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Integrated Study of Shale Aniostropic Behavior : Fluid Flow, Ultrasonic and Mechanical Characteristics

Mehdi Mokhtari
Colorado School of Mines

Abstract

Experimental results of an integrated study on several US shale plays are presented in this paper. Among the tested samples, Eagle Ford is a mature calcite-rich, Green River is an immature dolomite-rich, Mancos is a low-TOC quartz-rich, Bakken is a high-TOC illite-rich, and Niobrara is a mature calcite-rich shale samples.

Mechanical and ultrasonic measurements are conducted simultaneously in a triaxial cell at different confining stresses. Eagle Ford samples with fractures parallel to bedding have lower Young's modulus and Poisson's ratio at low axial stress. However, the fractures are gradually closed with increase of axial stress which makes Young's modulus and Poisson's ratio similar to the intact samples. This trend is also supported by compressional and shear velocity measurements. All the samples show significant anisotropy in compressive strength, Young's modulus, and compressional velocity, with horizontal samples having highest values. Shear sliding failure mechanism was observed on 60-degree Mancos shale while step-wise failure was observed in vertical and horizontal samples. Post-failure compressional velocity is compared with before failure values. Dynamic to static correlation and comparison to logs are discussed.

Layering anisotropy causes higher permeability in horizontal samples with respect to vertical and 45-degree samples. Moreover, several orders of higher permeability were measured in one of the samples having fracture detected by CT scan. Wettability was measured by contact angle method. Samples with higher TOC or maturity show higher oil wettability (higher contact angle with water).

The implication of these results on fracture mechanics, field data measurement and monitoring are discussed.

AAPG Search and Discovery Article #90202 © AAPG/STGS Geoscience Technology Workshop, Eagle Ford plus Adjacent Plays and Extensions Workshop, February 24-26, 2014, San Antonio, Texas