Jack Dvorkin

The Rock Physics Handbook: Contents

Responding to the latest developments in rock physics research, this popular reference book has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results. It brings together the vast literature from the field to address the relationships between geophysical observations and the underlying physical properties of Earth materials - including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates. This third edition includes expanded coverage of topics such as effective medium models, viscoelasticity, attenuation, anisotropy, electrical-elastic cross relations, and highlights applications in unconventional reservoirs. Appendices have been enhanced with new materials and properties, while worked examples (supplemented by online datasets and MATLAB® codes) enable readers to implement the workflows and models in practice. This significantly revised edition will continue to be the go-to reference for students and researchers interested in rock physics, near-surface geophysics, seismology, and professionals in the oil and gas industries.

Novel Use of P- and S-Wave Seismic Attenuation for Deep Natural Gas Exploration and Development

The well selected for the application of our attenuation theory and extraction of attenuation attributes from seismic data is the Texaco well (API 177104132700) in Block 313 of Eugene Island in the Gulf of Mexico (Well 2700). The rock physics diagnostics indicates that the rock can be described by the uncemented (soft-sand) model. This model is used to predict the S-wave velocity that was missing in the original well data. The Pand S-wave inverse quality factors are computed according to our theoretical model. The ratio of these inverse quality factors (P-to-S) is small (on the order of one) in wet rock and large in the gas zone. The seismically-measured attenuation ratio may serve, therefore, as an indicator of hydrocarbons. The synthetic seismic traces computed using the well data and the ray-tracer with attenuation, specifically developed for this project, indicate that attenuation affects the seismic response and, therefore, can be extracted from real seismic data, including the P-to-P and P-to-S reflection amplitude. Rock Physics Diagnostics – Model for Velocity The gas saturation in the well was calculated from the resistivity curve while the clay content was estimated by linearly scaling the gamma-ray curve between its minimum and maximum values. It was assumed that the formation water has the bulk modulus 2.85 GPa and density 1.01 g/cc while the gas has the bulk modulus 0.14 GPa and density 0.26 g/cc. The total porosity was calculated from the bulk density by assuming that the density tool samples the virgin formation with gas saturation as calculated from resistivity. The measured impedance and P-wave velocity are compared to the curves due to the uncemented (soft-sand) model. The proximity of the data and model (Figure 1) indicates that this model is appropriate for the well under examination. This model was then use to predict the S-wave velocity (absent in the measured data) from the P-wave velocity. The in-situ impedance is plotted versus the total porosity and Poisson’s ratio (PR) in Figure 2 where the data are color-coded by gamma-ray and by water saturation. Similar cross-plots are shown in Figure 3 but for wet conditions where the elastic properties and density were calculated using the P-wave-only fluid substitution. The soft-sand model curves for water-saturated rock are superimposed upon the wet-condition data to further emphasize the relevance of this model. The curves are produced for varying porosity and each for fixed clay content. The latter variable changes from one to zero with step 0.2. These model curves fully encompass the well log data.

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

In this report we will show the fundamental concepts of two different methods to compute seismic energy absorption. The first methods gives and absolute value of Q and is based on computation with minimum phase operators. The second method gives a relative energy loss compared to a background trend. This method is a rapid, qualitative indicator of anomalous absorption and can be combined with other attributes such as band limited acoustic impedance to indicate areas of likely gas saturation.