INTRODUCTION

Lab measurement of physical rock properties can be an important link between in situ measurements of borehole lithology and the information content in remotely sensed surface seismic data. Borehole logs and core data provide direct high resolution measurements of physical properties in the immediate vicinity of a well bore. Surface seismic data, on the other hand, offer a relatively lower resolution measurement of earth material properties, but over a much larger area or volume scale. Lab measurement of seismic responses in rock core samples can help illuminate the role of pore geometry and pore fluid type/saturation in determining the velocity and impedance information extracted from surface seismic data. Core sample measurements, coupled with a suitable rock physics model, can also be useful in predicting unmeasured physical behavior. Estimation of saturated velocity or so-called fluid replacement calculations using the Gassmann Equation are such examples commonly used in D&P reservoir geophysics analysis.

In the classic paper by Castagna et al. (1985), the authors develop empirical / relationships which identify various rock types by combining data from lab core, in-situ sonic, and field seismic measurements. Furthermore, Castagna et al. find that the Gassmann relation accurately predicts saturated velocities from dry rock measurements, especially when the dry shear modulus $\mu_d$ is about equal to the dry bulk modulus K_d. These combined results are important in reservoir geophysics work, in order to calibrate field seismic data to well log information and core sample data, and so potentially map out changes in lithology, pore geometry, pore fluid, and pore saturation in the reservoir target zone. As an excellent example, Lucet and Mavko (1991) integrated rock physics lab measurements with cross-hole velocity tomograms and well logs, and mapped images of porosity and shale content in a reservoir zone.

The purpose of our exercise was to get some ``hands-on'' experience in making rock physics measurements on rock samples in the laboratory. Our paper proceeds as follows. First we briefly describe the experimental setup. Next, we discuss the experimental procedure, and the measured data. The third section concerns our and velocity calculations and error analysis, including our Gassmann predictions of saturated and from the dry Massillon sandstone sample. Finally, we end with a discussion of our results and a summary.