Matrix Compaction Research Articles

Mechanism of metamorphic fluid expulsion from ductile contact aureole: Insights from numerical modeling of a growing mid-crustal magma chamber

Metamorphic fluid flow around an igneous intrusion is governed by temperature, rheology, permeability and fluid pressure condition in the contact aureole. In the middle crust, where lithostatic fluid pressure and ductile deformation dominate, the impulse from incremental magma chamber growth facilitates ductile aureole compaction and induces syn-intrusive metamorphic devolatilization. However, the mechanism of metamorphic fluid expulsion from ductile contact aureole is vaguely understood. In this study, we numerically modeled the two-phase solid-fluid flow process in the ductile aureole above the growing chamber to examine the potential for fluid expulsion, the pattern of fluid flow and fluid pressure condition. The numerical model is constructed based on the geological structure of the Papoose Flat pluton in California, applying three different modes of pluton growth: continuous growth, episodic growth with an interval of 100 years and episodic growth with an interval of 1000 years. The results indicate that the metamorphic fluids propagate in the form of porosity wave in the ductile aureole with solid matrix compaction. Continuous pluton growth, with a slow pressurization of aureole, leads to a positive fluid pressure anomaly in most of the aureole, whereas the episodic growth results in a negative fluid pressure anomaly at the base and positive fluid pressure anomaly at the top of the aureole. Hydrofracturing can occur in the inner aureole, and the outer aureole may retain some fluid with low-frequency, high-flux magma injections. The solid-fluid flow models indicate that porosity wave is an important mechanism for metamorphic fluid expulsion from the pluton and wall rock system.

Optimization of asphalt mixture design based on the compressible packing model

Traditional design methods seldom consider accumulation properties, which influence the structure of asphalt mixtures. Therefore, this study is the first to put forward a modified compressible packing model. The filling characteristics of coarse aggregate were studied. Different matrix compaction indexes η and compaction indexes K were selected to study the influence of the modified compressible model on pavement performance. Design methods based on a 4% air void and minimum voids in mineral aggregate were compared through the volumetric parameters and pavement performance based on the modified compressible packing model. The asphalt mixture performances with three gradations were analyzed. The test results showed that as the matrix compaction index η decreased, the optimum asphalt content of both methods increased, while the VMA decreased. Finally, an optimized asphalt mixture design method based on the compressible packing model was proposed, which showed good prospects for application.

On the peculiarities of using sparse matrices in problems of mathematical modeling

Mathematical modeling and the related computer experiment are now one of the main means of studying objects, processes and phenomena of various nature: in science, engineering, economics, society, etc. A significant improvement in the quality of mathematical modeling in many areas of science and engineering is possible only with the use of fundamentally new three-dimensional models, the transition from computer simulation of individual components and assemblies to the calculation and optimization of the product as a whole. It is obvious that the consideration of problems in such a formulation leads to discrete mathematical models of super-large sizes. Existing supercomputers of different parallel architectures make it possible to efficiently solve such problems. However, the time for solving problems on parallel computers consists of the time of the actual solution and the time of performing additional operations, that are necessary for the exchange of information between computing devices, that is overhead costs. This is especially true for problems of linear algebra with different structures of sparse matrices of large volumes, that arise in the mathematical modeling of processes. Sparse matrix compaction schemes, decomposition of data arrays between processors are one of the main factors for the effective solution of these problems on parallel computers. The paper considers efficient methods for processing sparse matrices of arbitrary structure for the purpose of effective mathematical modeling of structural strength problems on parallel computers. Various methods of regularization and decomposition of sparse matrices of arbitrary structure, efficient data storage schemes, technology for studying the conditionality of a matrix with approximate data on a computer are proposed. This way of using sparse matrices in mathematical modeling ensures more efficient use of computing resources and reliability of computer results. Problems of mathematical modeling are presented, where the considered methods of processing sparse matrices were effectively applied.

