Time lapse seismic - past and future «The great book, always open and which we should make an effort to read, is that of Nature», Antoni Gaudi (1852-1926) IOR Norway 2015 M. Landrø
3D seismic the major break through
Two complementary 4D analysis techniques 1985 1995 Top reservoir No changes OWC Amplitude changes Time shift Oil- filled reservoir Amplitude changes and 7me shi8s
The breakthrough: Predicting water front movement from 4D seismic 95-85 C-36 96-85 C-36 B-12 started water injection in 1991 Water front moves slow (100 m/ year) pressure fronts faster B-12 B-12 The well observations confirmed the 4D interpretation
4D Seismic Analysis - from detailed trace by trace comparison to map view of differences Comparison (1985-1995) after 9 years of oil production amplitude change at OWC is caused by water replacing oil Difference (1985-1995) - vertical profile Top reservoir OWC Top reservoir Difference (1985-1995) - map view at oil-water contact red indicate high production between seismic surveys "light" indicate minimal drainage in the production period Oil-Water Contact (OWC)
Important to bring 4D into a FIELD perspective in a timely manner: Initial 4D identification of undrained oil 2.5 km Estimated net value of 4D at Gullfaks is 1 billion $ - 19 4D-wells drilled
Time lapse AVO => Saturation and pressure changes top reservoir OWC Saturation changes Pressure changes - 27% of remaining reserves in this segment has been produced - Pressure anomaly crosses the OWC and terminates close to faults - Observed pore pressure increase in the segment is 50-60 bar
Grude et al., SEG 2012 Inverted changes in satura7on and pressure ΔP Using near and far stacks ΔS Brie e=3
Seismic monitoring of an underground blowout: Well 2/4-14 leaks 326 days in 1989 Relief well (1.2 km away) Well head pressure
SE 1988 Brute stacks line 804 2/4-14 NW 1990 520 ms anomaly 2009 Less pulldown in 2009 slight increase in horizontal extention
4D difference 1990-2009 after global scaling Shallow gas? Multiple of 520 520 ms anomaly 650 ms anomaly Useful both for detec7on of shallow gas and CO2- monitoring: A8er 20 years most of the gas is s7ll in subsurface sand layers
Line crossing both wells (14=blowing; 15= relief) 2-4/15 2-4/14
Migra7on of gas in 490 sand from 1991 (blue line) to 2005 200 m
Overburden monitoring: Amplitude map (top of 10 m sand @ 600 m depth) brightening caused by shallow gas
Ice scours and pock marks in the Barents Sea 60 m Depth of ice scour is 8 m From www.mareano.no
Greenland ~ Norway 1-2 Myears ago: Ice berg ploughmarks Photo: Helge Løseth
Ice scours create traps when the intersect dipping layers Ice scours orienta>on to North, sand layer dipping to West => perpendicular direc>ons Haavik and Landrø, 2014
4D effects: gas movements in overburden Haavik and Landrø, 2014
4 D refrac7on 7meshi8 analysis Close to well Away from well B M B M Field data (SAGA well 2-4) Refracted wave Gas accumula7on caused by blow out Zadeh and Landrø, 2012
PRM: Permanent Reservoir Monitoring - Increased cost - Improved repeatability - More possibili>es: Record noise, 4D refrac>on, +++ 4 Fields in Norway: Valhall, Ekofisk, Snorre and Grane AND JOHAN SVERDRUP
4D refrac7on seismic 1899: Cargill Gilston KnoX describes and explains propaga>on, refrac7on and reflec>on of seismic waves at subsurface boundaries. In 1962 Markvard Sellevoll at the University of Bergen acquired toghether with the Universi>es of Copenhagen and Hamburg acquired a refrac>on seismic survey in Skagerak, south of Norway. Landrø et al., 2004, Time lapse refracoon seismic a tool for monitoring carbonate fields?, SEG, 2295-2298.
Time lapse refrac7on radar Permanent receivers Reservoir monitoring: - Refrac7ons from top/base reservoir - Rig source fired every day - Measure 4D 7me shi8s and amplitudes - Mul7azimuthal analysis 4 km 8 km Overburden monitoring: - Leakage detec7on - Pressure build ups - Stress/strain changes - Disposal wells (waste injec7on) N 5 km Method is sensi>ve to velocity varia>ons 1682 m 1794 m
4D geophysical challenges 4D seismic has resolu7on to 10 m in both direc7ons want to push this limit further 4D seismic Established and useful Challenges: Repeatability, con7nuous monitoring, lower costs, simpler solu7ons More focus on overburden Permanent systems and towed solu7ons will both be used 4D gravity, electromagne7cs will be used 4D seismic and reservoir simula7on