Microscale Pores Research Articles

Comparisons of fracturing mechanism of tight sandstone using liquid CO2 and water

CO2 is recently applied as fracturing liquid in exploitation of tight oil and gas resources and could significantly increase the oil and gas production. However, the changes in micro-scale pore and crack and in macro-crack due to liquid CO2 fracturing are still not completely understood and need multi-scale investigation. In this study, liquid CO2 and water fracturing tests were performed on tight sandstone under different confining pressure to analyze their different fracturing mechanism. Three methods (CT scanning, 3-D fracture morphology scanning and NMR measurement) were applied to identify pore and crack characteristics of fractured samples from micro-to macro-scale. Comparing with water fracturing, liquid CO2 fracturing can significantly reduce the breakdown pressure under the same confining pressure. The breakdown pressures using both water fracturing and liquid CO2 fracturing increase with increasing confining pressure, while the increasing ratio of the latter one is larger. For liquid CO2 fracturing, CT scanning results show that fractures tend to deflect and produce secondary branched cracks in the direction of propagation, and fracture tortuosity is greater than that of water fracturing. Moreover, NMR results show water fracturing mainly produces large-scale macro-cracks, whereas both large-scale macro-cracks and micro-scale cracks could be observed for liquid CO2 fracturing. The main reason is that the liquid CO2 permeation generates more the micro-scale cracks, and induces irreversible crack initiation and preferred propagation, resulting in more tortuous fracture plane and lower breakdown pressure. The test results could improve our knowledge of CO2 fracturing in unconventional oil/gas exploitation.

A Spatial-Scale Evaluation of Soil Consolidation Concerning Land Subsidence and Integrated Mechanism Analysis at Macro-, and Micro-Scale: A Case Study in Chongming East Shoal Reclamation Area, Shanghai, China

Land reclamation has been increasingly employed in many coastal cities to resolve issues associated with land scarcity and natural hazards. Especially, land subsidence is a non-negligible environmental geological problem in reclamation areas, which is essentially caused by soil consolidation. However, spatial-scale evaluation on the average degree of consolidation (ADC) of soil layers and the effects of soil consolidation on land subsidence have rarely been reported. This study aims to carry out the integrated analysis on soil consolidation and subsidence mechanism in Chongming East Shoal (CES) reclamation area, Shanghai, at spatial-, macro-, and micro-scale so that appropriate guides can be provided to resist the potential environmental hazards. The interferometric synthetic aperture radar (InSAR) technique was utilized to retrieve the settlement curves of the selected onshore (Ra) and offshore (Rb) areas. Then, the hyperbolic (HP) model and three-point modified exponential (TME) model were combined applied to predict the ultimate settlement and to determine the range of ADC rather than a single pattern. With two boreholes Ba and Bb set within Ra and Rb, conventional tests, MIP test, and SEM test were conducted on the collected undisturbed soil to clarify the geological features of exposed soil layers and the micro-scale pore and structure characteristics of representative compression layer. The preliminary results showed that the ADC in Rb (93.1–94.1%) was considerably higher than that in Ra (60.8–78.7%); the clay layer was distinguished as the representative compression layer; on micro-scale, the poor permeability conditions contributed to the low consolidation efficiency and slight subsidence in Rb, although there was more compression space. During urbanization, the offshore area may suffer from potential subsidence when it is subjected to an increasing ground load, which requires special attention.

Experimental Investigation of the CO2 Huff and Puff Effect in Low-Permeability Sandstones with NMR.

For low-permeability sandstone reservoirs, CO2 huff and puff is an effective method for increasing oil recovery. Commonly, sandstone formations with low permeability have diverse pore and throat sizes and a complex pore-throat structure, which essentially affects the flow characteristics of CO2 and oil in the formation and further the CO2 huff and puff performance. It is necessary to understand the recovery degree of various microscale pore sizes under different operational parameters during CO2 huff and puff in tight sandstones. In this work, several experiments of cyclic CO2 injection are conducted with sandstone core samples with low permeability. Before and after the injection, the T2 spectra of the sandstone cores are compared using the NMR technique. We then discuss the micro residual oil distribution and recovery degree in different pores, such as micropores (<1 ms), small pores (1–10 ms), medium pores (10–100 ms), and macropores (>100 ms). It is found that the recovery degree in the different pores increases as the pore size increases. Oil can be recovered more easily from macropores and medium pores during the cyclic CO2 injection. The oil contained in micropores is relatively difficult to extract considering a high capillary force under immiscible conditions. It is found that the total recovery degree increases with the increase in soaking time. However, such a recovery degree increment in small pores is not as large as that achieved in medium and large pores. With the CO2 injection volume increase, the total recovery degree increases. When the CO2 injection volume is less than 1.5 PV, it is challenging to extract the oil from micropores and small pores. As the cycle number increases, the cyclic oil recovery decreases, and most of the oil is produced in the first cycle. This suggests that under the experimental conditions of this study, the cycle number of CO2 huff and puff shall not be more than 3. This work is important to further understand the CO2 huff and puff process for improving oil recovery in sandstone reservoirs with low permeability.

