Duplex Wave Migration TetraSeis Inc. 1 A study of vertical heterogeneities using Duplex Wave Migration (DWM)
Outline 2 Introduction Background Conventional Method Duplex Wave Migration DWM Method DWM Advantages CI Seismic Image DWM Seismic Image CI Seismic Image 2 DWM Seismic Image 2 DWM Result 1 DWM Result 2 Building sub-vertical boundaries Interpretive Workflow DWM Example Reverse Time Migration vs. Duplex Wave Other Approaches to DWM DWM Resolution Yemen Case Studies Conclusion References
Introduction Until recently it had been assumed that seismic imaging of the sub-vertical boundaries did not have a solution. This has been due in part to the fact that waves reflected from sub-vertical boundaries never reached the surface. VSP presented good possibilities, however the information received from the vicinity of the borehole is very limited. 3
4 Background Conventional 3D anisotropic Prestack Depth Migration (PSDM) provides accurate structural boundary information for events with dips 0 to 60. Duplex Wave Migration (DWM) is a newly developed technology capable of imaging events with dips 60 to 90. DWM reinforces the Conventional methods by building stacks on sub vertical boundaries. PSDM Sub Horizontal Boundaries DWM Sub Vertical Boundaries PSDM reinforced by DWM in reducing seismic image uncertainties
5 Conventional Method Reflected (one bounce) waves don t reach the seismic acquisition surface.
6 Duplex Wave Migration (DWM) Even in the absence of strong vertical velocity gradient, which is very common you can image steep boundaries. Duplex waves are strong enough to be used for geological purposes. Duplex waves get reflected twice: 1. From a sub-horizontal surface 2. From the target sub-vertical surface
7 DWM Method Duplex waves get reflected twice: 1. From a subhorizontal surface 2. From the target subvertical surface
DWM Advantages 8 Great for displaying and recognizing geological structures with slopes of 60 to 90. Salt wall topography imaging Weak amplitude faults Fracture zones Sub-vertical heterogeneities And much more It doesn t require a large recording aperture. Enhancement in well planning, well productivity and well workovers.
CI Seismic Image 9 Salt walls and sealing fractures could easily be misinterpreted or missed. Seismic image along Y=8600 obtained by conventional 3D Migration
DWM Seismic Image 10 Great detail on sub vertical structures. Salt walls and Fractures are clear. Seismic image along Y=8600 obtained by DWM 3D Migration
CI Seismic Image 2 11 Seismic image along Y=10800 obtained by convention al 3D Migration
DWM Seismic Image 2 12 Seismic image along Y=10800 obtained by convention al 3D Migration
DWM Result 1 13
DWM Result 2 14 Better subsurface control due to better subsurface interpretation.
15 Good sub-vertical interpretation Building of Sub- Vertical Boundaries DWMI Best Interpretation Results CI Good sub-horizontal interpretation The following displays PSDM data as well as DWM complimentary data on sub vertical structures.
16 Depth Model Prestack Data CI PSDM (Dips 0-60 degrees) Depth Model Prestack Data Interpretive Workflow Forward Modeling DWM (Dips 90 degrees 30) DWMI Post Processing Interpretation + Initial Integration of the Conventional Interpretation (CI) and Duplex Wave Migration Interpretation (DWMI) workflows. Integrate DWMI results with the original depth model obtained by CI methods No Yes Do DWMI results tie with "known" CI results Does the depth model change significantly? No
17 DWM Example Duplex Wave Duplex Wave Salt Stock Duplex Wave Duplex Wave
18 Reverse Time Migration (RTM) vs. Duplex Wave Migration (DWM) It also requires more resources, both manpower and processing equipment.
19 Other Approaches to Sub-Vertical Imaging Shows more accurately the tectonic macrofracturing between wells 2 and 7.
20 DWM Resolution
21 Yemen Case Study Overlay both methods. DWM andit PSDM. Shows the PSDM. Shows View (z) theof injector DWM. Shows well inblue. the blue. XTop view of DWM and PSDM overlay. DWM. Shows the injector well in PSDM showthe the location of be location ofinterpret injecting well in cannot relation to Fault is hard of to injecting interpret well and in relation to Shows the location of injecting well in islocation easier todata Fault as well as injecting well. the fault. seen the accurately. fault. relation to the fault. notice any other missed fractures.
22 Conclusion DWM is a complimentary process reinforcing Pre-Stack Depth Migration (PSDM). DWM is great at displaying geologic structures displaying steeper than 60 angles. Duplex wave migration (DWM) in difference from Refracted wave migration do not require velocity model with considerable vertical gradient and big source - receiver offsets. TetraSeis is the proprietary of the DWM method patented in the USA in 2005.
23 References TetraSeis DWM material: Papers and presentations. Mamalevskyy Naum. 2010. A study of vertical heterogeneities using Duplex Migration (DWM). Tetrale Group Inc. Introduction to Duplex Wave Migration. Client Guide. Tetrale Group Inc.