Gas supply security or enhanced gas recovery?

In January 2006, a serious havaria situation emerged in the gas transmission of Central Europe due to the dispute between Ukraine and Russia leading to a shutdown of gas supplies.

Therefore the Hungarian Parliament passed a bill on strategic gas storage, after which the Hungarian government called for a tender in the implementation of strategic underground gas storage. The tender winner MOL Plc. has planned and developed a 1.2 Bn m3 working gas capacity underground gas storage which has 20 Mm3 daily peak capacity even for as long as 45 days. The planned UGS is situated in the SE part of Hungary, in the Algyô field, which is the largest hydrocarbon accumulation in the Pannonian Basin. The initial GOC refers to 1756 mss depth. The reservoir can be found in the uppermost sandstone series showing good reservoir quality. The well sortiered, middle and coarse grain sandstone contains saturated light oil (0.32 cP, 45 API) reservoir with significant gas cap. Initial resolved gas ratio is 121m3/m3 at 182.5 bar reservoir pressure. The initial C3 and C4 content of the gas cap is 4.3 mol% while the C5+ content is also above 3.5 mol%. During the 41 year-long exploitation history, water injection at GOC technology had been used for improvement of the oil recovery factor following primary depletion mechanism. As a result of the IOR technology, 41.7% recovery factor was reached by December of 2006. The reservoir management had dual aims.
One of the aims was to establish an underground gas storage matching the tender conditions and meeting strategic requirements. The second aim was to introduce an EGR process by recycling dry working gas leading
to an increase in the recovery of mid hydrocarbon components from the gas cap and the accelerated production of condensate. A 3D, compositional simulation model was developed to evaluate the potential of the gas
cycling. During the up-scaling of the static geological model, certain flowing units and rock bodies were identified in identical and interconnecting depositional environment. Comparing the production forecast cases due to
the introduction of EGR gas injection it allowed for an additional 39.6 km3 condensate increase and 46.2 km3 advanced condensate production until 2010. It is planned to drill an additional 44 wells and to complete them with 5” diameter of tubing size, which number includes 10 horizontal wells. In order to avoid sand control problems the wells will be gravel packed. The development of UGS is very ambitious since the strategic volume has to be available by January 2010. This case study summarizes the planning and the preparation of the gas cycling and the UGS development project and the potential for handling existing risks, as well as it highlights what
additional benefits can be reached by the application of the reservoir management improving efficiency of the UGS dramatically.

Gyula Nagy, Lajos Benedek, Veronika Pipicz, István Papp, Mária Ósvay Hnisz, Ilona Tóth Varga, János Geiger