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The Effects of Lamination/Bedding on the Brittleness for the Woodford Shale Silica-Rich Intervals, From the Wyche-1 Core-Well Analysis, Pontotoc County, Oklahoma

Abstract

The Woodford Shale (WDS) as many other self-source unconventional rocks is evidently anisotropic. However, anisotropy (lamination/bedding) is not commonly included on defining “fracability”. FMI log, Core (Wyche-1) and thin section inspection illustrates that middle and lower WDS brittle intervals are characterized by more frequent and visible laminae, in comparison with the upper Woodford. Thomsen' coefficients ε and γ, obtained from Ultra Pulse Velocities (UPV) analysis, were used to quantify anisotropy and to explore their potential effects on rock “fracability”. The intervals that exhibit more laminae (anisotropy) are characterized by higher ε and γ coefficients, which are also characterized by less Fracture toughness (Kic) and Tensile Strength (T). Fracture Toughness (KIc) is a property which describes the ability of a material containing a crack, to resist fracture. It is one of the most important properties for hydraulic fracturing designs and is a measurement of the energy required to grow a thin crack expressed on MPa m1/2 or MN/m1/2. Tensile Strength (T) is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. T is defined as a stress, which is measured as force per unit area (Pa or N/m2) The upper Woodford samples which were characterized by more diffuse and/or less laminae on thin sections and microresistivity logs are also represented by lower values at ε and γ anisotropic coefficients This work also illustrates that more laminae at middle Woodford brittle intervals creates more anisotropy planes of weakness, that may assist in reducing the effective minimum horizontal principal stress and they may response much brittle during hydraulic stimulation.