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Introduction to

Rock Physicsby

Gary Mavko

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ContentsIntroduction 1Basic Geophysical Concepts 14Continuum Mechanics 26Porosity 71Conceptual Overview of Factors Impacting Velocities 73Effective Medium Models 113Shaley Sand; Velocity-Porosity Relations 164Sand Models 203Fluid Flow and Permeability 215Velocity Dispersion and Q 229Partial Saturation 261Patchy Flow Simulation 270Upscaling 288Vp/Vs - Rock Physics of AVO 302

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Courtesy Per Avseth

What Controls Amplitude over thisNorth Sea Turbidite?

Lithology, porosity, pore fluids, stresses… but also sedimentation and diagenesis

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From Nestvold, 1989

Image of Saturation and ReservoirHeterogeneity.Can we understand this quantitatively?

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Seismic Signatures of Pore Fluidsand Saturation Heterogeneity

Blangy, 1992

Oil and Gas

Water

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Buried Stream ChannelSand or Clay? Water or Oil?

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2

2.5

3

3.5

4

4.5

5

0 0.2 0.4 0.6 0.8 1

Vp (k

m/s

)

Sw (fraction)

Drainage

Imbibition

K.1

Seismic velocity depends onpore fluids … but not uniquely!

After Knight and Nolen-Hoeksema, 1990

It also depends on saturation scales.

Vp

(km

/s)

Sw (fraction)

Imbibition, Fine Scale

Drainage, Coarse Scale

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•Downscaled Saturations•Increasing Patchiness•Decreasing total gas thickness

4D Signature of saturation, dependson rock stiffness, fluids, porosity, …and saturation scale

Courtesy Madhumita Sengupta

Observedfrom fieldseismic

Prediction based onupscaled flow simulatorare poor

∆ RMS Amp (Near)

∆ R

MS

Am

p (M

id)

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Fractures have a variety of seismicsignatures, depending on lithology,fracture orientations, pore fluids

Gas: smallerazimuthal AVOthan water!

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Water-filled Fracturesin Cap Rock

Gas-filled Fracturesin Reservoir

Pitfall: Water saturated fractured capresembles gas-saturated fractured Res.

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Rock PhysicsDiscover, understand relationsbetween1. Seismic Attributes:•Velocity•Impedance•Reflectivity•AVO•Attenuation•Etc.

2. Rock and Fluid Properties:•Rock type, mineralogy•Porosity•Pore fluids, saturation•Stress, Pore, Pressure, Temperature

Why?•Quantify Seismic Interpretation•Understand the links between geology & seismic•Make smarter extrapolations•Quantify uncertainty

•Understand, Minimize Interpretation Risk

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Rock physics:• understand relations between geophysical

measurements and rock properties;• emphasis on interpreting seismic, sonic,

and ultrasonic data

Petrophysics:• interpretation of logs for formation

evaluation.• similar to rock physics, with emphasis on

well logs, and often ignoring sonic logs andseismic

Rock Mechanics:• Emphasis on stress, faulting, fracture

processes

People Often Ask the Difference:

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Goal of this course:

•Synthesize, generalize the currentstate of the art•Provide recipes, recommendations

•Point out pitfalls in the use of Rockphysics and shortcomings of ourknowledge

•Hopefully, to give you new tools touse back at the office