Transient Porosity Research Articles

The Development of a New Sonic Correlation for UCS Estimation from Drilling Data

One of the most important characteristics of rocks in drilling operations is unconfined rock strength (UCS), which is critical in different aspects of drilling operations. Several laboratory-based correlations have been generated for specific rocks to estimate UCS from physical properties (such as transient time, porosity, and Young's modulus) of the rocks. In drilling analysis, when UCS information is required and direct methods for estimation of UCS are not available, it is common to use correlations that have been developed for other formations with the same or similar lithology. Obviously, the results of estimations based on UCS correlations for other formations will not be accurate and can affect subsequent analyses. Therefore, it is highly recommended to generate a correlation for the formation of interest, though it is not always possible to reach this goal from experimental works on core samples retrieved from the formation. In this study, a sonic correlation that shows that it can provide relatively better global estimation of UCS for limestone rocks is modified for one of the Iranian carbonate formations by determining new coefficients for the correlation based on drilling data. For this purpose, the drilling information recorded in mud logging data is analyzed to backward simulate the drilling process based on a modified penetration rate model and calculate the rock strengths of the formation. The apparent rock strength log generated from this calculation proceeds quality-controlled steps according to statistical and pattern recognition methods to eliminate the noises and fluctuations that normally exist while working with field data. Then, a new correlation is developed from the formation response to sonic logs and apparent rock strength log. Because this new correlation is originally generated for the formation of interest, UCS is estimated more accurately and analyses dependent on UCS show fewer errors.

Oxidation of Aluminum Particles in the Presence of Water

Oxidation of spherical aluminum powder was investigated in mixed argon-oxygen-steam atmospheres by thermogravimetric measurements at heating rates between 1 and 20 K/min and up to 1100 degrees C. The observed oxidation behavior in the presence of steam differs markedly from oxidation in dry oxygen. Oxidation in steam is complete near 1000 degrees C vs 1500 degrees C in dry oxygen. Furthermore, in steam, a stepwise weight change is observed at the melting point of aluminum, while no such step can be distinguished in dry oxygen. The complete oxidation observed at a lower temperature in steam as compared to dry oxygen is explained by the stabilization of the gamma polymorph of the surface oxide in the presence of water so that a denser and slower growing alpha-alumina does not form until higher temperatures. Experiments in mixed oxygen/steam oxidizers showed that the size of the oxidation step observed upon aluminum melting only correlates with the concentration of steam in the atmosphere. This may be interpreted as the effect of transient porosity, the degree of which is controlled by the steam concentration, or the surface oxide stressed by the expanding melting metal core may behave as a semipermeable membrane where hydrous species have significantly higher diffusion rates than oxygen. A clear distinction cannot be drawn, and further research is warranted. Preliminary results on isoconversion processing of the oxidation kinetics are presented.

Modeling reactive transport in sediments subject to bioturbation and compaction

Current bioturbation models are marked by confusion in their treatment of porosity. Different equations appear to be needed for different biodiffusion mechanisms, i.e., interphase mixing, where biological activity causes bulk mixing of sediment affecting both tracer and porosity profiles, versus intraphase mixing, where the solid components are intermixed, but the porosity is left unchanged. Another issue is whether the model depends upon the particle type with which tracers are associated, e.g., 137Cs on small clay particles versus 210Pb on larger grains. This uncertainty has lead to conflicting conservation equations for radiotracers, and in particular, to the question whether the porosity should be placed inside or outside of the differential term that governs the biodiffusive flux. We have reexamined this situation in the context of multiphase, multicomponent continuum theory. Most importantly, we prove that under the assumption of steady-state porosity, there exists only one correct form of the steady-state conservation equation for a radiotracer, regardless of biodiffusion mechanism and particle type, i.e., ∂ ∂ x [ φ s D B ∂ C s ∂ x ] − F sed s ρ s ∂ C s ∂ x − ϕ s λ C s = 0 where x is depth, C s is the concentration/activity of the tracer, F sed s is the constant flux of solid sediment to the sediment, ρ s is the density of the solid phase, φ s is the solid volume fraction, D B is the biodiffusion coefficient, and λ is the decay constant. This pertinent finding results from a substantial revision and extension of diagenetic theory. By considering the conservation of momentum, as well as mass, we have identified the correct reference velocities to define biodiffusional fluxes. From that, we have formulated a consistent set of model equations that govern (1) transient porosity and transient tracer concentrations, (2) steady-state porosity and transient tracer concentrations, and (3) steady-state porosity and steady-state tracer concentrations, in sediments that are subject to both compaction and bioturbation.

