To gain additional information about the subsurface, seismic surveys, and in particular Vertical Seismic Profiles (VSP), are an established geophysical method. Using a well-coupled, vertical array of 3C geophones, a VSP survey records full waveform P- and S-wave signals originating from surface-based sources, and inherently reveals valuable information about the structure and lithology of a reservoir.
Historically, VSPs have been used to connect time-based surface seismic data with depth-based well logs. Due to advances in equipment and processing, a wealth of information can now be derived from VSP data that relates to reservoir conditions including heterogeneity, anisotropy, rock properties and the presence of natural fractures.
By bundling the services together, operators can take advantage of cost savings associated with the fact that a downhole geophone toolstring is already rigged in to the well for microseismic acquisition.
A VSP survey can be a logical add-on for operators who may benefit from VSP results without the extra expense of stand-alone services.
VSP is also particularly helpful in situations using ESG’s patented Hybrid™ monitoring configuration, where seismic sensors tuned for different frequency bandwidths are deployed simultaneously in boreholes and on the surface.
By providing insight into lithological layers outside the immediate treatment zone, VSP results can improve earth models above depths normally logged by wireline tools.
Microseismic processing requires a well calibrated velocity model that accurately estimates subsurface conditions. Integrating VSP data into microseismic processing helps to improve the accuracy of these velocity models, and in turn, microseismic results.
Initial microseismic velocity models are often developed using dipole sonic logs, however VSP surveys allow for more accurate modeling of frequency dependent velocity variations within the reservoir. After generating an initial velocity model, ESG then refines the model using advanced velocity inversion for further calibration.