Mechanosensor YAP cooperates with TGF-β1 signaling to promote myofibroblast activation and matrix stiffening in a 3D model of human cardiac fibrosis

Cardiac fibrosis is characterized by a maladaptive remodeling of the myocardium, which is controlled by various inflammatory pathways and cytokines. This remodeling is accompanied by a significant stiffening of the matrix, which may contribute to further activate collagen synthesis and scar formation. Evidence suggests that TGF-β1 signaling, the main pro-fibrotic pathway in cardiac fibrosis, might cooperates with the Hippo transcriptional pathway by activating YAP. To directly test the cooperation of mechanical cues and paracrine signaling in cardiac fibrosis, we developed a 3D model of cardiac extracellular matrix remodeling by generating tissue blocks with Gelatin Methacrylate, a bioink with tunable stiffness, and human cardiosphere-derived stromal cells. Using this strategy, we assessed the cooperation of TGF-β1 and YAP transcriptional factor to matrix compaction. Using mechanical compression tests, Masson's trichrome staining, immunofluorescence, and RT-qPCR, we demonstrate that pharmacological inhibition of YAP complex reverts almost completely the pro-compaction phenotype and the matrix-remodeling activity of cells treated with TGF-β1. Our data show a direct connection between the classical pro-fibrotic signaling driven by TGF-β1 and the mechanically activated pathways under the control of YAP in cardiac remodeling. Treatment with the elective drug targeting YAP is sufficient to override this cooperation with potential benefits for anti-fibrotic therapeutic applications. Statement of significanceHeart failure is a pathology in continuous growth worldwide, characterized by a progressive fibrosis, which decreases the pumping efficiency of the heart. Experimental evidences suggest that fibroblasts, normally responsible for the turnover of the cardiac matrix, are involved in myocardial fibrosis by differentiating into ‘myofibroblasts’. These cells remodel extensively the cardiac extracellular matrix and deposit abundant collagen with a consequent increase in stiffness. In the present contribution, we propose a new 3D model of cell-mediated cardiac extracellular matrix stiffening to investigate the mechano-chemical mechanisms underlying the onset of the pathology. We also consolidate a pharmacological treatment able to prevent the pathological activation of fibroblasts with potential benefits for anti-fibrotic treatment of the failing heart.

The interstitial compartment as a therapeutic target in heart failure.

Congestion is the single most important contributor to heart failure (HF) decompensation. Most of the excess volume in patients with HF resides in the interstitial compartment. Inadequate decongestion implies persistent interstitial congestion and is associated with worse outcomes. Therefore, effective interstitial decongestion represents an unmet need to improve quality of life and reduce clinical events. The key processes that underlie incomplete interstitial decongestion are often ignored. In this review, we provide a summary of the pathophysiology of the interstitial compartment in HF and the factors governing the movement of fluids between the interstitial and vascular compartments. Disruption of the extracellular matrix compaction occurs with edema, such that the interstitium becomes highly compliant, and large changes in volume marginally increase interstitial pressure and allow progressive capillary filtration into the interstitium. Augmentation of lymph flow is required to prevent interstitial edema, and the lymphatic system can increase fluid removal by at least 10-fold. In HF, lymphatic remodeling can become insufficient or maladaptive such that the capacity of the lymphatic system to remove fluid from the interstitium is exceeded. Increased central venous pressure at the site of the thoracic duct outlet also impairs lymphatic drainage. Owing to the kinetics of extracellular fluid, microvascular absorption tends to be transient (as determined by the revised Starling equation). Therefore, effective interstitial decongestion with adequate transcapillary plasma refill requires a substantial reduction in plasma volume and capillary pressure that are prolonged and sustained, which is not always achieved in clinical practice. The critical importance of the interstitium in the congestive state underscores the need to directly decongest the interstitial compartment without relying on the lowering of intracapillary pressure with diuretics. This unmet need may be addressed by novel device therapies in the near future.

Synergistic effect of surfactant and chlorine salt on dispersion of nano-SiO2 and performance of cement-based grout containing a large amount of bentonite

Nano-SiO2 (NS) is widely used to improve the performance of cement-based grouts. The workability and mechanical property of grouts are greatly affected by NS dispersion. In this paper, synergistic effect of surfactants and chloride salts on NS dispersion, as well as on performance of grouts including fluidity, mechanical and microscopic properties were systemically studied. The results showed that the synergistic effect of anionic surfactant (SDS) and chloride salt can effectively improve NS dispersion because of the massive formation of micelles that can encapsulate NS and the electrostatic repulsion between micelles. And the effect of CaCl2 was more significant than NaCl. Furthermore, fluidity of fresh slurry and mechanical property of hardened grouts were also improved by the synergistic effect. The mechanical property enhancement might be attributed to the filling effect of NS due to its improved dispersion, and to the matrix compaction associated with the formation of strätlingite and Friedel's salt.