Textures recording transient porosity in synkinematic quartz veins, South Coast, New South Wales, Australia

The textures of synkinematic veins involve a complex interplay of crystal growth and deformation. Quartz veins in Devonian sandstone and altered felsic volcanic rocks of the South Coast region of New South Wales, Australia, display a range of microstructures recording complex vein growth mechanisms. The synkinematic veins have not suffered significant later imposed deformation and all deformational features within the veins are associated with the kinematics of vein formation. The veins are commonly fibrous but growth patterns are not restricted to simple margin-parallel types (for example, antitaxial and syntaxial). Mineral fibres and blocky cavity fillings developed concurrently throughout all stages of vein growth. Dilation and pressure-solution of vein textures is recorded by transgranular, intergranular, and intragranular deformation microstructures. Textures of progressively deformed synkinematic veins, such as arrays of sigmoidal vein and shear veins related to folding, contain microscopic folds and faults of fibrous quartz and the development of crystallographically controlled microcrack arrays within crystals. Small displacements of the microcrack arrays locally rotate the crystal lattice and at low power magnification are indistinguishable from non-brittle shear bands. Where arrays of veins have been linked to form through-going fault veins, intense deformation microstructures combine with a variety of cavity growth features including dilation of weaknesses such as micaceous seams.

Silicon and oxygen self diffusion in enstatite polycrystals: the Milke et al. (2001) rim growth experiments revisited

Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) studied the diffusion of Si, Mg and O in synthetic polycrystalline enstatite reaction rims. The reaction rims were grown at 1,000°C and 1 GPa at the contacts between forsterite grains with normal isotopic compositions and a quartz matrix extremely enriched in 18O and 29Si. The enstatite reaction rim grew from the original quartz-forsterite interface in both directions producing an inner portion, which replaced forsterite and an outer portion, which replaced quartz. Here we present new support for this statement, as the two portions of the rim are clearly distinguished based on crystal orientation mapping using electron backscatter diffraction (EBSD). Milke et al. (Contrib Mineral Petrol 142:15–26, 2001) used the formalism of LeClaire (J Appl Phys 14:351–356, 1963) to derive the coefficient of silicon grain boundary diffusion from stable isotope profiles across the reaction rims. LeClaire’s formalism is designed for grain boundary tracer diffusion into an infinite half space with fixed geometry. A fixed geometry is an undesired limitation in the context of rim growth. We suggest an alternative model, which accounts for simultaneous layer growth and superimposed silicon and oxygen self diffusion. The effective silicon bulk diffusivity obtained from our model is approximately equal within both portions of the enstatite reaction rim: D Si,En eff =1.0–4.3×10−16 m2 s−1. The effective oxygen diffusion is relatively slow in the inner portion of the reaction rim, D O,En eff =0.8–1.4×10−16 m2 s−1, and comparatively fast, D O,En eff =5.9–11.6×10−16 m2 s−1, in its outer portion. Microstructural evidence suggests that transient porosity and small amounts of fluid were concentrated at the quartz-enstatite interface during rim growth. This leads us to suspect that the presence of an aqueous fluid accelerated oxygen diffusion in the outer portion of the reaction rim. In contrast, silica diffusion does not appear to have been affected by the spatial variation in the availability of an aqueous fluid.

Nickel-catalyzed in situ formation of carbon nanotubes and turbostratic carbon in polymer-derived ceramics

Nickel acetate-impregnated poly(methyl phenyl silsesquioxane) was pyrolyzed in argon atmosphere between 700 and 1000 °C to investigate the influence of the nickel transition metal on the structure evolution of the carbon phase. The formation of the different carbon microstructures and the resulting nanocomposition were studied in detail. The elemental compositions, carbon nanostructures and electrical conductivities of both filler-loaded and filler-free samples at the different temperatures were compared. The filler-loaded samples showed a significantly higher electrical conductivity and a higher carbon-to-hydrogen molar ratio in the investigated temperature range which is attributed to the formation of a percolating turbostratic carbon network already at 700 °C. Thus, the addition of the dehydrogenation-active transition metal Ni leads to a decrease in the starting temperature of the formation of turbostratic carbon by some hundred degrees. Moreover, the formation of multiwall carbon nanotubes was observed within the pores of the filler-loaded polymer matrices. These pores can be regarded as catalytic microreactors. Controlling of the catalyst particle distribution and of the transient porosity generation can enable the development of novel ceramic/carbon nanotube composite materials.

