Real geological surfaces are not smooth and continuous. Looking at that image just emphasize that declaration. You can see faults, movements of interfaces, fractures of different scale, size and direction. It varies from 1 mm to several hundred meters. All of that have huge implication on the interpretation that we are doing during the exploration and production process. For example, knowing the direction of the fault or fractures play crucial role on the decision where to put a rig and how to do that.At the same time most of modern imaging methods including PSDM and PSTM are looking for smooth and continuous interfaces as part of its QC routine. Normally, small scale heterogeneities in the subsurface are detected by visual interpretation of the imaging(manual or automatic) which is indirect procedure. On other hand seismic wavefield contain direct information about those small scale objects. This information encrypted in Diffraction energy. So, in case we would find a way to detect and image that energy, we found the key for that code. This presentation presents a way how to do that using MultiFocusing method.So the motivation is pretty simple – the industry would like to know where the fractures, faults and salt flanks are.
Target orientedOptimization was done in order to be in reasonable timeframesDiffractivity clouds might indicate directly fractured and faulted zones.
Conventional stackCommon Reflection / Depth Point Stacking SHOTS RECEIVERS 2 x2 t t 0 REFLECTOR V2 COMMON REFLECTING POINT
Conventional stack Normal move out equation is valid when only traces with equal distance to shot and receiver are stacked within a CDP gather (red) v Receiver coordinate v + v + + + v + + v + ++ + v + v + v + + Shot coordinate CMP position + CMP traces + MF traces
MultiFocusing move-out correctionMultiFocusing time correction formula is valid for arbitrarysubsurface structure and for arbitrary source-receiverconfigurations 2 (R )2 2 R X s sin Xs R (R )2 2 R X r sin Xr 2 R V0 V0 X s and X r source and receiver positions R ( RCRE , RCEE , ) are the radii of curvature of the wavefronts ( RCRE , X 0 , X s , X r , ) focusing parameter is the emergence angle of the normal ray
2D MultiFocusing – 3 parametersCRE Radius & CEE Radius and emergence angleRcre – radius of curvature of common reflection elementRcee – radius of curvature of reflected surface
MultiFocusing stack The MF sums the data along the MF stacking surface
MultiFocusing stack Normal move out equation is valid when only traces with equal distance to shot and receiver are stacked within a CDP gather. Nearby traces (green) can not be used but are utilized by our MultiFocusing™ methodology. Receiver coordinate v v + v + + + v + + + + + v + ++ + + + + v ++ + + + + + v + + + + ++ + v + + + + + + v Shot coordinate CMP position + CMP traces + MF traces
Velocity corridor picking z0-Δz Wavefront X0 t0+Δt Xi z0 z0+Δz t0 X0 Xi X t0-Δt β TIME Rcre DEPTH Reflector
Enhanced MultiFocusing gathers MF stacking surface AThe MF sums the data along the green surface. The partial MF sums the dataaround the specified point (point A). The partial MF is shown in red coincideslocally with the MF stacking surface.
Diffraction - definition Obstacle Wave frontA diffraction occurs when a wave encounters an obstacle.In classical physics, the diffraction phenomenon is described as the apparent bending of wavesaround small obstacles and the spreading out of waves past small openings.Research suggests that this can be used to map fractures in the sub-surface fromseismic.