The objectives of this study were to reveal the existence of microfractures in tight gas sands and to investigate their effects on directional permeability. The knowledge of the orientation of microfractures and their impact on directional permeability could influence various reservoir engineering applications involved in developing tight gas sands. This study has been accomplished by analyzing and comparing the results of directional permeability measurements to acoustic velocity anisotropy and pétrographie analyses.

Both natural and stress relaxation (induced) microfractures were observed in all three tight gas formations analyzed: Cotton Valley, Travis Peak and the Frontier Formations. This study indicates that compressional velocity measurements and thin section analyses should be integrated to define the orientation of the microfractures. Induced microfractures appear to close under confining stress and consequently, permeability anisotropy measured at in-situ pressure has been interpreted to not be influenced by induced microfractures. The influence of natural microfractures on permeability anisotropy in tight gas sands was observed to be dependent on the degree and type of cementation and the pore network.

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