Improved characterization of anisotropic elastic moduli and stress for unconventional reservoirs using laboratory mineralogy, toc, static, and dynamic geomechanical data

Farrukh Hamza, Ming Gu, John Quirein, Cheng Chen, Vladimir Martysevich, Luis Matzar

Research output: Contribution to conferencePaperpeer-review

12 Scopus citations

Abstract

To fully characterize geomechanical properties of a vertically transverse isotropic (VTI) medium, such as shale, five independent stiffness coefficients are required. However, only three can be measured through sonic log measurements. This gap has traditionally been filled by applying the ANNIE model. One of the critical assumptions in the ANNIE model causes vertical Poisson's ratio to always be greater than horizontal Poisson's ratio and predicts the anisotropic and isotropic stresses to be equal. However, these assumptions are usually not the case in unconventional reservoirs. A modified-ANNIE (M-ANNIE 1) model helps overcome the limitations of the ANNIE by introducing two empirical multipliers. However, both the ANNIE and M-ANNIE 1 models require Stoneley wave velocity as input, which prevents their applicability in cased-hole conditions or conditions with no advanced sonic logging tools. Recently, two new methods, velocity regression (V-reg) model and a further modified ANNIE model (M-ANNIE 2), were proposed to predict the stiffness coefficients independent of the Stoneley wave. It is observed that the simple generic relationships derived from core ultrasonic data are not sufficient for stiffness coefficients characterization. Ultrasonic velocities were measured on whole cores from a North American shale play in 0, 45, and 90° orientations to obtain direction-dependent compressional (Vp) and shear waves (Vs) velocities. Different anisotropic acoustic models were applied to compare their prediction capacity and limits. This study includes more laboratory data, such as X-ray diffraction (XRD) mineralogy and total organic carbon (TOC), to provide a lithological context. It was observed the shale has a large portion of carbonate (> 80v%), and its acoustic anisotropy indicator Thomsen parameters, epsilon and gamma, are strongly related to clay and kerogen content. This paper discusses how the high carbonate content alters the previously established generic models for M-ANNIE 1, 2, and V-reg. The paper also investigates the relationship between the dynamic and static elastic moduli interpreted from the ultrasonic and triaxial data, respectively. The dynamic and static data were used to fit widely used dynamic-to-static conversion equations: the Canady and Morales equations. The Canady equation was extended to the “very hard” (greater than 70 GPa Young’s modulus) regime, while the Morales equation was extended to the regime of less than 10% porosity. Next, the calibrated dynamic Young’s modulus is also used to estimate the unconfined compressive strength (UCS). The prediction qualities of different acoustic anisotropic models are investigated. As compared with the conventional ANNIE and isotropic models, the lithology-based anisotropic acoustic models (M-ANNIE 1, 2, and V-reg) highly improve the predictions of the stiffness coefficients and elastic moduli; hence, they provide better predictions of the minimum horizontal stress. Accurate predictions of elastic moduli and stress are crucial for selecting proper drilling mud, cement weights, and drilling/perforation locations.

Original languageEnglish
Pages1-18
Number of pages18
StatePublished - 2016
EventSPWLA 57th Annual Logging Symposium 2016 - Reykjavik, Iceland
Duration: 25 Jun 201629 Jun 2016

Conference

ConferenceSPWLA 57th Annual Logging Symposium 2016
Country/TerritoryIceland
CityReykjavik
Period25/06/1629/06/16

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