Report Summary

Abstract

This report contains the results of work completed during the twelfth year of the Borehole Acoustics and Logging Consortium in the Earth Resources Laboratory at M.LT. This year we have achieved one of our major goals in numerical modelling. We have completed a code for modelling elastic wave propagation in a borehole in a generally anisotropic and heterogeneous formation in three dimensions. This opens up a lot of possibilities in terms of modelling full waveform and shear wave logging. Along the same trend, we have continued to develop our numerical modelling of permeable zones. We are able to simulate Stoneley wave propagation in zones with varying vertical permeability. This allows us to match the field observations better. Another application of numerical flow modelling is to model tracer transport in heterogeneous media. This has applications in environmental as well as enhanced oil recovery areas. Another area we have addressed is the influence of borehole geometry on the full waveform and dipole wavefield. We have looked at the effects of a borehole with an irregular cross-section on the full waveform, and we have also effectively modelled a borehole with a vertically varying radius, such as in the case of washouts. We can model the scattered Stoneley waves from these washouts and the results compare well with data. On the field data Side, we have a paper dealing with the estimation of permeability from Stoneley waves. This case study was done in a water well. We have processed a number of other data sets during the past year, and some of the results will be discussed at the Annual Meeting. On the more theoretical side, we have a paper on the radiation of a borehole source into a layered or transversely isotropic medium. This work is done using the Boundary Element method. We also have a paper addressing the possibility of using non-linear semblance to better process the full waveform array data. The idea is to estimate velocity changes (increases) away from the borehole. In the laboratory we have examined the effects of fractures (vertical, horizontal, and inclined) on flexural wave propagation. We have also begun to investigate the electroseismic coupling in porous rocks, with an eye on the possibility of coupling acoustic and electric logs to better delineate permeability/fluid changes in the field. More detailed descriptions of the papers follow.