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University of Split, Croatia Royal Institute of Technology, Stockholm, Sweden

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  1. University of Split, Croatia Royal Institute of Technology, Stockholm, Sweden Hrvoje Gotovac, PhD student RISK ASSESSMENT FROM THE OIL WASTE DISPOSAL IN DEEP WELLS by R. Andricevic, H. Gotovac, M. Loncar and V. Srzic Risk Conference 2008, Cephalonia, Greece, 5-7 May

  2. PRESENTATION • Introduction • Computational setup • Flow and transport analysis of the injected oil waste in deep wells • Risk assessment of the oil waste disposal methodology (exceeding risk) • Conclusions Risk Conference 2008, Cephalonia, Greece, 5-7 May

  3. 1. Introduction Risk Conference 2008, Cephalonia, Greece, 5-7 May

  4. Impermeable cap rock Waste injection Impermeable bed rock Waste spreading waste disposal in a safe and efficiant manner Suitable geological formation prevent wastepropagationto the surfacewith negligible risk of polluting shallow aquifers Risk Conference 2008, Cephalonia, Greece, 5-7 May

  5. Oil waste injection in deep wells Risk Conference 2008, Cephalonia, Greece, 5-7 May

  6. DEEP WELL INJECTION Risk Conference 2008, Cephalonia, Greece, 5-7 May

  7. Risk Conference 2008, Cephalonia, Greece, 5-7 May

  8. Construction of deep well Pi=95 bar Q=250-300 l/min Ph=145 bar Fracture gradient=1,74 bar/10 m Injected up to date 150,000 m3 Marl Sandstone F=15 % Risk Conference 2008, Cephalonia, Greece, 5-7 May

  9. 2. Computational setup Risk Conference 2008, Cephalonia, Greece, 5-7 May

  10. Map of the oil field Žutica (Croatia) Risk Conference 2008, Cephalonia, Greece, 5-7 May

  11. Selection of appropriate geologic formations for oil waste injection in oil field Žutica (Croatia) • 0-500 m (sand and clay layers) • 500 – 1000 m (sandstone and clay layers) • 1000 – 2500 m (sandstone and marl layers) • Injection zone is located at depth around 2000 (m) and consists of sandstone and marl layers Risk Conference 2008, Cephalonia, Greece, 5-7 May

  12. Selection of appropriate deep well for oil waste disposal • Deep well Žutica – 273 • Open holes at 1976-1985 (m), 1994-2021 (m) and 2038-2055 (m) • Injection fluid density is 1006 – 1020 kg/m3, injection time period is 20 years and injection capacity is 30 m3/day Risk Conference 2008, Cephalonia, Greece, 5-7 May

  13. Regression between core horizontal and vertical permeability Risk Conference 2008, Cephalonia, Greece, 5-7 May

  14. 1 5 0 ) V - 1 5 m ( l a j i c - 3 0 n e t o p i - 4 5 n a t n o p - 6 0 S - 7 5 - 9 0 1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0 2 0 5 0 2 1 0 0 2 1 5 0 Depth i ( m ) Spontaneous potential Risk Conference 2008, Cephalonia, Greece, 5-7 May

  15. 280 278 276 274 272 270 pressure, bar 268 266 264 262 260 0 100 200 300 400 500 600 700 800 900 1000 Q_injection m^3/day Injectivity test Risk Conference 2008, Cephalonia, Greece, 5-7 May

  16. 3. Flow and transport analysis Risk Conference 2008, Cephalonia, Greece, 5-7 May

  17. Stochastic approach • Natural variability of the geological formations as well as lack of the measurements • Results are given in the form of two first statistical moments: mean and variance • Spectral method, small perturbation and Monte-Carlo method • For highly heterogeneous formations and oil waste disposal Monte-Carlo is the most powerful and robust method Risk Conference 2008, Cephalonia, Greece, 5-7 May

  18. Risk Conference 2008, Cephalonia, Greece, 5-7 May

  19. Monte-Carlo method for analysis of oil waste disposal in the deep wells • Measurements (geological, laboratory, core tests, slug tests, surface and deep seismic, spontaneous potential, resistance, temperature, sound, tracer injection,…) • Geostatistical analysis of conductivity field and generation of large number of conditional realizations • Flow solution using the conventional finite difference method in the each realization (MODFLOW) Risk Conference 2008, Cephalonia, Greece, 5-7 May

  20. Transport solution in the each realization (PTRACK) • Tracking large number of particles (200 000) • Statistical ensemble averaging over the whole collection of realizations (100) • Results are total mass through top side of the injection zone, displacement and concentration field Risk Conference 2008, Cephalonia, Greece, 5-7 May

  21. Geostatistical indicator analysis of sandstone and marl zones Risk Conference 2008, Cephalonia, Greece, 5-7 May

  22. Geostatistical analysis of the sandstone Risk Conference 2008, Cephalonia, Greece, 5-7 May

  23. Geostatistical analysis of the marl Risk Conference 2008, Cephalonia, Greece, 5-7 May

  24. Final geostatistical analysis of the injection zone Risk Conference 2008, Cephalonia, Greece, 5-7 May

  25. Pressure field Risk Conference 2008, Cephalonia, Greece, 5-7 May

  26. Velocity field in the one chosen realization Risk Conference 2008, Cephalonia, Greece, 5-7 May

  27. Risk Conference 2008, Cephalonia, Greece, 5-7 May

  28. Fraction of the total mass through horizontal control planes Risk Conference 2008, Cephalonia, Greece, 5-7 May

  29. Fraction of the total mass through vertical control planes Risk Conference 2008, Cephalonia, Greece, 5-7 May

  30. Long-term vertical transport analysis Risk Conference 2008, Cephalonia, Greece, 5-7 May

  31. 4. Risk Assessment Risk Conference 2008, Cephalonia, Greece, 5-7 May

  32. Risk assessment (exceeding risk) • Probability that load “L” on the system exceeding the resistance “R” of the system Risk Conference 2008, Cephalonia, Greece, 5-7 May

  33. Risk assessment (exceeding risk) • L - vertical spreading of the injected oil waste • R - vertical position of aquifer for water supply • Alternatively, exceeding risk for some defined time period can be calculated using the travel time pdf Risk Conference 2008, Cephalonia, Greece, 5-7 May

  34. Risk assessment (exceeding risk) • Short-term exceeding risk (pr=10-3 for period t=100 year; Z = 1850 m) • Long-term exceeding risk (pr=10-47 for period t=10000 year; Z = 500 m) Risk Conference 2008, Cephalonia, Greece, 5-7 May

  35. 5. Conclusions • Using all hard and soft input data to reduce uncertainty of the flow and transport analysis • Short-term (pr =10 -3 for period t=100 year ) and long-term exceeding risk (pr =10 -47 for period t=10 000 year ) • Safe and reliable oil waste disposal methodology also appropriate for other hazardous wastes • Consideration of other real physical effects as unsteady velocity fields, sorption or pore-scale dispersion which considerably reduce exceeding risk Risk Conference 2008, Cephalonia, Greece, 5-7 May