Features of application of versions of the VSP method for the study of the near-well space
The technology of work, as well as the processing and interpretation of VSP data obtained at one of the sites are covered. The feature of the site is the heterogeneity of the upper part of the section, due to the presence of permafrost. Consideration of this heterogeneity is important for predicting seismic velocities both along the wellbore and below the TD, as well as for linking surface and borehole seismic data. The following set of versions of VSP method was used: zero-offset VSP, offset VSP and moving source VSP. The structure of the near-well space was studied by means of time inversion, as well as by forming images of the medium on longitudinal and converted reflected waves. The revealed inhomogeneity of the upper part of the section in the vicinity of the borehole allowed to correct the obtained seismic images and more accurately estimate the velocities below the TD. At the depth of the studied well about 2 km it was possible to estimate the reality of seismic boundaries to a depth of 5 km and to determine seismic velocities to a depth of 3 km.