Reflectivity versus water saturation

Problems in Exploration Seismology and their Solutions

Series	Geophysical References Series
Title	Problems in Exploration Seismology and their Solutions
Author	Lloyd P. Geldart and Robert E. Sheriff
Chapter	5
Pages	141 - 180
DOI	http://dx.doi.org/10.1190/1.9781560801733
ISBN	ISBN 9781560801153
Store	SEG Online Store

Problem 5.8

What shale velocities are consistent with the Figure 5.8a oil-sand data?

Solution

We determine velocities and reflectivities for two values of water saturation for each of the three depths, neglecting differences between sand and shale densities. Setting $\rho _{ss}=\rho _{sh}$, equation (3.6a) becomes ${\begin{aligned}R=\left(V_{ss}-V_{sh}\right)/\left(V_{ss}+V_{sh}\right),\\V_{sh}=V_{ss}\left(1-R\right)/\left(1+R\right).\end{aligned}}$

Figure 5.8a.  Effect of water saturation on velocity (i) and reflectivity (ii) (after Domenico, 1974). Solid curves are for gaseous, dashed curves for liquid hydrocarbons.

Table 5.8a. Oil-sand data from Figure 5.8a.

Depth	Water saturation	$R$	$V_{ss}$	$V_{sh}$
610 m	30%	–0.08	1.7 km/s	2.0 km/s
	70	–0.03	1.8	1.9
1830	30	–0.10	2.3	2.8
	70	–0.07	2.4	2.8
3050	30	–0.10	2.7	3.3
	70	–0.07	2.8	3.2

From Figures 5.8a(i,ii) we obtain the data in Table 5.8a for oil sands. These are plotted as triangles on Figure 5.6a.

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Table of Contents (book)

Also in this chapter

• Maximum porosity versus depth
• Relation between lithology and seismic velocities
• Porosities, velocities, and densities of rocks
• Velocities in limestone and sandstone
• Dependence of velocity-depth curves on geology
• Effect of burial history on velocity
• Determining lithology from well-velocity surveys
• Reflectivity versus water saturation
• Effect of overpressure
• Effects of weathered layer (LVL) and permafrost
• Horizontal component of head waves
• Stacking velocity versus rms and average velocities
• Quick-look velocity analysis and effects of errors
• Well-velocity survey
• Interval velocities
• Finding velocity
• Effect of timing errors on stacking velocity, depth, and dip
• Estimating lithology from stacking velocity
• Velocity versus depth from sonobuoy data
• Influence of direction on velocity analyses
• Effect of time picks, NMO stretch, and datum choice on stacking velocity

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