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WAVO & SHALEIND
WAVO is a new AVO technique developed by myself based in the very well known Intercept-Gradient method. The technique has a different approach in computing deviations and also takes into account weighting of these deviations. The standard Intercept-Gradient method is mainly based in shale background. WAVO methodology takes into account some deviations from Near, Far and Gradient data. The input to the algorithm should be horizon amplitudes (option to add time) in ASCII format. So, the user must feed horizon Near and Far amplitudes and optionally time of correlate horizon. The horizons should be reflections from low impeadance layers or negative amplitudes. The amplitudes can't be window averaged: they must be maximum negative amplitudes that matches a very well defined geological/seismic interface. Depending upon interpretation package, user must be very carefully when picking these amplitudes: he must be confident that far and near amplitudes came from the same interface. If using automatic picking based in a previous horizon, user must check the accuracy of these pickings. Far and near from different interfaces do not make any sense to AVO and implies error.
Wavo is very successful in its prediction, more then 90% drill proven. Also it indicates situations opened to be investigated by Shaleind, a tool described below, mainly in cases where a non reservoir horizon starts to be configured.
Also it is important to mention that WAVO values have similarity with standard deviation, in many cases indicating water, small netpay, oil/water contact or big netpay. From the WAVO maps and graphs it is also possible to interpret the presence of light oil or gas: I have examples from West África and Ofshore Brazil.
Next You may inspect a figure that is a WAVO map of a target horizon. This target were drilled and the drill was successful. UTM coordinates in all figures in this site are not the original ones.
SHALEIND was the first name given to a new tool developed to help in AVO studies. The idea was to indicate the target horizon as shales. By the time, we saw the evidence that in reality it was powerful to indicate not only shales but non reservoirs at all. Shaleind name was maintained, but the user must have in mind it is a non reservoir indicator tool.
The technique is similar to WAVO, operating in the reverse side: it is efficient as a non DHI indicator. The use of WAVO and Shaleind constitute a very powerfull combination, with dozens of good results indicating the presence of HC or the absence of reservoirs. Next figure shows a Shaleind map: more colored the map is, more non reservoir indication. More dark the color is, more indication of reservoirs or low porosity rocks.