Images are central to the task of exploring for and producing oil and gas (hydrocarbons) from the Earth’s subsurface. To understand their utility, one must look at both how hydrocarbons are formed and how we explore for them. Oil and gas (hydrocarbons) are generally found in the pores of sedimentary rocks, such as sandstone or limestone. These rocks are formed by the burial of sediment over millions of years and its subsequent chemical alteration (diagenesis). | Image Databases Search and Retrieval of Digital Imagery Edited by Vittorio Castelli Lawrence D. Bergman Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-32116-8 Hardback 0-471-22463-4 Electronic 5 Images in the Exploration for Oil and Gas PETER TILKE Schlumberger-Doll Research Center Ridgefield Connecticut INTRODUCTION Images are central to the task of exploring for and producing oil and gas hydrocarbons from the Earth s subsurface. To understand their utility one must look at both how hydrocarbons are formed and how we explore for them. Oil and gas hydrocarbons are generally found in the pores of sedimentary rocks such as sandstone or limestone. These rocks are formed by the burial of sediment over millions of years and its subsequent chemical alteration diagenesis . In addition to the sediment organic material is also buried and subjected to the same high pressures and temperatures that turn the sediment into rock. This organic material eventually becomes oil and gas. Over time the oil and gas migrates upward through porous and permeable rock or fractures because it is less dense than the surrounding groundwater. Most of these hydrocarbons reach the surface and either evaporate or dissipate. However a small fraction of these migrating hydrocarbons become trapped in the subsurface. A hydrocarbon trap forms when an impermeable rock such as shale lies above a porous rock such as sandstone or limestone. Traps are often associated with faults or folds in the rock layers. The exploration for hydrocarbons generally begins with the search for these traps. Oil exploration may begin with the acquisition of two-dimensional 2D seismic data in an area of interest. These data may be thought of as twodimensional images vertically slicing through the Earth each slice being tens of kilometers long and several kilometers deep. If a candidate area is located on these images then a three-dimensional 3D seismic survey may be acquired over the region. This survey yields a 3D image