Formation of chondrule fine‐grained rims from local nebular reservoirs

AbstractChondrules are commonly surrounded by fine‐grained rims (FGRs) whose origin remains highly debated; both nebular and parent body settings are generally proposed. Deciphering their origin, however, is of fundamental importance as they could clarify the matrix–chondrule relationship and thus constrain the formation and transport conditions of chondrules in the circumsolar disk. Here, we report a systematic survey of FGRs in CO, CM, CV, and CR chondrites; we compare (i) the thickness of FGRs to the size of their host chondrules and (ii) the frequency of FGRs to the modal abundance of matrix in the respective host chondrites. Although FGRs show textural variations depending on the petrologic type of the considered chondrites, our data show a positive correlation between apparent rim thickness and the radius of the host chondrule in all chondrite groups. We also found a positive correlation between the evaluated percentages of rimmed chondrules and the modal abundance of matrix material in the chondrites. We show that this relationship could not result from parent body processes, whether matrix compaction or FGR fragmentation. Therefore, we propose that FGRs were accreted under warm conditions at the end of chondrule‐forming events. Our results thus support (i) a nebular origin for FGR, whose abundances are directly related to the abundance of available dust in regions of chondrite accretion; and (ii) the accretion of chondrites from locally formed chondrules and matrix, suggesting limited radial transport in the protoplanetary disk.

Spatiotemporal control of myofibroblast activation in acoustically-responsive scaffolds via ultrasound-induced matrix stiffening

Hydrogels are often used to study the impact of biomechanical and topographical cues on cell behavior. Conventional hydrogels are designed a priori, with characteristics that cannot be dynamically changed in an externally controlled, user-defined manner. We developed a composite hydrogel, termed an acoustically-responsive scaffold (ARS), that enables non-invasive, spatiotemporally controlled modulation of mechanical and morphological properties using focused ultrasound. An ARS consists of a phase-shift emulsion distributed in a fibrin matrix. Ultrasound non-thermally vaporizes the emulsion into bubbles, which induces localized, radial compaction and stiffening of the fibrin matrix. In this in vitro study, we investigate how this mechanism can control the differentiation of fibroblasts into myofibroblasts, a transition correlated with substrate stiffness on 2D substrates. Matrix compaction and stiffening was shown to be highly localized using confocal and atomic force microscopies, respectively. Myofibroblast phenotype, evaluated by α-smooth muscle actin (α-SMA) immunocytochemistry, significantly increased in matrix regions proximal to bubbles compared to distal regions, irrespective of the addition of exogenous transforming growth factor-β1 (TGF-β1). Introduction of the TGF-β1 receptor inhibitor SB431542 abrogated the proximal enhancement. This approach providing spatiotemporal control over biophysical signals and resulting cell behavior could aid in better understanding fibrotic disease progression and the development of therapeutic interventions for chronic wounds. Statement of SignificanceHydrogels are used in cell culture to recapitulate both biochemical and biophysical aspects of the native extracellular matrix. Biophysical cues like stiffness can impact cell behavior. However, with conventional hydrogels, there is a limited ability to actively modulate stiffness after polymerization. We have developed an ultrasound-based method of spatiotemporally-controlling mechanical and morphological properties within a composite hydrogel, termed an acoustically-responsive scaffold (ARS). Upon exposure to ultrasound, bubbles are non-thermally generated within the fibrin matrix of an ARS, thereby locally compacting and stiffening the matrix. We demonstrate how ARSs control the differentiation of fibroblasts into myofibroblasts in 2D. This approach could assist with the study of fibrosis and the development of therapies for chronic wounds.

Macroscopically healthy articular cartilage with fibrillar-scale early tissue degeneration subject to impact loading results in greater extent of cell-death

