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Sequential Backus Averaging

Upscaling well logs to seismic wavelengths

Diamond Geoscience Research Corporation, Tulsa, Oklahoma, U.S.

Corresponding author: R. Lindsay, ROLindsay@dgrc.com

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

The measure of geologic knowledge spans a tremendously wide geometric scale. In the vertical dimension alone the range is from microscopic clay particle morphology and pore throat geometry to basinal megatrends many kilometers thick. Of a more limited scope, and inherent to building synthetic seismograms, is the process of relating logging-tool resolution measurements to seismic wavelengths—a tens- of-centimeters to tens-of-meters problem. This upscaling can be achieved by Sequential Backus Averaging.

In oil and gas exploration, 1-D synthetic seismograms are routinely generated from well logs. These synthetics correlate or tie well-bore-derived rock-property measurements to seismic trace data (Figure 1). Additionally, offset synthetics are used to understand how lithology and pore fluid properties are related to changes in AVO. The amplitude and AVO changes are caused by elastic rock-property contrasts (Figures 2 and 3). However, for these models to be reliable, the upscaling process must not distort the geologic morphology or geometry.

View larger version (54K): [in this window] [in a new window]   Figure 1. 1-D synthetic seismograms are used to tie well bore derived rock properties to seismic trace data.

View larger version (156K): [in this window] [in a new window]   Figure 2. Amplitude anomalies associated with elastic rock property contrasts. Warm colors represent high amplitudes (large rock-property contrasts).

View larger version (131K): [in this window] [in a new window]   Figure 3. AVO anomalies associated with elastic rock-property contrasts. Warm colors show increasing amplitudes. Cool colors represent decreasing amplitudes.