AVO: Seismic Lithology
by Mike Graul and Fred Hilterman
Duration: Two days
Intended Audience: Entry and intermediate levels
Prerequisites (Knowledge/Experience/Education Required): The course is designed to be followed by anyone with a broad geoscience background: no specific detailed foreknowledge is required, although a familiarity with geophysical terminology will be useful.
The concept of using amplitude variations with offset (AVO) for the direct detection of hydrocarbons was first reported to the geophysical industry in 1982 by Bill Ostrander. Since then, the interest in this technique has continued with multiple sessions at the SEG Annual Meeting, special issues of The Leading Edge, dedicated seminars, and specialized processing and interpretation packages. While there have been many significant technical advances and improvements in our understanding of this subject, there is still much in the way of mysticism and misconception in its treatment and implementation throughout the industry. The goal of this seminar is to update the geophysical community on the current state and future trends of AVO (e.g., azimuthal AVO, "Fizz water" discrimination, shale prospects) and to dispel the mythology which has attached itself to this valuable technique.
Case histories illustrate methodology; exercises and workshops are used frequently to focus on the practical aspects of AVO in predicting lithology and pore fluid. Emphasis is placed on the balance of potential and pitfalls of this technology.
- In different depositional environments:
- Develop velocity versus porosity transforms for sensitivity analysis of elastic properties to variations of petrophysical properties.
- Apply fluid-substitution techniques to various lithologies to evaluate seismic discrimination of pore-fluid properties.
- Quantify components of AVO inversion to variations in pore compressibility, lithology, porosity, thickness, and recognize limitations of ray-theory equations for each AVO class.
- Quantitatively calibrate borehole properties to both boundary (reflectivity) and layer (impedance) attributes and determine appropriate attributes for lithology and pore-fluid discrimination.
- Compare and contrast seismic signatures for Class 1, 2, 3, and 4 AVO anomalies and the interpretation sensitivity associated with each AVO Class.