Abstract
This paper presents analysis of the performance of Chiren Underground Gas Storage Field located in Northwest Bulgaria. The storage was built in a depleted gas condensate reservoir. The producing formation comprises of fractured multi layered carbonate and sandstone rocks. The gas field/storage has been object of several controversial studies.
The paper includes analysis of the influence of rock deformations, water drive, and effect of the capillary processes, from the period of gas field to the recent days. In the study, data from the 30 years history period, laboratory data as well as mathematical simulation are used.
The results show significant influence of the heterogeneity of the formation, production injection schedule, and the well spacing. Progressive time dependent gas dis-balance is observed. Evaluation shows that it is in the range of 1/3 the peresent stored gas volume in the reservoir. Well logs prevail good state of the production casing and luck of gas migration in upper formations. Simulation shows that the main reasons for the gas dis-balance and formation of zones with higher pressure as a result of water movements, formation rock deformation and well water cut. The inadequate reservoir management has neglected those factors and it seems it's the main reason for the bad reservoir performance.
