Rejuvenation of a mature oil field: Underground Gas Storage and Enhanced Oil Recovery, Schönkirchen Tief Field, Austria IEA-EOR Conference 2009 Torsten Clemens, Joop de Kok, Yannick Yanze

Gas supply shortage in 2008

Outline Reservoir overview Concept Underground Gas Storage (UGS) + Enhanced Oil Recovery (EOR) Simulation setup Optimization of UGS Dewatering Cycling EOR Conclusions

Reservoir overview Highly fractured dolomite Water- to mixed wet 19 mn Sm3 STOIIP GOC at 2550 mss OWC 2740 mss Producing since 1962 Current recovery factor 59 % Water flooded

Historical production – initial conditions

Historical production – initial oil production phase

Historical production – initial oil production phase

Historical production – perforation higher

Historical production – water injection

Historical production – current conditions

Historical production – current conditions Sorw = 25%

Underground Gas Storage & EOR - fractures

Underground Gas Storage & EOR - fractures

Underground Gas Storage & EOR - fractures

Underground Gas Storage & EOR - matrix Sorg = 15% Sorw = 25%

Simulation setup Is it possible to build up the required volumes of gas? How long does it take to build up the UGS? Is dewatering required? How much cushion gas is required to safely produce the gas volumes? How many wells are necessary to inject and produce the required gas volumes? Where to place the injection / production wells? What are the risks and uncertainties? Is there any EOR potential? Is there an opportunity to accelerate current production?

Simulation setup Dual-permeability approach: two superimposed grids Matrix grid Fracture grid km, fm kf, ff, σ input properties fracture-fracture exchanges matrix-matrix exchanges matrix-fracture exchanges Pm, Sm Pf, Sf unknowns

History match Multiple history matches Multiple predictions

Optimization of UGS – phased approach 3 Phase 1 2 Total injected gas [billion m³] 1 0.5 2.5 5.5 Time in years

Optimization of UGS – phased approach 3 Phase 1 Monitoring phase 2 Total injected gas [billion m³] 1 0.5 2.5 5.5 Time in years

Optimization of UGS – phased approach 3 Phase 1 Monitoring phase 2 Total injected gas [billion m³] 1 0.5 2.5 5.5 Time in years

Dewatering to increase gas volume 1.8 1.5 1.2 Without dewatering 0.9 Total injected gas [billion m³] 0.6 0.3 0 0.1 0.2 0.3 0.4 0.5 Time in years

Dewatering to increase gas volume 1.8 With dewatering 1.5 1.2 Without dewatering 0.9 Total injected gas [billion m³] 0.6 0.3 0 0.1 0.2 0.3 0.4 0.5 Time in years

Dewatering to increase gas volume Water injection into sandstone Horizontal gas injection wells Original oil/water contact Vertical dewatering wells

Gas/liquid contact movement in the fractures

UGS & EOR - concept Crestal gas injection wells Oil rim Residual oil 15 % Residual oil 25 % Original oil/water contact Downdip production wells

Enhanced Oil Recovery (EOR) 2008 2030

Enhanced Oil Recovery (EOR) Production of incremental oil after several cycles Up to 5 % recovery of incremental oil in place

Effect of gas cycling on oil production

Gas/Oil Contact in Fractures and Matrix Gas Injection Gas Production Gas invasion in matrix Gas invasion in matrix Gas/Oil Gravity Drainage in Matrix Gas/Oil Gravity Drainage in Matrix Gas/Oil Contact in Fractures Well Well Water/Oil Contact in Fractures

Conclusions Schönkirchen Tief is good candidate reservoir for high performance Underground Gas Storage 1.5 bn m³ gas can be injected in phase one and 3 bn m³ gas in phase two (dewatering required)

Conclusions Schönkirchen Tief is good candidate reservoir for high performance Underground Gas Storage 1.5 bn m³ gas can be injected in phase one and 3 bn m³ gas in phase two (dewatering required) De-watering can be optimised by drilling vertical wells deep below the original oil/water contact Enhanced Oil Recovery can be achieved due to the difference in residual oil saturation towards water and gas Up to 5 % incremental oil can be recovered

Acknowledgements Thanks to: OMV E&P for the permission to publish this paper