What are the objectives of a seismic interpretation? Are the objectives the same today as they were 40 years ago? Certainly today’s 3-D seismic data and computer workstations have added tremendous interpretative abilities that weren’t present 40 years ago—or even dreamed of! However, these are only tools for accomplishing the objectives. Unlike the frequency content of seismic data, the objectives of a seismic interpretation aren’t time varying.
The objectives listed in Fig. 1.A.1 are paraphrased from Jakosky’s book published in 1960. The first objective, “Recognizing a hydrocarbon anomaly,” is still paramount in today’s seismic interpretation. However, our recognition criteria have been greatly enhanced with modern true amplitude acquisition and processing. Seismic amplitude is now one of the major criteria for recognizing potential hydrocarbon reserves.
The second objective, “Validating an anomaly,” might be expanded to include stratigraphic framework through the interpretation of the seismic waveform patterns. However, let’s incorporate stratigraphic validation in the structural interpretation of the geologic framework. In short, find an anomaly, map the structure, and make sure the seismic reflection amplitude is consistent with the structural interpretation.
While the recognition and validation of a potential seismic anomaly might be the interpreter’s objectives, management also has its own. Besides the upside economic value of the prospect, some aspect of risk must be assigned to the prospect, if for no other reason than for trying to decide which prospect to drill first. The management requirement can be stated several ways. One is: “Identify where art dominates and science deviates in the structural and amplitude interpretations.”
Figures & Tables
Seismic Amplitude Interpretation
During the last 30 years, seismic interpreters have routinely applied bright spot and AVO technology for recognizing prospects and predicting lithology. New amplitude attributes were added to this technology as new exploration problems were defined. R&D continues in the field of amplitude interpretation, especially when E&P costs escalate as more severe environments are explored, such as the ultra-deepwater plays. With the high interest in reducing exploration risk, this course addresses the methodology of an amplitude interpretation and the subsequent benefits and limitations that one can expect in various rock-property settings. This book, originally produced for use with the fourth SEG∕EAGE Distinguished Instructor Short Course, begins with a review of relationships between rock properties and geophysical observations. Practical problems illustrate the assumptions and limitations of commonly used empirical transforms, and procedures for conducting and verifying fluid-substitution techniques are presented. The book identifies components of the seismic response best suited for differentiating pore fluid from lithologic effects. Field examples emphasize what combination of seismic signatures should be expected for different rock-property environments. To help select the best seismic attribute for calibrating amplitude to rock properties, rules of thumb are provided for predicting AVO responses and interpreting lithology from observed responses. A case history is also provided. The last part examines the numerous amplitude attributes that can be extracted from seismic data to quantify an interpretation. Benefits and limitations of these attributes in soft- to hard-rock environments are discussed with model data and in case histories.