f High resolution cross-hole seismic tomography at the Backhorn test facility in Illinois, USA

High resolution cross-hole seismic experiments were conducted at the Backhorn Test Facility in Illinois, U.S.A., where we drilled five 270 m boreholes over the oil producing field for the purpose of various borehole geophysical experiments. According to the exploration and production histories of the field, the oil reservoir is the porous zone of Silurian Kankakee "White Lime" carbonate which is horizontally distributed at the depth of about 200 m, and has no more than 10 m thickness. In fact, two boreholes out of five we drilled produce oil from the Kankakee formation. The results of several kinds of logging measurements conducted just after drilling five boreholes indicate a good correlation between formations from borehole to borehole. However, they also suggest significant lateral changes in porosity within the Kankakee formation.