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Main topics Microseismicity caused by hydrocarbon production and storage, and by CO2 sequestration Wadati’s method in wells ... ... and joint 3D tomography by active and passive seismic, from well and surface receivers
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Joint 3D relocation of earthquakes by surface and borehole
data
Aldo Vesnaver&Lara Lovisa Trieste, 7 October 2008 Annual
Meeting of the Italian EAGE-SEG Section Main topics Microseismicity
caused by hydrocarbon production
and storage, and by CO2 sequestration Wadatis method in wells ...
... and joint 3D tomography by active and passive seismic, from
well and surface receivers Method Voxels in irregular grids Ray
tracing for direct, reflected,
refracted, diving and converted waves Method 1. Time Zero by
Wadatis method (or Least Squares)
2. Initial model from 3D seismic, well data and geology 3.
Hypocentre estimate by Shrinking Grids 4. 3D tomography 5.
Iterations of steps 3 and 4, until convergence Method 1. Time Zero
by Wadatis method (or Least Squares)
2. Initial model from 3D seismic, well data and geology 3.
Hypocentre estimate by Shrinking Grids 4. 3D tomography 5.
Iterations of steps 3 and 4, until convergence Wadati in a well ?
Wadati in a well ? Wadati in a well ? Wadati in a well ? Rp, Rs =
Recorded P or S time
Tp, Ts = Actual P or S traveltimes Vp, Vs = Average P or S velocity
To = Time Zero Method 1. Time Zero by Wadatis method (or Least
Squares)
2. Initial model from 3D seismic, well data and geology 3.
Hypocentre estimate by Shrinking Grids 4. 3D tomography 5.
Iterations of steps 3 and 4, until convergence Method - Shrinking
grids 3D recording geometry 225 receivers at surface 28 receivers
in 2 wells
(Jervis and Dasgupta, 2006) (Dasgupta, 2006) 3D recording geometry
Vertical arrays Area : 3 x 3 km
Maximum depth : km Relocation 1.5D model (true traveltimes, without
Wadati) NonLinLoc
Hypo3D Relocation 3D model Missing (true traveltimes, without
Wadati)
NonLinLoc Hypo3D Method 1. Time Zero by Wadatis method (or Least
Squares)
2. Initial model from 3D seismic, well data and geology 3.
Hypocentre estimate by Shrinking Grids 4. 3D tomography 5.
Iterations of steps 3 and 4, until convergence Synthetic model P
velocity km km/s Reflection tomography
P velocity km km/s Active + passive tomography
P velocity km km/s Synthetic model S velocity km km/s Reflection
tomography
S velocity km km/s Active + passive tomography
S velocity km km/s Conclusions Wadatis Method does NOT work in
wells
and if the Vp/Vs ratio changes a lot along the ray-paths of
recorded events Thus, surface and well data should be jointly
processed for the Time Zero The joint 3D tomography of active +
passive seismic can better image the reservoir Gualtiero (Walter)
B
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