The Bureau of Economic Geology The University of Texas at Austin Jackson School of Geosciences
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From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
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Bureau Seminar, February 14, 2014

Predicting the Stiffness Tensor of a Transversely Isotropic Medium: an Extension of the ANNIE model

Link to streaming video: available 02.14.2014 at 8:55am

John Quirein
Halliburton Technology Fellow, Petrophysics

Abstract:
It is well known that organic shale reservoirs have very low permeability. Any stimulated fracture system is influenced by extensive horizontal laminations that are pervasive in shale reservoirs. The laminations will strongly influence the hydraulic fracture height because of the difference in measured and predicted rock mechanical properties normal and parallel to the bedding planes. To accurately predict fracturing height and even fracture width from logs in this environment, these mechanical property differences must be taken into account. These predictions are typically derived by density/sonic measurements used in conjunction with the ANNIE equations (Schoenberg et al., 1996). Review of the publications using ANNIE model (Higgins et al. 2008; Waters et al. 2011) reveals that ANNIE always predicts v_vert ≥ v_horz. We show this to be the case in general for ANNIE. There are organic shales in which the horizontal over vertical Poisson's ratio (v_horz/v_vert) has been observed to range from 2 to 3. It is impossible to model these shales with the ANNIE equation. We present an extension of ANNIE which handles both cases, i.e., the vertical Poisson's ratio less than or greater than the horizontal Poisson's ratio. The new approach is shown to fit the core dynamic data and results in improved predictions of stress-induced phenomena such as fracture closure pressure and fracture width from well log data. Finally, the model is applied to appropriate field data from which the core measurements of the elastic moduli were obtained. The resulting predictions can be used to high-grade the selections of intervals to be perforated and fractured.

About the presenter:
John Quirein is a Halliburton Technology Fellow, Petrophysics, focusing in interpretation and software development with a recent emphasis on Gas Shale Petrophysics, geochemical log interpretation, geomechanics and multi-mineral solvers. He received a PhD from the University of Houston, and then worked 10 years for Schlumberger, 12 years for Mobil and the last 14 years for Halliburton. He is a past SPWLA President and past SPWLA Foundation president.

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