Revealing the Geology of the Gulf of Mexico Recorded by 3-D Seismic
Authors: Maione Steven J. 
Published: October 2008

Many visionaries in the geophysical field have realized that 3-D seismic data contains a wealth of information about the subsurface geology, which up until now has not been fully exploited. It is in this light that Coherence Cube? processing, a 3-D seismic imaging tool, provides the seismic interpreter, geologist, and reservoir engineer with the ability to interrogate the seismic volume to identify, and map important components that define a hydrocarbon trap. The ability to reveal critical features such as faults, lithologic boundaries, and reservoir compartments within the seismic bandwidth is a major step forward in exploiting 3-D seismic. Comparison of conventional seismic and Coherence Cube processed images from 3-D seismic volumes in the Gulf of Mexico on salt domes and in stratigraphic complexes demonstrates the interpretive advantage Coherence Cube processing offers the petroleum industry. Since becoming available in 1995, Coherence Cube processing has significantly evolved and matured into an element necessary for successful hydrocarbon exploration and development in the Gulf of Mexico, and throughout the world.

Introduction

Although conventional migrated 3-D seismic data is imaged from the standpoint of collapsing diffractions and placing reflectors in their correct relative positions, the standard 3-D seismic volume does not produce clear images of faults and stratigraphic information. Thus, the seismic interpreter has to use his or her "interpretive license" in order to interpret or deduce the geometry and expression of various geologic features, such as faults and stratigraphic discontinuities. The standard 3-D seismic volume certainly shows seismic disturbances where large-displacement faults and significant stratigraphic discontinuities are present (Fig. 1), but these seismic features range in size from easily resolvable downward to the detectable limit, diminishing the chances that the interpreter will recognize all of them. Recognition and mapping of these seismic features in three dimensions and interpretation of their geologic significance are required to successfully describe a hydrocarbon trap. With conventional seismic interpretation using time slices, a common experience is faults with little vertical displacement, or are parallel to structural strike, are virtually impossible to identify and map. Fault interpretation process is often sidetracked into a period of laborious crossline, inline, and arbitrary line interrogation. Mapping of stratigraphic features is difficult and time consuming as well, resulting in only partial extraction of the wealth of stratigraphic information residing within the 3-D seismic volume.

First introduced to the oil industry by Mike Bahorich and colleagues at Amoco,1–3 Coherence Cube-based 3-D processing has evolved and developed into an indispensable tool that effectively extracts a vast amount of information from the 3-D seismic data volume that would otherwise be overlooked. Coherence Cube processing provides an ability to measure three-dimensional spatial variations in the seismic waveform with dip comprehension. The basic seismic waveform is a measure of time, frequency, amplitude and absorption. These spatial variations are the seismic response to lateral variations in the physical and geometric properties and characteristics of the rocks. Measuring these combined changes in the seismic responseallows the interpreter to physically locate and map these changes in 3-D space. The Coherence Cube measurement is an attempt to capture these changes. Coherence Cube processing provides the seismic interpreter, geologist, and reservoir engineer with a tool and technique that significantly improves productivity and accu