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