Infiltration of Liquid Metals in Porous Compacts: Modeling of Permeabilities During Reactive Melt Infiltration

Reactive infiltration is a fast and cost-effective technique for manufacturing ceramic-matrix composites (CMCs). CMCs are used in elevated temperature applications like rocket engine casings, jet nozzles, gas turbine blades and nuclear cladding. There is an urgent need for minimizing experimental costs as well as optimizing process parameters during manufacture, so that we have minimized manufacturing costs and reduced infiltration times. Towards this end, the objective of this research was to develop an integrated micro-macro model of reactive flow of molten silicon in a porous preform consisting of carbon-coated silicon carbide fibers and then optimize process parameters computationally. The overall objective of the research was to arrive at a modified equation of Darcy's law for flow through a porous medium with the help of numerical/computational modeling. This paper deals with the flow of silicon through porous carbon at the macro level. The macro flow of silicon was integrated with an available micro model by determining the transient porosity from the micro model and using it in Darcy's law written for the macro flow of silicon. From the results of this study, we recommend suitable process parameters such as initial temperature of the solid reactant and the specific kind of reactants to be used for achieving complete infiltration. These conclusions are drawn after observation of the rate of decrease of permeability with more reaction.

Acid- and Alkali-Resistant Film Generation on an Al-Mn-Ce Alloy

SUMMARYThe growth of anodic films on non-equilibrium Al-16.2 at.% Mn-2.7 at. Ce alloy has been examined in ammonium pentaborate, sodium hydroxide and sulphuric acid electrolytes, providing a pH range from 0.2 to 12. Barrier-type anodic films are developed during anodizing to high voltages, the film growth resulting in formation of a main film material, comprising most of the film thickness, composed of units of Al2O3, MnO and CeO2. The Mn2+ and Ce4+ ions migrate outward faster than Al3+ ions, enabling formation of a thin, manganese-rich and cerium-rich, outermost film layer during anodizing in alkaline conditions. This layer sustains barrier film growth to high pH by allowing ingress of O2- but preventing ejection of Al3+ ions to the electrolyte. In sulphuric acid electrolyte, the outer film layer does not form. Furthermore, the outer 50% of the film contains a reduced amount of cerium, possibly due to transient porosity. However, the film remains relatively resistant to the acid electrolyte, thus hindering the transition to growth of porous film material.

Review and classification of structural controls on fluid flow during regional metamorphism

Mechanisms for kilometre‐scale, open‐system fluid flow during regional metamorphism remain problematic. Debate also continues over the degree of fluid flow channellization during regional metamorphism, and the mechanisms for pervasive fluid flow at depth. The requirements for pervasive long‐distance fluid flow are an interconnected porosity and a large regional gradient in fluid pressure and hydraulic head (thermally or structurally controlled) that dominates over local perturbations in hydraulic head due to deformation. In contrast, dynamic or transient porosity interconnection and fluid flow accompanying deformation of heterogeneous rock suites should result in moderately to strongly channellized flow at a range of scales, of which there are many examples in the literature.Classification of fluid flow types based on scale and degree of equilibration between fluid and rock, wallrock permeability, and mode of fluid transport contributes to an understanding of key factors that control fluid flow. Closed‐system fluid behaviour, with restricted fluid flow in microcracks or cracks and limited fluid–rock interaction, occurs over a range of strains and crustal depths, but requires low permeabilities and/or small fluid fluxes. Long‐distance, open‐system fluid flow in channels is favoured in heterogeneous rocks at high strains, moderate (but variable) permeabilities, and moderate to high fluid fluxes. Long‐distance, broad, pervasive fluid flow during regional metamorphism requires that the rocks are not accumulating high strains and have high permeabilities, low permeability contrasts, and high fluid fluxes. The ideal situation for such fluid flow is in situations where the rocks are undergoing stress relaxation immediately after a major deformation phase. In the mid‐crust, fairly specific conditions are thus required for pervasive fluid flow. During active orogenesis, structurally controlled fluid flow (with focused open systems surrounding regions of closed‐system behaviour) predominates in most, but not all, regional metamorphic situations, at a range of scales.

Why metasomatic fronts are really metasomatic sides

Back-scattered electron microscope images of metasomatic calc-silicate rocks demonstrate complex mineral growth patterns; often oscillatory zoning defines a euhedral or subhedral morphology. We infer from this the existence of an appreciable transient porosity (up to a few percent) during metasomatic calc-silicate growth, and argue that porous, reacting calc-silicate layers become conduits for irreversible metamorphic fluid loss. Because the layers are too permeable to sustain a steep gradient in hydraulic head downdip, fluid pressure in the calc-silicate must generally be lower than in adjacent low-permeability lithologies, so that steep local gradients in the hydraulic head will drive fluid from surrounding rocks up, down, or sideways into the transiently porous reacting layer. So-called “metasomatic fronts” separate transiently permeable layers that have undergone metasomatism from little-altered, low-permeability rocks. Thus they develop parallel to the flow path at its edge and should be termed metasomatic sides.