By definition, a seismic attribute is a measurement based on seismic data (Sheriff, 2002). In the strictest sense, then, two-way traveltime, also known as horizon time, is perhaps the most important and frequently used seismic attribute, although it isn't usually considered an attribute.
Brown (1996) includes horizon time in his list of 66 different attributes and indicates that an attribute is “necessarily a derivative of a basic seismic measurement.” He presents a generalized classification scheme that breaks attributes into four categories: time, amplitude, frequency, and attenuation. Brown also poses two questions that all interpreters must address when analyzing seismic attributes:
Figures & Tables
First Steps in Seismic Interpretation
Accurate interpretation of geophysical data — in particular, reflection seismic data — is one of the most important elements of a successful oil and gas exploration program. Despite technological advances in data acquisition and processing and the regular use of powerful computers and sophisticated software applications, you still face a tremendous challenge each time you begin to reconstruct the geologic story contained in a grid or volume of seismic data — that is, to interpret the data. On occasion, this interpretive tale can be clearly told; but most of the time, each page of each chapter is slowly turned, and rarely is the full meaning of the story completely understood.
Where the correlation of one reflection record with another is very easy, little needs to be said. Almost anyone can understand such a correlation. On the other hand, this is a rare occurrence. The usual thing is for the correlation to be so difficult as to be impossible. It is for this reason that correlation procedure can hardly be described in words (Dix, 1952).
Although Dix is speaking about the correlation of individual reflection records, which were used routinely before the advent of continuous common-depth-point (CDP) profiling, he clearly recognized the essence of interpretation as the considered extraction of geologic information from indirect geophysical measurements. His words are no less relevant and applicable now than they were 60 years ago, even in view of the high standards of data quality made possible by advances in seismic acquisition and processing, to say nothing of accompanying developments in interpretation technology. In the modern interpretation environment, you still face correlations that are “so difficult as to be impossible“ because these correlations define the frontiers of opportunity, the ones posing the sternest challenges and ultimately leading to the greatest rewards.
The primary aim of this book is to describe Dix's correlation procedure in terms of the science, data, tools, and techniques now used in seismic interpretation in the oil and gas industry. As an individual geoscientist, you develop and apply your own approach and style when interpreting seismic data. You continually revise and refine correlation procedures during the course of your career and expand them as you complete different interpretation projects. With experience, you learn to check and recheck the validity of your procedures to fully understand the rules of evidence that govern their use:
You must have a good understanding of seismic acquisition and processing principles as well as fundamentals of geology before beginning to collect interpretive evidence and solve interpretation problems correctly.