Characterization of Lithology Using Crosshole Methods

A cross hole data log has been recorded in a producing oil field in the Permian Basin of west Texas. This log consists of traces at 3 m depth Increments recorded from horizontally propagating waves between two wells spaced 304 m apart in a carbonate reservoir. The recorded data contain frequencies up to the cutoff frequency of 3000 Hz even at this long offset. Vp, Vs, Vp/Vs, and Ap/As calculations were made from first arrival times. Vp and Vs values plotted on a "Pickatt diagram" indicate limestone or dolomite lithology. A plot of Vp/Vs and porosity from the receiver well shows a clear inverse correlation indicating that crosshole Vp/Vs has the potential for high resolution of lithology parameters. Ap/As calculations from the crosshole log show two distinct zones: a zone of high Ap/As values at depths from 1311 to 1372 m and a zone of lower values over the remainder of the depth range. We have interpreted the higher Ap/As values' as a fluid-filled zone. a values have been calculated from a set of high frequency crosshole data recorded In a shallow clastic sequence in an oil field in south Texas. Using a piezoelectric bender as a downhole energy source and a single hydrophone receiver, data were recorded over a depth interval from 152 to 180 m In 3 m Increments. Data were recorded using three Inllne wells to provide well offsets of 15 m and 61 m. These data were then analyzed to determine a using the spectral ratio method. Q values averaged for all frequencies at the various depths range from 43 to 128. A comparison of a values with a resistivity log from the source well showed a high Inverse correlation. The high a values have been interpreted as shale zones and the Iowa values as sandstones.