Virtual source: new method for imaging and 4D below complex overburden

Abstract

Complex overburden is responsible for a variety of seismic imaging/4D problems. Sometimes overburden complexity simply prevents us from imaging the deeper subsurface. We are unable to sufficiently sample and accurately build and honor near‐surface velocity models. We propose an alternative solution that does not require knowledge of the near‐surface velocity model. The price to pay is placing geophones in the Earth below the most complex near‐surface part while keeping sources at the surface. Receivers may sit in horizontal or slanted wells, which may be producers/injectors or dedicated side‐tracks. Utilizing time reversal logic, we convert surface‐to‐downhole data into a new dataset with downhole Virtual Sources (VS) located at geophone positions. The resulting VS dataset with both downhole sources and receivers can be conventionally imaged requiring only the bottom portion of the velocity model below the receivers that is more simple to obtain. To illustrate the technique, we show application to one synthetic data set and one field case study.