Introduction to Petroleum Seismology

Excerpt

Seismology is a branch of geophysics that aims for the understanding of earth's interior, through the analysis of ground motion.

The science of seismology began with study of naturally occurring earthquakes. Seismologists soon found that seismic waves produced by earthquakes contained valuable information about earth's interior (crust, mantle, and core). Later they discovered that similar but much weaker man-made seismic waves could be used to interpret the shallow structure of earth, to locate minerals, water, and petroleum resources. Thus, a special branch of seismology known as petroleum seismology and the associated seismic exploration industry were born. To distinguish between petroleum seismology and the study of naturally occurring earthquakes, we will call the latter earthquake seismology.

Although both branches of seismology are based on study of the generation, propagation, and recording of elastic waves in the earth and of the sources that produce them, the job of a petroleum seismologist differs significantly from that of an earthquake seismologist. The advent of 3D seismics — which can produce an enormous amount of detail about subsurface geology and hydrocarbon reservoirs — has changed the job profile of a petroleum seismologist tremendously. No longer isolated to the domain of academic, postdoctoral, or postgraduate researchers or of similarly trained specialists in research centers of the oil and gas industry, petroleum seismologists are widely accepted today as key players in finding petroleum traps and even producing oil and gas more efficiently from complex reservoirs.

In their new role, petroleum seismologists interact with computer scientists, signal processors, petroleum engineers, geologists, and others whose concerns include the simulation, monitoring, and controlling of processes critical to efficient exploration for and production from of petroleum reservoirs. Consequently, the basic background requirements for petroleum seismologists have changed also. They no longer can be assimilated with those of earthquake seismologists, as was once the case at many universities. To accommodate these changes, most geoscience programs worldwide have modified their curricula. However, textbooks to accompany the ever-changing field of petroleum seismology are very limited; Exploration Seismology (Sheriff and Geldart, 1982, revised 1992) is one of the few examples. We hope our book will add significantly to the achievements of Sheriff and Geldart.

This book is derived from lectures given to senior undergraduate and first-year graduate students at Texas A&M University (U.S.A.) and to graduate classes at the Norwegian University of Science and Technology from 1998 to 2003. We have tried to provide students with the basic theoretical background needed to tackle challenges of petroleum seismology, especially those related to seismic data acquisition and processing, to reservoir characterization, and to monitoring of oil recovery based on sensors permanently positioned at the seafloor (4D seismics). Most existing textbooks and syllabi related to petroleum seismology focus on the processing of P-wave energy. In this book, we include a background for processing S-wave energy in addition to that of processing P-wave energy, as emerging technologies. Ocean-bottom seismic (OBS) potentially will provide better access to S-wave energy, therefore leading to better characterizations of reservoirs. We used this basic background to introduce state-of-the-art technology and to discuss possible solutions to some of the emerging challenges of petroleum seismology.

We further emphasize that our goal is to provide readers with the basic background needed to tackle not only present challenges of petroleum seismology but also some foreseeable challenges. The field is spanned fully by several excellent solution-driven texts that our readers can use as specialized applications: Castagna andBackus, 1993; Evans, 1997; Pieuchot, 1984; Spradley, 1984; Stolt and Benson, 1986; Tarantola, 1987; Toksöz and Johnston, 1981; and Yilmaz, 1987, 2001.

The background required for effective reading of this book consists of the typical freshman∕sophomore courses in calculus, elementary differential equations, and geology. It is also helpful but not necessary to have had some exposure to physics.

One of the key features of this book is the use of finite-difference modeling (FDM) to simulate wave propagation and to generate and analyze seismic data. The finite-difference modeling provides the reader with the opportunity to verify theory and to experiment with applications of the techniques studied. For example, in Chapter 2, an FDM simulation of wave propagation is presented to give some concreteness to the basic idea that a pressure source in a homogeneous, isotropic medium can produce only compressional waves.

Another feature is the inclusion of a wide range of examples and problems drawn from different aspects of petroleum seismology, including survey design, data acquisition, and processing. More than 100 problems are included.

We are indebted to those students who have endured preliminary versions of this material, and we invite them to replace those with this updated presentation of course material.