From previous investigations it has been shown that there exists healthy-appearing articular cartilage that contains collagen fibril network destructuring. It is hypothesised that such sub-micron scale destructuring not only presents an increased vulnerability to tissue scale damage following impact loading, but an increase in cell death as well.Cartilage-on-bone blocks from 12 patellae, six healthy (G0) and the other six with sub-micron fibrillar destructuring (G1), were obtained and subject to 2.3 J impact loading. Two sets of sub-samples were obtained for each block tested. One set was used to examine for the live/dead cell response using calcein-AM and propidium iodide staining, imaged with confocal microscopy. The tissue microstructural matrix was imaged from the other matched set, unstained and in its fully hydrated state, using differential interference contrast optical light microscopy. High speed imaging of the impact was used to calculate the velocity changes or coefficient of restitution (COR) and used as a proxy of energy that the tissue absorbed. A previously defined tissue matrix damage score was used to quantify the extent of fracturing and cracking in the matrix. The cell death (PCD) was counted and presented as a percentage against all cells live plus dead.The energy absorbed was 36.5% higher in G1 than in G0 (p = 0.034). However, the damage score and PCD of samples in the G1 group was much larger than the G0 group, ~300% and 161% respectively. Microscopy showed that cell death is associated to both matrix compaction and further fibrillar destructuring from the ECM to the territorial matrix regions of the chondron.Following impact loading, cartilage tissue that appears normal but contains sub-micron fibrillar matrix destructuring responds with significantly increased cell death.

Spatially-directed cell migration in acoustically-responsive scaffolds through the controlled delivery of basic fibroblast growth factor

Hydrogels are commonly used in regenerative medicine for the delivery of growth factors (GFs). The spatial and temporal presentations of GFs are critical for directing regenerative processes, yet conventional hydrogels do not enable such control. We have developed a composite hydrogel, termed an acoustically-responsive scaffold (ARS), where release of a GF is non-invasively and spatiotemporally-controlled using focused ultrasound. The ARS consists of a fibrin matrix doped with a GF-loaded, phase-shift emulsion. The GF is released when the ARS is exposed to suprathreshold ultrasound via a mechanism termed acoustic droplet vaporization. In this study, we investigate how different spatial patterns of suprathreshold ultrasound can impact the biological response upon in vivo implantation of an ARS containing basic fibroblast growth factor (bFGF). ARSs were fabricated with either perfluorohexane (bFGF-C6-ARS) or perflurooctane (bFGF-C8-ARS) within the phase-shift emulsion. Ultrasound generated stable bubbles in bFGF-C6-ARS, which inhibited matrix compaction, whereas transiently stable bubbles were generated in bFGF-C8-ARS, which decreased in height by 44% within one day of implantation. The rate of bFGF release and distance of host cell migration were up to 6.8-fold and 8.1-fold greater, respectively, in bFGF-C8-ARS versus bFGF-C6-ARS. Ultrasound increased the formation of macropores within the fibrin matrix of bFGF-C8-ARS by 2.7-fold. These results demonstrate that spatially patterning suprathreshold ultrasound within bFGF-C8-ARS can be used to elicit a spatially-directed response from the host. Overall, these findings can be used in developing strategies to spatially pattern regenerative processes. Statement of SignificanceHydrogels are commonly used in regenerative medicine for the delivery of growth factors (GFs). The spatial and temporal presentations of GFs are critical for directing regenerative processes, yet conventional hydrogels do not enable such control. We have developed a composite hydrogel, termed an acoustically-responsive scaffold (ARS), where GF release is non-invasively and spatiotemporally-controlled using focused ultrasound. The ARS consists of a fibrin matrix doped with a phase-shift emulsion loaded with GF, which is released when the ARS is exposed to ultrasound. In this in vivo study, we demonstrate that spatially patterning ultrasound within an ARS containing basic fibroblast growth factor (bFGF) can elicit a spatially-directed response from the host. Overall, these findings can be used in developing strategies to spatially pattern regenerative processes.

A Dual-Grid, Implicit, and Sequentially Coupled Geomechanics-and-Composition Model for Fractured Reservoir Simulation

SummaryIn the development of fractured reservoirs, geomechanics is crucial because of the stress sensitivity of fractures. However, the complexities of both fracture geometry and fracture mechanics make it challenging to consider geomechanical effects thoroughly and efficiently in reservoir simulations. In this work, we present a coupled geomechanics and multiphase-multicomponent flow model for fractured reservoir simulations. It models the solid deformation using a poroelastic equation, and the solid deformation effects are incorporated into the flow model rigorously. The noticeable features of the proposed model are it uses a pseudocontinuum equivalence method to model the mechanical characteristics of fractures; the coupled geomechanics and flow equations are split and sequentially solved using the fixed-stress splitting strategy, which retains implicitness and exhibits good stability; and it simulates geomechanics and compositional flow, respectively, using a dual-grid system (i.e., the geomechanics grid and the reservoir-flow grid). Because of the separation of the geomechanics part and the flow part, the model is not difficult to implement based on an existing reservoir simulator. We validated the accuracy and stability of this model through several benchmark cases and highlighted the practicability with two large-scale cases. The case studies demonstrate that this model is capable of considering the key effects of geomechanics in fractured-reservoir simulation, including matrix compaction, fracture normal deformation, and shear dilation, as well as hydrocarbon phase behavior. The flexibility, efficiency, and comprehensiveness of this model enable a more realistic geocoupled reservoir simulation.

