A Robust Economic Technique for Crosswell Seismic Profiling

This report is the final report describing work done under research project DEFG03-95ER14504, titled "A Robust Economic Technique for Crosswell Seismic Profiling," which was funded by the U.S. Department of Energy.

The objective of this research program was to investigate a novel way to acquire crosswell tomographic data, that being to use a standard surface-positioned seismic energy source stationed in line with two wells that have downhole receiver arrays. This field technique differs from the traditional way that crosswell tomography is done, which requires that a downhole receiver array be in one well and that a downhole seismic source be in a second well.

Several potential advantages can result from using a surface-based source rather than a downhole source to acquire crosswell tomographic data. Included in these advantages would be: (1) surface-based seismic sources emit more energy than do downhole seismic sources, thus receiver wells can be spaced at greater distances, (2) surface-based sources are more reliable than downhole sources and are more accessible if field repairs have to be done, and (3) downhole receivers can be deployed in a wider range of well conditions (cased hole, open hole, tubing, high-pressure lubricators, etc.) than can downhole sources, allowing crosswell tomography to be done in a wider variety of reservoirs.

However, several potential shortcomings may occur if a surface-based source is used to acquire crosswell tomographic data. The principal concerns are: (1) source-to-receiver ray paths may not traverse the interwell space in a way that allows a robust tomographic inversion to be done, (2) errors in measuring arrival times may be too large for travel time inversion to be stable, and (3) the reduced bandwidths generated by surface-based sources may not allow some interwell targets to be detected.