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Crack Faces (crack + face)

Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

Processing, modelling and predicting time-lapse effects of overpressured fluid-injection in a fractured reservoir

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2002
Erika Angerer
Summary Time-lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs. We analyse two 4-D, 3C onshore surveys from Vacuum Field, New Mexico, USA, where the reservoir of interest is a fractured dolomite. In Phase VI, a time-lapse survey was acquired before and after a pilot tertiary-recovery programme of overpressured CO2 injection, which altered the fluid composition and the pore-fluid pressure. Phase VII was a similar time-lapse survey in the same location but with a different lower-pressure injection regime. Applying a processing sequence to the Phase VI data preserving normal-incidence shear-wave anisotropy (time-delays and polarization) and maximizing repeatability, interval-time analysis of the reservoir interval shows a significant 10 per cent change in shear-wave velocity anisotropy and 3 per cent decrease in the P -wave interval velocities. A 1-D model incorporating both saturation and pressure changes is matched to the data. The saturation changes have little effect on the seismic velocities. There are two main causes of the time-lapse changes. Any change in pore-fluid pressures modifies crack aspect ratios. Additionally, when there are overpressures, as there are in Phase VI, there is a 90° change in maximum impedance directions, and the leading faster split shear wave, instead of being parallel to the crack face as it is for low pore-fluid pressures, becomes orthogonal to the crack face. The anisotropic poro-elasticity (APE) model of the evolution of microcracked rock, calculates the evolution of cracked rock to changing conditions. APE modelling shows that at high overburden pressures only nearly vertical cracks, to which normal incidence P waves are less sensitive than S waves, remain open as the pore-fluid pressure increases. APE modelling matches the observed time-lapse effects almost exactly demonstrating that shear-wave anisotropy is a highly sensitive diagnostic of pore-fluid pressure changes in fractured reservoirs. In this comparatively limited analysis, APE modelling of fluid-injection at known pressure correctly predicted the changes in seismic response, particularly the shear-wave splitting, induced by the high-pressure CO2 injection. In the Phase VII survey, APE modelling also successfully predicted the response to the lower-pressure injection using the same Phase VI model of the cracked reservoir. The underlying reason for this remarkable predictability of fluid-saturated reservoir rocks is the critical nature and high crack density of the fluid-saturated cracks and microcracks in the reservoir rock, which makes cracked reservoirs critical systems. [source]

Elastoplastic modelling of subsurface crack growth in rail/wheel contact problems

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2007
R. LUNDÉN
ABSTRACT Propagation of small subsurface cracks subjected to shear under repeated rolling contact load is studied. An analytical crack model (Dugdale) with plastic strips at the two crack tips is employed. Compressive stresses promoting crack closure and friction between crack faces are considered. The triaxial stress state is used in the yield criterion. A damage criterion is suggested based on experimental LCF data. In a numerical study, critical crack lengths are found below which propagation of an existing crack should be effectively suppressed. [source]

Study of crack growth in solid propellants

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2001
E. E. Gdoutos
The stress and displacement fields in an edge-cracked sheet specimen made of a solid propellant and subjected to a uniform displacement along its upper and lower faces was studied. The solid propellant was simulated as a hyperelastic material with constitutive behaviour described by the Ogden strain energy potential. A non-linear finite deformation analysis was performed based on the finite element code ABAQUS. A detailed analysis of the stress field in the vicinity of the crack tip was undertaken. The deformed profiles of the crack faces near the crack tip were determined. The results of stress analysis were coupled with the strain energy density theory to predict the crack growth behaviour including crack initiation, stable crack growth and final termination for two specimens with different dimensions. Crack growth resistance curves representing the variation of crack growth increment versus applied displacement were drawn. [source]

Delivery of Two-Part Self-Healing Chemistry via Microvascular Networks

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Kathleen S. Toohey
Abstract Multiple healing cycles of a single crack in a brittle polymer coating are achieved by microvascular delivery of a two-part, epoxy-based self-healing chemistry. Epoxy resin and amine-based curing agents are transported to the crack plane through two sets of independent vascular networks embedded within a ductile polymer substrate beneath the coating. The two reactive components remain isolated and stable in the vascular networks until crack formation occurs in the coating under a mechanical load. Both healing components are wicked by capillary forces into the crack plane, where they react and effectively bond the crack faces closed. Healing efficiencies of over 60% are achieved for up to 16 intermittent healing cycles of a single crack, which represents a significant improvement over systems in which a single monomeric healing agent is delivered. [source]

Numerical simulation of the non-linear crack problem with non-penetration

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 2 2004
Victor A. Kovtunenko
Abstract Here the numerical simulation of some plane Lamé problem with a rectilinear crack under non-penetration condition is presented. The corresponding solids are assumed to be isotropic and homogeneous as well as bonded. The non-linear crack problem is formulated as a variational inequality. We use penalty iteration and the finite-element method to calculate numerically its approximate solution. Applying analytic formulas obtained from shape sensitivity analysis, we calculate then energetic and stress characteristics of the solution, and describe the quasistatic propagation of the crack under linear loading. The results are presented in comparison with the classical, linear crack problem, when interpenetration between the crack faces may occur. Copyright © 2004 John Wiley & Sons, Ltd. [source]