High-Performance Concretes Intended for Deep Foundations of Constructions

The term high-performance concrete (HPC) can be used to classify any concrete mixture that possesses some added value. One such category of concrete is concrete mixtures used in pile foundation, which must only allow a low degree of water separation (bleeding). The basic components of production of these concretes with high utility properties include the usability of active and passive admixtures and their mutual combinations. As part of this research, analysis of aspects affecting water separation from fresh concrete mixture, including dosing, and the type of individual raw materials, was performed. This article aims to utilise these results to analyse the impact of individual components and to provide a comprehensive theory for how to optimise the design of low-bleeding HPC based on the appropriate selection and mixing ratio of cement and admixture. A set of different raw materials and the effect of their mutual mixing ratios on bleeding and other mechanical and physical parameters of produced mixtures were verified. The results of this experiment demonstrate the clear relationship between the amount of binders up to size 0.25 mm and amount of water that separates under pressure. Very important aspect is morphology of grains used binders. These knowledge of realized experiment could be easily applied into the practise, same as designed methodology of usage combination of active and passive admixtures to create a maximum cement matrix compaction.

Microglia and macrophages promote corralling, wound compaction and recovery after spinal cord injury via Plexin-B2.

Tissue repair after spinal cord injury (SCI) requires mobilization of immune and glial cells to form a protective barrier that seals the wound and facilitates debris clearing, inflammatory containment, and matrix compaction. This process involves corralling, wherein phagocytic immune cells become confined to the necrotic core surrounded by an astrocytic border. Here, we elucidate a temporally distinct gene signature in injury-activated microglia/macrophages (IAM), which engages axon guidance pathways. Plexin-B2 is upregulated in IAM, which is required for motosensory recovery after SCI. Plexin-B2 deletion in myeloid cells impairs corralling, leading to diffuse tissue damage, inflammatory spillover, and hampered axon regeneration. Corralling begins early and requires Plexin-B2 in both microglia and macrophages. Mechanistically, Plexin-B2 promotes microglia motility, steers IAM away from colliding cells, and facilitates matrix compaction. Our data thus establish Plexin-B2 as an important link that integrates biochemical cues and physical interactions of IAM with the injury microenvironment during wound healing.

A new concept for the extraction of gas from Permian ultra-deep coal seams of the Cooper Basin, Australia: Expanding Reservoir Boundary Theory

An alternative geomechanical reservoir boundary condition is proposed for ultra-deep coal seams of the Cooper Basin in central Australia. This new concept is embodied within the author’s ‘Expanding Reservoir Boundary (ERB) Theory’, which calls for a paradigm shift in gas extraction technology, diametrically opposed to current practices. As with shale, full-cycle, standalone commercial gas production from Cooper Basin ultra-deep coal seams requires a large stimulated reservoir volume (SRV) having high fracture surface area for gas desorption. This goal has not yet been achieved after 13 years of trials because, owing to the bipolar combination of shale-like reservoir properties and coal-like geomechanical properties, these poorly cleated, inertinitic coal seams exhibit ‘hybrid’ characteristics. Stimulation techniques adopted from other play types are incompatible with the highly unfavourable combination of nanoDarcy-scale permeability, ‘ductility’ and high stress. Nevertheless, gas flow potential counterintuitively increases with depth, contingent upon the creation of an effective SRV. Optimum reservoir conditions occur at depths beyond 9000 feet (2740 m), driven by dehydration, high gas content, gas oversaturation, overpressure and a rigid host rock framework. The physical response of ultra-deep coal seams and the surrounding host rock to pressure drawdown is inadequately characterised. It remains to be established how artificial fracture and coal fabric aperture width change due to the competition between desorption-induced coal matrix shrinkage and compaction caused by increasing effective stress. Studies by the author suggest that pressure arching may ultimately control gas extraction efficiency. Harnessing this geomechanical phenomenon could resolve the technical impasse that currently inhibits commercialisation. Pressure arching neutralises SRV compaction by deflecting stress to adjacent strata of greater integrity. These strata then function as an abutment for accommodating increased stress outside the SRV. This shielding effect allows producing ultra-deep coal seams to progressively de-stress and ‘self-fracture’ naturally, in an overall state of shrinkage-induced tensile failure. An ‘expanding reservoir boundary and decreasing confining stress’ condition is generated by the combined, mutually sustaining actions of coal matrix shrinkage and sympathetic pressure arch evolution. This causes the SRV to steadily increase in size and permeability. Cooper Basin ultra-deep coal seams may be effectively stimulated by harnessing this self-perpetuating, depth-resistant mechanism for creating permeability and surface area. The ultra-deep coal seams may be induced to pervasively ‘shatter’ or ‘self-fracture’ naturally during production, independent of ‘brittleness’, analogous to the manner in which shrinkage crack networks slowly form, in a state of intrinsic tension, within desiccating clay-rich surface sediment.

