Time lapse seismic - past and future

Transcription

1 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 ( ) IOR Norway 2015 M. Landrø

2 3D seismic the major break through

3 Two complementary 4D analysis techniques Top reservoir No changes OWC Amplitude changes Time shift Oil- filled reservoir Amplitude changes and 7me shi8s

4 The breakthrough: Predicting water front movement from 4D seismic C 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

5 4D Seismic Analysis - from detailed trace by trace comparison to map view of differences Comparison ( ) after 9 years of oil production amplitude change at OWC is caused by water replacing oil Difference ( ) - vertical profile Top reservoir OWC Top reservoir Difference ( ) - 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)

6 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 $ D-wells drilled

7 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 bar

8 Grude et al., SEG 2012 Inverted changes in satura7on and pressure ΔP Using near and far stacks ΔS Brie e=3

9 Seismic monitoring of an underground blowout: Well 2/4-14 leaks 326 days in 1989 Relief well (1.2 km away) Well head pressure

10 SE 1988 Brute stacks line 804 2/4-14 NW ms anomaly 2009 Less pulldown in 2009 slight increase in horizontal extention

11 4D difference after global scaling Shallow gas? Multiple of 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

12 Line crossing both wells (14=blowing; 15= relief) 2-4/15 2-4/14

13 Migra7on of gas in 490 sand from 1991 (blue line) to m

14 Overburden monitoring: Amplitude map (top of 10 m 600 m depth) brightening caused by shallow gas

15 Ice scours and pock marks in the Barents Sea 60 m Depth of ice scour is 8 m From

16 Greenland ~ Norway 1-2 Myears ago: Ice berg ploughmarks Photo: Helge Løseth

17 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

18 4D effects: gas movements in overburden Haavik and Landrø, 2014

19 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

20 PRM: Permanent Reservoir Monitoring - Increased cost - Improved repeatability - More possibili>es: Record noise, 4D refrac>on, Fields in Norway: Valhall, Ekofisk, Snorre and Grane AND JOHAN SVERDRUP

21 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,

22 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

23 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