Gas storage in partially depleted gas reservoir

In this paper, we shall present the underground gas storage Okoli, which was selected among several gas fields in the SFR of Yugoslavia. The first part gives a detailed description of the Okoli gas field ''a'' series properties, such as geological-petrophysical characteristics, hydrodynamical reservoir properties, productivity-injectivity well characteristics, production history, etc. By simulation of the reservoir, it was established that drive mechanisms were volumetric, with slight water drive influence. The second part deals with methods of designing and calculating the basic underground gas storage parameters, such as the number and spacing of wells, initial pressure range and the range of pressures as a function of time, number of observation wells, production-injection prediction and the like. Procedures of well testing were developed and a review of successful well stimulation jobs presented. The paper also deals with the injection and production technology. The last part presents results obtained during the first cycle of gas injection, as well as the earliest results of the first phase during the first cycle of gas production from the underground storage. The obtained results confirm the proper choice of the underground storage and the maximum planned production rate was achieved in the first cycle of operation. (author). 6 refs, 5 figs, 3 tabs