matching downhole tools developed accordingly. Large-scale field application of this technology at Nanpu N Gas Storage has yielded remarkable results: cumulative formation liquid drainage reached 68.70×10⁴ t, effective utilization of the remaining enclosed gas space, increases the effective storage capacity. The research outcomes provide an engineering reference for the renovation of UGS converted from complex water-flooded old oil and gas reservoirs in the Bohai Bay Basin, and also offer critical technical references and practical experience for liquid drainage, pressure reduction, precise capacity expansion and rapid commissioning of similar depleted water-invaded oil and gas reservoirs nationwide.

Key words: gas storage, liquid drainage and capacity expansion, zonal injection and production, injection-production engineering, gas lift drainage