Advance Seismic Petrophysics

Introduction:

Seismic petrophysics entails the deliberate and meticulous utilization of rock physics data and theory in conjunction with well-log data to interpret seismic observations. This course commences with the introduction of commonly employed and straightforward models, gradually progressing to more intricate and realistic interpretations. Throughout the course, the interrelationships between laboratory experiments, theoretical concepts, well-logs, and seismic data are thoroughly explored. Participants will have access to a set of spreadsheets that incorporate various models, enabling predictions of fluid properties, rock properties, and seismic response (including AVO and elastic impedance). In-class exercises will involve both simple calculations and the utilization of these spreadsheets. The course covers a range of rock types, including unconsolidated and consolidated clastics, carbonates with vugs and fractures, shales, and formations with heavy oil. Real-world examples from diverse locations around the globe will be examined.

Course Objectives:

At the conclusion of the course, students should be able to understand the application of rock physics models and theory, to combine those with well-log information in a petrophysical evaluation, and to employ the results in modeling and interpretation of seismic data.

Who Should Attend?

This course is intended to be taken by geoscientists and engineers with some experience in at least one of the following: petrophysics, seismic interpretation, seismic processing, reservoir characterization, or reservoir engineering. It is not expected that any participants will have experience in more than one of those fields, but this course will allow the participants with expertise in one field to understand the relationships of petrophysical data and seismic interpretation for reservoir characterization, and to communicate with others in any of those fields.

Course Outlines:

Fundamentals

• Common soft-rock problems? Porosity determination? Fluid determination? Rules of thumb? Litho logy; effect of shale
• Invasion profiles, moveable hydrocarbons? Depth of investigation for different logging tools? How much hydrocarbon actually moves?
• Fluid substitution? Empirical from Brie’s model for logging data
• Mixing laws for rocks and fluids? Upper, Lower, Patchy, Brie’s? Some theory: Hashin-Shtrikman, Kuster-Toksoz
• Gassmann’s model (and Biot’s) for fluid substitution
• Log data (including dipole logs)? Obtaining input parameters for use in fluid substitution? Matching water and oil/gas legs in a well
• Fluid substitution in absence of Vs? P-wave modulus approach? Xu and White model for realistic rocks
• Vernik’s observations
• Kachanov’s model

Seismic Attributes

• Popular post-stack seismic attributes? Point-based attributes: amplitude, etc? Hilbert transform attributes: Envelope, Phase, and Frequency? Interval attributes: Velocity, RMSAmp, etc? Inversion, Velocity analysis? Structural attributes: Coherence, Dip, Azimuth
• The relationships of these attributes to rock properties? What is commonly assumed? What may often be the case instead
• Realistic rocks and their properties? Classics? Digenesis (Mechanical, Chemical) effects? Carbonates? Shale? Fluids in these rocks? Pressures on these rocks
• Popular pre-stack seismic attributes? Principles of AVO? Classifications of AVO behavior? Approximations to Zoeppritz equations
• Three term ones
• Two-term ones, including Shuey? The Fluid Factor? Lamda-rho and mu-rho? Elastic impedance
• Relationships of these attributes to rock properties? Conventional bright spots and Class III AVO? Pitfalls? Fluids versus litho logy (shaliness or porosity)

Fluids and Complicated Rocks

• Fluid properties: oil, gas, and water? GOR, API, etc? Batzle and Wang approach? Limitations? Mixture models (Gassmann, patchy, etc)
• Common hard-rock problems (carbonates, tight sands)? Sensitivity to pore shape? How can we estimate sensitivity to fluids and/or litho logy?
• Rock physics treatment of vuggy or cracked rocks? Spherical porosity? Kuster-Toksoz (and others)? Brie’s models based on K-T? Anisotropy, aligned cracks or grains
• Thomsen parameters
• Log analysis problems in vuggy or cracked rocks? Porosity indicators? Cementation exponent, saturation? What is important for seismic
• Seismic examples from the literature? Velocity sags from fracturing? Velocity differences from pressures and saturations? Anisotropic observations
• Processing considerations

Advanced Petro physical and Seismic Techniques

• Shaly-sands and rock physics relationships? Clay? Views of rock physics in a ternary space? Shale definition? How to determine silt content? Log interpretation for shaly sands? Marion’s observations? Skelt’s observations, boomerang models? Diagenesis revisited
• Inversion (acoustic and elastic)? Acoustic impedance
• Bandwidth considerations
• Methods of inversion? Elastic impedance
• Partial stacks
• Two or three or four offset ranges
• Rephrasing in terms of other parameters
• Reliability
• Example: Teal South gathers, Acae impedance volumes
• Scaling effects (size matters)? Layering
• Thin-bed effects
• Backus averaging, effective medium theories
• Example: Wyoming logs with coal beds
• Anisotropy (VTI)
• Effects on seismic gathers
• Modified NMO velocities – more terms
• Attenuation (and how it is improperly credited with certain affects)