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Rock Mechanical Properties and Borehole Stability of Gas Shale

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Category: Mining

Last Updated on 16 July 2014

Published on 21 March 2014

Hits: 3865

Authors:

Chuanliang Yan, Jingen Deng, Baohua Yu, Wenliang Li, Lianbo Hu

State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing, China

Abstract:

Serious borehole instability occurs frequently during drilling in shale gas reservoirs. Shale gas reservoirs are featured by tight matrix, well-developed micro-fissures and laminations, and their peculiar mechanical properties are different from those of ordinary tight sandstones or carbonates. Thus, implementing correlative studies is of great significance to drilling and subsequent reservoir stimulation. Rock mechanical tests are performed to gas shale from south of China by the MTS-816 Rock Test System. The variation of rock mechanical properties with the angle between axial stress and the bedding plane normal (coring angle) is analyzed by the laboratory tests and a failure criterion is verified and applied to determine the strength of gas shale. The shale strength decreases first and then increases with the increasing of coring angle. It gets the maximum value with the coring angle of 0° and gets the minimum value with the coring angle of about 60°. The Young’s modulus and Poisson’s ratio increase with the increase of coring angle. Besides, the borehole stability model of shale gas well is established by combining transverse isotropic constitutive model and the continuously variable cohesion strength criterion. The collapse pressure is lowest when drilling to the maximum horizontal stress direction and reaches its maximum when drilling to the minimum horizontal stress direction.

References:

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