Design method of key parameters of gas reservoir engineering for complex reservoir type underground gas storages

The underground gas storages (hereinafter referred to as UGSs) rebuilt from oil and gas reservoirs in China are characterized by great burial depth, complex structures, poor reservoir physical properties, and strong heterogeneity. The UGS construction targets in China involve complex types, such as complex fault blocks, strong water invasion, abnormal pressure, and high oil content condensate gas reservoir, so conventional gas reservoir engineering parameter design methods are not applicable, and especially there are some special requirements for trap sealing analysis, storage capacity parameter design, and injection–production capacity evaluation. Focusing on these difficulties, this paper carries out independent innovation and technological bottleneck breakthrough. Beginning with the geological characteristics of UGS construction targets, the four-dimensional dynamic sealing evaluation technology for complex fault block UGSs is developed, and the storage capacity prediction method for abnormal pressure UGSs and the zonal multi-factor coupled injection and production capacity prediction model for water invasion UGSs are established. In addition, the new condensate gas-reservoir UGS construction model of "Enhanced Oil Recovery (EOR)–collaboration–gas storage" and the optimized technical strategies are demonstrated. And the following research results are obtained. First, physical simulation experiments reveal the fatigue damage and fault slip mechanisms in the cap rocks of complex fault block UGSs, so as to enable the quantitative evaluation of dynamic sealing indicators, which lays an importation foundation for the site selection of complex fault block UGSs. Second, in view that the rocks of ultra-high-pressure fractured UGSs exhibit strong stress sensitivity, a new effective storage capacity prediction method considering compressibility coefficient change and bound water expansion is established, and a multi-cycle injection and production capacity prediction method considering cycle time change and water invasion is formed for different zones of strong water invasion UGSs, so as to achieve a scientific design of UGS construction parameters. Third, a new model of condensate gas reservoir EOR collaborated with UGS construction is established, the rational transition timing of "EOR–collaboration–gas storage" is determined, and the staged UGS construction parameter design method and the well pattern deployment strategies are prepared. In conclusion, the proposed design method of key parameters in gas reservoir engineering of complex oil- and gas-reservoir UGSs provides a powerful support for Sinopec's construction and operation of complex oil- and gas-reservoir UGSs, and has a good guiding role in the construction of similar UGSs. © 2023 Natural Gas Industry Journal Agency. All rights reserved.