AN EXAMPLE OF ACOUSTICS AND VERY HIGH-RESOLUTION SEISMIC IN A HIGHLY DEVIATED WELL

Acoustic logging is conventionally used to determine the slowness of f ormations. The total-field recordings made in highly-deviated or horiz ontal boreholes can be processed to provide microseismic borehole cros s-sections having a lateral investigation range of some ten meters aro und the drain hole. This article describes the results of experiments performed in a limestone quarry located in Burgundy, France. A highly deviated borehole (10 degrees) was drilled into a ''white oolite'' geo logic unit that was about 80 m thick. Acoustic logs and high resolutio n seismic were recorded in the deviated borehole. In acoustic logging, two sets of data were recorded: a constant-offset cross-section and a common shotpoint with a great number of traces and a centimetric dist ance between traces. Data processing brought out reflections inside th e white oolite several meters away from the drain hole. The acoustic l og was not able to determine the top and bottom of the white oolite un it. This goal was partially achieved by very high resolution seismic i n the borehole. This type of seismic works in a frequency band interme diate between conventional borehole seismic and acoustic logging. It r equires the development of special tools, particularly with regard to the borehole sources. A common shotpoint gather of very high-resolutio n seismic data obtained with a prototype source of the impulsional typ e shows reflections corresponding to reflectors situated several tens of meters (approximately 40 m) away from the drain hole. The results o f these experiments showed the potential of acoustic logging and high- resolution borehole seismic for describing a reservoir unit at differe nt scales.