APPLICATION OF PETROPHYSICAL MEASUREMENTS TO THE PREDICTION OF SEISMIC RESPONSES OF DIFFERING LITHOLOGYOR PORE FLUIDS1

Abstract

ABSTRACTDetermination of petrography and pore fluid content is an ultimate goal of an integrated seismic‐petrophysical study. For lack of a general inversion technique, forward modelling is useful in studying the relations between lithology, stratigraphy, pore fluid content and the seismic response. This report describes a study of two clastic sequences in Utah, from which 32 rock samples were analysed. A detailed petrographic study was done. Laboratory measurements were made of ultrasonic compressional‐ and shear‐wave velocity as a function of pressure. We computed the velocities at seismic frequencies for the samples when dry, over‐pressured, brine saturated, and oil saturated. The velocities were sensitive to the porosity, carbonate cementation and the depositional facies. We generated velocity profiles for hypothetical reservoirs for a range of saturation states. The velocity profiles were used to generate synthetic seismic shot gathers to study the seismic response of these clastic reservoirs. The fluid‐saturation strongly affects the seismic respone, as does the presence of a coal seam. An amplitude change with offset is often observed. However, stratigraphy appears to have a stronger effect on the seismic response.