Time-Dependent Failure Analysis of Inclined Boreholes in Fluid-Saturated Formations

1999 ◽  
Vol 121 (1) ◽  
pp. 31-39 ◽  
Author(s):  
L. Cui ◽  
Y. Abousleiman ◽  
A. H-D. Cheng ◽  
J.-C. Roegiers
Keyword(s):  
Time Dependent ◽  
Far Field ◽  
Borehole Stability ◽  
Dependent Failures ◽  
Principal Axes ◽  
Saturated Formations ◽  
Inclined Boreholes ◽  
Mud Pressure ◽  
Dependent Failure ◽  
Far Field Stress

This paper presents time-dependent poroelastic failure analyses of boreholes drilled in directions inclined to the far-field stress principal axes in fluid-saturated isotropic porous formations. The work is based on a recently derived analytical solution. The analyses include collapse as well as fracturing failures. The time-dependent failures in relation to borehole inclination, azimuth, and mud pressure are presented. The critical roles of poroelastic constants in borehole stability are also demonstrated.

A Semianalytical Poroelastic Solution To Evaluate the Stability of a Borehole Drilled Through a Porous Medium Saturated with Two Immiscible Fluids

SPE Journal ◽  
2020 ◽  
Vol 25 (05) ◽  
pp. 2319-2340
Author(s):  
Jiajia Gao ◽  
Hon Chung Lau ◽  
Jin Sun
Keyword(s):  
Porous Medium ◽  
Pore Pressure ◽  
Immiscible Fluids ◽  
Time Dependent ◽  
Excess Pore Pressure ◽  
Porous Rock ◽  
Borehole Stability ◽  
Mud Pressure ◽  
The Impact ◽  
Fluid Phases

Summary Conventional drilling design assumes that the porous rock is fully saturated with a single fluid and therefore tends to inaccurately predict the mud weight needed for borehole stability because the pore space of the porous rock may actually have two or more fluids. This paper provides a new semianalytical poroelastic solution for the case of an inclined borehole subjected to nonhydrostatic stresses in a porous medium saturated with two immiscible fluids: water and gas. The new solution is obtained under plane-strain condition. The wellbore loading is decomposed into axisymmetric and deviatoric cases. The time-dependent field variables are obtained by performing the inversion of the Laplace transforms. On the basis of the expansion of the Laplace-transform solution, we derive the unsaturated poroelastic asymptotic solutions for early times and for a small radial distance from an inclined wellbore. Sensitivity analyses are performed on different ratios of bulk modulus of two fluid phases to pore pressures of the unsaturated case. In addition, the comparative analyses of pore-pressure differences are made between the unsaturated and saturated cases. The impact of the unsaturated poroelastic effect on pore pressure, stresses, and borehole stability is investigated. Our results show that the excess pore pressure caused by the poroelastic effect is generally higher for the saturated case (water) than the unsaturated case because of the large difference between the compressibility of fluid phases (water and gas). The time dependency of the poroelastic effect causes the safe-mud-pressure window of both the unsaturated and saturated cases to narrow and approach the long-time poroelastic one with increasing time. The safe-mud-pressure window narrows with increasing initial gas saturation. Contrary to the unsaturated case, the saturated case that assumes the formation to be saturated by one fluid (e.g., water) tends to optimistically predict a wider safe-mud-pressure window required for borehole stability. This new semianalytical poroelastic solution enables the drilling engineer to more accurately estimate the time-dependent stresses and the pore pressure around a borehole, thus allowing a mud weight design that will ensure borehole stability.

New strength metrics for containerboards: influences of basic papermaking factors

2018 ◽  
Vol 33 (4) ◽  
pp. 592-602
Author(s):  
Amanda Mattsson ◽  
Tetsu Uesaka
Keyword(s):  
Time Dependent ◽  
New Method ◽  
Creep Tests ◽  
Material Parameters ◽  
Dependent Failures ◽  
Short Term Strength ◽  
New Material ◽  
End Use ◽  
Future Work ◽  
Operating Window

Abstract In end-use, containerboard is subjected to a variety of loading histories, such as seconds of loading/unloading, hours of vibration, days of creep load. The fundamental question is whether the commonly measured static strength represents “strength” under these conditions. Another question is, since those time-dependent failures are notoriously variable, how to describe the probabilistic aspect. This study concerns the characterisation of these different facets of “strength”. In our earlier work, we have investigated the theoretical framework for time-dependent, probabilistic failures, and identified three material parameters: (1) characteristic strength, {S_{c}}, representing short-term strength, (2) brittleness/durability parameter, ρ, and (3) reliability parameter, β. We have also developed a new method that allows us to determine all these parameters much faster than typical creep tests. Using the new method, we have started investigating effects of basic papermaking variables on the new material parameters. Among the samples tested, the parameter ρ varied from 20 to 50, and β from 0.5 to 1.0. This suggests that, even within the current papermaking practice, there is a wide operating window to tune these new material parameters. The future work is, therefore, to find specific manufacturing variables that can systematically change these new material parameters.

Experimental Study of Time-dependent Failure of High Strain Composites

2020 ◽  
Author(s):  
Kanthasamy Ubamanyu ◽  
Daniele Ghedalia ◽  
Armanj D. Hasanyan ◽  
Sergio Pellegrino
Keyword(s):  
Experimental Study ◽  
High Strain ◽  
Time Dependent ◽  
Dependent Failure

The Integrative Time-Dependent Modeling of the Reliability and Failure of the Causes of Drivers' Error Leading to Road Accidents

2015 ◽  
pp. 1279-1294
Author(s):  
Khashayar Hojjati-Emami ◽  
Balbir S. Dhillon ◽  
Kouroush Jenab
Keyword(s):  
Human Error ◽  
Time Dependent ◽  
Failure Rates ◽  
Road Accidents ◽  
Road Transportation ◽  
The Road ◽  
Representational Model ◽  
On The Road ◽  
The Moment ◽  
Dependent Failure

Nowadays, the human error is usually identified as the conclusive cause of investigations in road accidents. The human although is the person in control of vehicle until the moment of crash but it has to be understood that the human is under continued impact by various factors including road environment, vehicle and human's state, abilities and conduct. The current advances in design of vehicle and roads have been intended to provide drivers with extra comfort with less physical and mental efforts, whereas the fatigue imposed on driver is just being transformed from over-load fatigue to under-load fatigue and boredom. A representational model to illustrate the relationships between design and condition of vehicle and road as well as driver's condition and state on fatigue and the human error leading to accidents has been developed. Thereafter, the stochastic mathematical models based on time-dependent failure rates were developed to make prediction on the road transportation reliability and failure probabilities due to each cause (vehicle, road environment, human due to fatigue, and human due to non fatigue factors). Furthermore, the supportive assessment methodology and models to assess and predict the failure rates of driver due to each category of causes were developed and proposed.

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