Hybrid slag geopolymer composites with durable characteristics activated by cement kiln dust

The effect of sulfate solution on the geopolymer formed from different type of slag as arc slag (EAFS) and granulated blast furnace slag (GGBFS) as well as cement kiln dust (CKD) was studied. Activation was carried upon usage of 25% CKD, as it bears high alkali content that can initiate and propagate the polymerization process. The formed geopolymer composites were immersed in 5% MgSO4 solution to determine the stability upon sulfate attack. FTIR, XRD, SEM, compressive strength and water absorption analysis were utilized to examine the obtained geopolymer under sulfate attack. Results clarified an optimization of strength values by EAFS increase up to 50%, followed by lowering in strength with EAFS increase, possessing stability up to 12 months. Data elucidated a good stability and resistance of mix containing slag substitution by 50% EAFS and 25% GGBFS and resulted in further enhancement in both mechanical and micro-structural characteristics by increasing matrix compaction and cohesion than the non-immersed samples (28 days).

Valorization of cement kiln dust in activation and production of hybrid geopolymer composites with durable characteristics

The main target of the present paper is valorize the high alkalis in cement kiln dust for production of sustainable hybrid alkali activated composites, where these high alkalis content prohabit its recycle in building materials. The used precursors are electric arc slag (EAFS) and granulated blast furnace slag (GGBFS) as well as cement kiln dust (CKD) was studied. Activation was carried upon usage of 25% CKD, as it bears high alkali content that can initiate and propagate the polymerization process. The formed geopolymer composites were immersed in 5% MgSO4 solution to determine the stability upon sulfate attack. FTIR, XRD, SEM, compressive strength, and water absorption analysis were utilized to examine the obtained geopolymer under sulfate attack. Results clarified the potentiality of cement kiln dust in production of alkali activated composites with durable properties in sulfate solution and possess an optimization of strength values by EAFS up to 50%, followed by lowering in strength with EAFS increase, although possessing stability up to 12 months. Data elucidated a good stability and resistance of mix containing slag substitution by 50% EAFS and 25% GGBFS and resulted in further enhancement in both mechanical and microstructural characteristics by increasing matrix compaction and cohesion than the non-immersed samples (28 days).

On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

AbstractThe solidification of a putative magma ocean sets the stage for subsequent subsolidus mantle convection. Whereas it may have resulted in a compositionally stratified mantle, the efficiency of relevant processes to cause chemical differentiation, such as crystal accumulation and matrix compaction, remains uncertain. The purpose of this study is to present the thermochemical structure of end‐member cases where potential differentiation mechanisms are taking full effect. We employ a self‐consistent thermodynamic model to make our model consistent in both thermal and chemical aspects. The accumulation of crystals at the base of magma ocean can enrich the upper mantle with iron, but such a global‐scale compositional stratification is likely to be quickly eliminated by gravitational instability, leaving small‐scale heterogeneities only. On the other hand, the compaction of solid matrix in the deep mantle creates a long‐lasting molten layer above the core‐mantle boundary. Our results suggest that the efficiency of compaction is the key factor to generate compositional stratification during solidification.

