Intrinsic to the WesternGeco Earth model building workflow is the ability to integrate measurements and data across scales within a time frame that has material benefit to reducing the risk and uncertainty inherent to the E&P process. An innovative and powerful application of this fast, integrated, and iterative approach is SGD; a combination of surface seismic depth imaging and anisotropic velocity modeling workflows with the more traditional inversion and reservoir modeling methods. The result is enhanced subsurface definition and improved well placement. Each SGD implementation is customized to the specific requirements of the operator and the subsurface challenges.
The advent of efficient directional drilling instrumentation has significantly reduced while-drilling uncertainty, but often the inability to reasonably forecast the effect of changes in the a priori information used in the well planning phase can result in unplanned events that ultimately cause significant time and cost overruns. The critical factor is the ability to accurately integrate datasets at different scales (e.g., lower-resolution seismic, higher-resolution logging, or LWD measurements) in time to correct the well trajectory. SGD delivers such functionality by applying our in-house cross-disciplinary expertise, advanced tools, measurements, and workflows in a concerted, client-centric manner to provide the driller with actionable, in-time, information. At the core of SGD is the building of a seismic Earth Model which is done at the pre-drill phase.
The adjacent figure depicts the workflows executed during a SGD project to generate a seismic Earth Model. This workflow has the following minimum components:
- Seismic and well data preconditioning
- Borehole data analysis and processing
- 3D seismic depth imaging
- Prestack inversion
- Optionally the incorporation of the seismic Earth model into the mechanical Earth model and reservoir model
Prior to drilling, a volume of interest (VOI) - typically between 25 and 50 km2 - is selected around the planned well. The drilling image can be updated locally in the VOI while drilling, within a project-relevant time frame. This provides ahead-of-the-bit structural, stratigraphic, lithological, and geomechanical information.
With conventional technology, the above workflow could take weeks or months—too long to have any bearing on the well drilling. Working within an integrated environment that harnesses our resident multidisciplinary expertise along with the unique software, workflows, and hardware developed for this application, SGD reduces the time required to reimage such that new measurements can materially influence the drilling operation almost immediately.
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