Estimates of Compressibility of the Pore Space of the Reservoirs of the Uvyazovskoe Underground Storage Facility

The results of experimental studies of the effect of alternating changes in reservoir pressure on the volumetric compressibility of gas storage reservoirs have been reviewed. Several approaches to estimating volumetric compressibility are considered: integral, differential–additive and differential–discrete, which differ in their choice of the interval of effective pressure changes. It is shown that different approaches give different estimates of the volumetric compressibility of the pore space. It is established that the application of the differential–discrete approach allows the most adequate estimation of the pore compressibility during gas injection and circulation. Specific petrophysical parameters of the gas storage reservoir have been considered and, on their basis, estimates of the coefficient of volumetric compressibility of the pore space have been obtained. A methodology has been developed and tested in practice to estimate changes in vertical surface displacements of an underground gas storage facility, which takes into account actual changes in the porosity and compressibility of gas reservoirs depending on the selected operating mode. Using the developed mathematical models, we have estimated the maximum amplitude of surface subsidence of the Uvyazovskoe underground gas storage facility during simulation of gas injection and withdrawal, which reaches 61 mm when the reservoir pressure changes by ±5.0 MPa.