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Analysis of Rock Mechanical Properties by Mineralogy and Their Potential Effects from Hydraulic Fracturing in the Woodford Shale

Aoudia, Khodir 1; Miskimins, Jennifer 1; Mnich, Cheryl 2; Harris, Nicholas B.2
1 Petroleum Engineering, Colorado School of Mines, Golden, CO.
2 Geology and Geological Engineering, Colorado School of Mines, Golden, CO.

Shale reservoirs are commonly considered to be fine-grained, low permeability rocks with high clay content and little inherent heterogeneity. However, as more shale plays are developed, it is evident that shale reservoirs vary considerably in their mineralogical and chemical properties and that this variability has consequences for physical properties. Since shale reservoirs are commonly subjected to hydraulic fracturing treatments, investigating the relationship between the mineralogy and physical / mechanical properties of these reservoirs is crucial.

This poster describes a study of the Woodford shale, Permian Basin, west Texas. The outcome of a hydraulic fracturing treatment on a Woodford well suggests systematic differences in mechanical properties between the upper and lower Woodford. While the upper, more quartz-rich, section responded positively to fracturing, the lower, less-quartz-rich, zone did not show any improvement. This raised the need for an investigation of the formation’s response to fracturing and the relationship between mineralogy and mechanical properties in the Woodford shale.

The study is performed using gamma ray, photoelectric, resistivity, density and neutron well logs and a core of approximately 360 ft for lab measurements. Based on the mineralogical variation (mainly quartz and clay content), the formation is divided into 3 distinct sections and 39 different sub-sections. In terms of mechanical properties, the formation can be divided into two distinctive parts, based on lab measurements, correlated with the well log data. The upper part of the formation, as defined by mechanical properties, is characterized by an average Young’s modulus and Poisson’s ratio of 1.7 107 psi and 0.15 respectively; this interval has a high quartz content. The lower part of the formation, which contains significantly less quartz, has an average Young’s modulus of 1.35 107 psi and Poisson’s ratio in the range of 0.14. Since a brittle rock is characterized by a high Young’s modulus and a low Poisson’s ratio, the results of the hydraulic fracturing treatment are clearly consistent with the mechanical properties, such that the better hydraulic fracturing occurred in rock with a 26% higher Young’s modulus. Variations of clay content, from about 18% to about 32%, have little influence on the mechanical properties. This poster discusses these results and their implications in hydraulic fracturing completions.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009