Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Dvorkin, J. Articles by Derzhi, N. Search for Related Content GeoRef GeoRef Citation

Lithology substitution in fluvial sand

Stanford University, California, U.S. and Rock Solid Images, Texas, U.S.

Joel Walls, Richard Uden, Matt Carr, Maggie Smith and Naum Derzhi

Rock Solid Images, Texas, U.S.

Corresponding author: jack@pangea.stanford.edu

The first 20% of the full text of this article appears below.

Dichotomy in geophysical remote sensing is both relative and absolute: while the seismic reflection relates to the impedance contrast, the reservoir properties, such as porosity, relate to the absolute value of the impedance. One way of interpreting the relative in terms of the absolute is to perturb the absolute and calculate the corresponding relative. To accomplish this task in geophysics, the velocity and density curves from an existing prototype well are perturbed according to a likely situation at a different location. A new pseudowell thus created is used to generate synthetic full-waveform seismograms which are then compared to real data at the location, with the expectation that the similarity in the seismic response reflects the similarity in the reservoir properties.

To create a pseudowell from a prototype, a model is required that would quantify the relation between the changes in reservoir properties and conditions on the one hand and the changes in velocity and density on the other hand. One of the most commonly used such models is fluid substitution where the Gassmann or V_p-only equations are employed to predict the elastic changes due to the changes in the original reservoir fluid.

The situation becomes more challenging when one needs to perturb the matrix and frame of the rock, i.e., conduct lithology substitution. In this case, a transform from mineralogy, texture, and porosity to the elastic properties is needed. Unfortunately for the modeler and interpreter, more than one of such transforms may exist in sediment.

Consider, for example, Figure 1 where the sonic P-wave impedance is plotted versus the total porosity for clean sand intervals in five different wells. The data in the low-to-medium porosity range form a trend that can be matched by the Raymer et al. model. This model, however, fails to describe the trend formed . . . [Full Text of this Article]