Analysis of Natural Fractures and Borehole Ellipticity Travis Peak Formation East Texas

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This report summarizes petrographic studies of natural and coring-induced fractures in 7 cores from the Travis Peak Formation, a low-permeability gas sandstone in East Texas, and also presents an analysis of fracturing and wellbore elongation based on Borehole Televiewer, Formation Microscanner, and Ellipticity logs from 12 Travis Peak wells.

Natural, vertical extension fractures in sandstone are open or only partly mineral-filled in the cored depth range (approximately -5,000 to -10,000 ft), and they are therefore potential gas reservoirs as well as a potentially important influence on commercial hydraulic fracture treatment. Crack-seal structure in fracture-filling quartz shows that fracturing and quartz cementation were contemporary; this result, together with evidence of timing of fracturing and the large water volumes that are inferred to have passed through the Travis Peak, suggests that natural hydraulic fracturing influenced fracture development.

Healed transgranular microfractures that occur in sandstone can be used to ascertain natural fracture trends in core that lacks macrofractures, and coring-induced petal-centerline fractures can be used to infer stress orientations. Fractures trend ENE to E. In the upper Travis Peak, borehole ellipticity trends ENE, parallel to fracture trends, and in the lower Travis Peak ellipticity trends NNW, parallel to the direction of least horizontal stress.


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