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Features of ﬂuid dynamics in long-term heterogeneous gas reservoirs

Geological features are characterized by macro- and micro-heterogeneity, manifested by the spatial variability of material composition and lithophysical properties of rocks. This, in turn, determines the spatial and temporal variability of hydrocarbon (HC) ﬂuid dynamics both during the reservoir formation and during its development and, subsequent operation as an underground gas storage facility (UGSF). The long-term operation of underground gas reservoirs at the Galmas and Garadagh areas in the South Caspian Basin (SCB), serving as a reservoir of commercial gas accumulations, and subsequent underground gas storage (UGSF) is characterized by signiﬁcant peculiarities. Analysis of monitoring data on volumes of gas injection and extraction at the Galmas/Garadagh UGSF in the period of 2020–2021 showed their spatial variability, as well as the variability of wells deliverability during the gas reservoir development. This suggests the inherited nature of UGSF operation mode in relation to the gas reservoir development mode. The heterogeneous nature of spatial variability of these parameters is determined by the reservoir rock poroperm properties. A formation pressure drop during reservoir development is accompanied by decreasing rock permeability. When operating UGSF, the lithofacial properties of rocks determine the ratio of volumes of injected and extracted gas. In this regard, a necessary condition for selecting the optimal system of UGSF operation is to take into account the spatial heterogeneity of the underground reservoir. The irregular nature of variation of rock poroperm properties, the origination of isolated zones in the reservoir with considerable residual gas volumes, as well as unpredictable directions of ﬂuid movement are the main reasons for decreased efﬁciency of ﬁeld development and underground gas storage facility operation. In order to determine the optimal system of operation of UGSF in depleted underground oil and gas reservoirs, the features of the spacial variations resulting from the rocks poroperm properties need to be taken into account.