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Wavelet Transformation as a Reservoir Characterization Tool in Shale Plays


The shale plays are the current industry boom around the world to enhance fossil fuel production. Several such plays have been identified in the United States and are being actively exploited. Previously, shales were considered as source rocks only due to their apparent homogeneous lithology. Subsequent researches have revealed that shales are not homogeneous and consist of coarser particles like sand and silt along with the clay-sized grains. It is the presence of these coarse grained particles that have made the previously perceived source rock to be produced like a reservoir.

Understanding lithological architecture of shales is important for optimum well placement and fracturing jobs. Visual log analysis does not help when it comes to identifying thin siltstone and sandstone layers within massive shales. This problem can be resolved by continuous wavelet transformations on openhole wireline logs like gamma ray, resistivity, neutron porosity, and velocity logs. This technique identifies the boundary between shaly and non-shaly formations and can pin down the precise depth at which this boundary exists.

Well logs are signals that can be transformed into a number of wavelets of various stretching, shifting, and magnitude. When added together, these wavelets reconstruct the original signal. Knowing how much the wavelet was stretched and shifted to match the signal tells us the location and frequency of the pulse.

Guas 1, Guas 3, Morelet, and Symlet 2 wavelets will be used for delineating the thin sandstone/siltstone layers in the wells with massive shale sections. Available production data can help validate the results of the wavelet transformation. This technique will help pin down the precise depths to the top of the reservoir interval as well as give a better picture about the extent of the reservoir, both of which are pertinent information for future well placements and hydraulic fracturing jobs.