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Modified cam-clay model for large stress ranges and its predictions for geological and drilling processes

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doi: 10.1029/2020JB019500
Authors:Heidari, Mahdi; Nikolinakou, Maria A.; Flemings, Peter B.
Author Affiliations:Primary:
University of Texas at Austin, Bureau of Economic Geology, Jackson School of Geosciences, Austin, TX, United States
Volume Title:Journal of Geophysical Research: Solid Earth
Source:Journal of Geophysical Research: Solid Earth, 125(12). Publisher: Wiley-Blackwell for American Geophysical Union, Washington, DC, United States. ISSN: 2169-9313
Publication Date:2020
Note:In English. 79 refs.; illus., incl. sects., 4 tables
Summary:We modify the Modified Cam-Clay (MCC) model for large stress ranges encountered in geological applications. The MCC model assumes that the friction angle (??span type="mathematics"??Φ??/span??) and the slope of the compression curve (??span type="mathematics"??λ??/span??) of a mudrock are constant and thus predicts constant values for the lateral effective stress ratio under uniaxial, vertical strain (K0) and undrained strength ratio ( ??math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="urn:x-wiley:21699313:media:jgrb54562:jgrb54562-math-0001" wiley:location="equation/jgrb54562-math-0001.png"????mfrac????mrow????msub????mi??S??/mi????mi??u??/mi????/msub????/mrow????mrow????mi??σ??/mi????msub????mo??'??/mo????mi??v??/mi????/msub????/mrow????/mfrac????/math??). However, experimental work shows that ??span type="mathematics"??λ??/span??, ??span type="mathematics"??Φ??/span??, and ??math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="urn:x-wiley:21699313:media:jgrb54562:jgrb54562-math-0002" wiley:location="equation/jgrb54562-math-0002.png"????mfrac????mrow????msub????mi??S??/mi????mi??u??/mi????/msub????/mrow????mrow????mi??σ??/mi????msub????mo??'??/mo????mi??v??/mi????/msub????/mrow????/mfrac????/math?? decrease and K0 increases substantially with stress over large stress ranges (e.g., up to 100 MPa). We incorporate the stress dependency of ??span type="mathematics"??λ??/span?? and ??span type="mathematics"??Φ??/span?? into the MCC model and use the new model to predict ??math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="urn:x-wiley:21699313:media:jgrb54562:jgrb54562-math-0003" wiley:location="equation/jgrb54562-math-0003.png"????mfrac????mrow????msub????mi??S??/mi????mi??u??/mi????/msub????/mrow????mrow????mi??σ??/mi????msub????mo??'??/mo????mi??v??/mi????/msub????/mrow????/mfrac????/math?? and K0 ratios. The modified model, with only one additional parameter, successfully predicts the stress dependency of these ratios. We encode the modified model and use it for finite-element analysis of a salt basin in the deepwater Gulf of Mexico. The stresses that the new model predicts around salt differ significantly from those predicted using the original model. We incorporate the stress dependency of the friction angle into the analytical models developed for critical tapers, wellbore drilling, and the stability of submarine channel levees. We show that the decrease of the friction angle with stress (1) results in a concave surface for critical wedges, (2) shifts the drilling window to higher mud weights and makes it narrower for a vertical wellbore, and (3) causes deep-seated failure of submarine channel levees at lower angles. Our study could improve in situ stress and pore pressure estimation, wellbore drilling, and quantitative understanding of geological processes. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.
Subjects:Boreholes; Bulk modulus; Clastic rocks; Clastic sediments; Clay; Compression; Crust; Decollement; Deep-sea environment; Density; Deposition; Drilling; Elastic constants; Elastic properties; Failures; Friction; Friction angles; Hydrocarbons; Hydrostatic pressure; Levees; Marine environment; Models; Mudstone; Organic compounds; Petroleum; Plasticity; Poisson's ratio; Pore pressure; Prediction; Reservoir rocks; Salt domes; Sedimentary rocks; Sediments; Shear modulus; Slopes; Stability; Strain; Strength; Stress; Stress fields; Submarine environment; Subsidence; Topography; Triaxial tests; Two-dimensional models; Uniaxial tests; Atlantic Ocean; Eugene Island; Gulf of Mexico; North Atlantic; Sigsbee Escarpment; Mad Dog Field
Coordinates:N180000 N300400 W0803000 W0980000
Record ID:897674-38
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom
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