Abstract

Based on European Union (EU) Directive 2003/55/EC and Hungarian energy regulator "Magyar Energia Hivatal" requirements, Hungary must have sufficient gas reserves to satisfy a full month's household demand. Although five commercial underground gas storage (UGS) fields were operating in Hungary by 2007, a higher rate of gas production was needed. For this reason, the Hungarian government decided to develop a new UGS field rather than to increase the capacity of the existing ones.

Because of favorable reservoir characteristics, Szoreg field was selected, and 44 wells were scheduled to be drilled in 1½ years. Tight drilling and completion schedules, the operating company's turnkey contract terms, and a fixed budget made critical the success of primary cementing jobs with fit-to-purpose systems and without the occurrence of any type of remedial work.

The drilling plan included 34 vertical or deviated wells and 10 horizontal wells, each with 3 casing strings and gravel-packed completions, with the cementing objectives to provide a top of cement to surface for every casing string. For the last cemented (reservoir) casing, the presence of two sands with a marked difference in formation pressure and separated by a shale cap of only 4 m to 7 m in length required perfect zonal isolation..

Depleted and unconsolidated formations required the use of lightweight slurries to reduce hydrostatic pressure on the formation. For further losses prevention and minimization of formation damage deep in the reservoir, engineered fiber material (EFM) was programmed in the cement slurry based on drilling events.

Furthermore, an analytical model showed that the cement sheath located between the casing and the reservoir would be exposed to injection and production cycles with high pressure and temperature differentials which demanded a cement system with sufficient flexibility to withstand the mechanical stresses and to optimize expansion to prevent microannulus creation.

Despite the technical and budgetary challenges, methodical planning, the use of new technologies, and engineered optimization resulted in a successful cementing campaign with the required zonal isolation achieved within the project budget limits.

Introduction

To comply with Directive 2003/55/EC of the European Parliament and of the Council for both the electricity and the gas sectors, Hungary reviewed the possibilities of improving the access to the natural gas supply for the customers. Because of heavy dependence on natural gas foreign supplies with uncertainties about seasonal deliverability, the Hungarian government decided to commence drilling and completing a strategic UGS project.

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