Stress-Dependent Permeability of Fractures in Tight Reservoirs

Permeability is one of the key factors involved in the optimization of oil and gas production in fractured porous media. Understanding the loss in permeability influenced by the fracture system due to the increasing effective stress aids to improve recovery in tight reservoirs. Specifically, the impacts on permeability loss caused by different fracture parameters are not yet clearly understood. The principal aim of this paper is to develop a reasonable and meaningful quantitative model that manifests the controls on the permeability of fracture systems with different extents of fracture penetration. The stress-dependent permeability of a fracture system was studied through physical tests and numerical simulation with the finite element method (FEM). In addition, to extend capability beyond the existing model, a theoretical stress-dependent permeability model is proposed with fracture penetration extent as an influencing factor. The results presented include (1) a friendly agreement between the predicted permeability reduction under different stress conditions and the practical experimental data; (2) rock permeability of cores with fractures first reduces dramatically due to the closure of the fractures, then the permeability decreases gradually with the increase in effective stress; and (3) fracture penetration extent is one of the main factors in permeability stress sensitivity. The sensitivity is more influenced by fracture systems with a larger fracture penetration extent, whereas matrix compaction is the leading influencing factor in permeability stress sensitivity for fracture systems with smaller fracture penetration extents.

Investigation of gas slippage effect and matrix compaction effect on shale gas production evaluation and hydraulic fracturing design based on experiment and reservoir simulation

Recent core-lab study of Marcellus Shale illustrated that effect of gas slippage and matrix compaction are significant on gas production because of substantial reservoir pressure depletion, especially during the late time of gas production. However, the impact of gas slippage and matrix compaction on gas recovery evaluation and hydraulic fracturing design is still not clearly understood and systematically investigated. Additionally, such impact varies with production time and completion/production circumstances. Therefore, it is critical to develop a laboratory-modeling based approach that properly characterizes the two permeability effects and evaluates their impact on well production evaluation and hydraulic fracturing design.In this study, a comprehensive parametric study is conducted by running reservoir simulations using empirical permeability correlations developed from core-lab tests under different confining stress and pore pressure conditions. Simulations of different case scenarios are run in two contrast groups. One group considers the effect of gas slippage and matrix compaction on gas production and the other group ignores the two effects. By comparing the simulated gas production, critical conductivity, and proppant pumping amount/cost of the two contrast groups, a better understanding of the effect of gas slippage and geomechanics on shale gas well performance and hydraulic fracturing design can be developed for operators. The results show that ignoring the two permeability effect in reservoir simulation leads to an overestimation of gas production evaluation, which is up to 11% for Marcellus Shale. It also leads to an over-design of proppant pumping amount, resulting in early staging, screening-out, and excessive pumping cost. Calculations further show that, an average of over 2 million dollars can be wasted for fracturing a single horizontal well in Marcellus Shale if excluding the two effect from a fracturing design. The two effects are more significant for lower BHP, longer hydraulic fracture, and larger stage spacing conditions.

Effects of fluid influx, fluid viscosity, and fluid density on fluid migration in the mantle wedge and their implications for hydrous melting

The migration pathways of hydrous fluids in the mantle wedge are influenced by the compaction of the porous mantle matrix, which depends on the matrix permeability, fluid viscosity, and fluid density. Experimental studies show that when fluids are interconnected, the permeability depends on mineral grain size and porosity, the latter of which depends on the amount of fluids introduced into the system (fluid influx). Here, we investigate the role of fluid influx, fluid viscosity, and fluid density in controlling fluid migration in the mantle wedge, using a 2-D numerical model accounting for the effects of grain-size variation and matrix compaction. Our models predict that fluid influx and fluid viscosity are key controls on fluid pathways, while fluid density plays a secondary role. Temperature dependence of fluid viscosity promotes downdip drag of fluids at the base of the forearc mantle toward the subarc region. High fluid influx at postarc depths promotes updip flow near the base of the mantle wedge, guiding the fluids arcward. The model that is applied to northern Cascadia predicts upward fluid migration focused beneath the arc but cannot explain high electrical conductivity observed slightly west of the upward fluid migration. We estimate the amount of hydrous melt that can be produced in the mantle wedge using calculated fluid distributions. Up to a few percent partial melting is predicted in a relatively small region in the core part of the subarc mantle wedge in most subduction settings, including northern Cascadia, and beneath the backarc in old-slab subduction zones.