The role of micro-inertia on the shock structure in porous metals

The behavior of porous materials under shock loading is a multi-scale problem bridging orders of magnitude across the macroscale geometry and the microscale pores. Under static loading, this problem is well understood, relating mechanisms of pore closure and crushing to the equivalent macroscale models. The dynamic response of porous solids under shock loading is related to the effects of viscoplasticity and micro-acceleration fields around the void boundaries. The significance of the micro-inertia effects in modeling the dynamic behavior of porous materials remains an open question. In this work, an experimental investigation on closed-cell porous aluminum with small porosity provides the evidence for the first time of micro-inertia's fundamental role in describing the shock structure in these materials. Materials with different levels of porosity were manufactured using a modified process of additive manufacturing to achieve a mean pore size below 50μm. Plate impact experiments on porous aluminum samples were conducted at pressures in the range of 2 to 11 GPa. The structure of the steady shock was characterized as a function of porosity and shown to validate behavior revealed by an analytical approach (Czarnota et al. [J. Mech. Phys. Solids 107 (2017)]), highlighting the fundamental role of micro-inertia effects in such cases.

Formation of inhomogeneous micro-scale pores attributed ultralow κlat and concurrent enhancement of thermoelectric performance in p-type Bi0.5Sb1.5Te3 alloys

In the background of enhancing thermoelectric (TE) figure of merit of solid-state materials, the introduction of porous structure can significantly decrease lattice thermal conductivity by intensifying phonon scattering at the inhomogeneous microscale pores. Herein, we developed a porous structure in Cu0.07Bi0.5Sb1.5Te3 compounds by utilizing PVA as the pore former, and systematically studied its effect on thermoelectric properties. The results revealed that the reduction in thermal conductivity (~28%) was greater than the decrease in electrical conductivity (~17%) with increasing porosity, indicating long-wavelength phonon scattering was enhanced at micro-scale pores. Consequently, a peak zT of 1.342 at 400 K, and a zTavg of 1.254 in the temperature range of 300–500 K and an ηmax of ~9.4% at ΔT = 200 K were achieved in the porous sample (10.58%), which all are higher than that of dense sample. The hardness and compressive strength of the porous samples were significantly higher than commercial zone melting ingots. The proposed methodology is a cost-effective and efficient way of producing high-performance TE devices with good mechanical stability for real life practical applications.

Permeability variation analysis using the superficial diameter correlation with porosity change

Permeability characterization is a major factor for ensuring more environment-friendly operations and economically viable industrial applications related to carbon capture sequestration, hydrocarbon recovery, nuclear waste disposal, and remediation in groundwater. Regardless, the permeability variation caused by changes in formation stress is simply defined as the power-law function of porosity. An alternative formula can be presented using the Kozeny–Carman equation based on hydraulic diameter and tortuosity. However, the hydraulic tortuosity and the Kozeny constant cannot be precisely measured because of the extremely complex and microscale pores. Accordingly, this study considers the Kozeny–Carman equation for presenting the other definable variables and more general correlations for performing permeability variation analyses. Herein, the effective tortuosity and effective and superficial diameters of porous media are deduced adopting the conventional viscous flow theory. Subsequently, the Kozeny–Carman equation is improved by replacing the immeasurable variables with the effective variables. The correlations of all the key geometric variables with permeability variation are investigated via pore-scale simulations based on two types of 20-series porous medium models with a wide range of porosity (13.4%–47.4%) and permeability (0.0073 –18.3 Darcy). Herein, several impressive functional aspects of the superficial diameter were discovered with porosity changes, such as quadratic functional correlations, parallel shifts for each flow path, and less sensitive variations in low porosity ranges. Consequently, this study proved that permeability variations can be more precisely and generally estimated using the quadratic correlations of the superficial diameter with porosity changes.

Fluid interfacial energy drives the emergence of three-dimensional periodic structures in micropillar scaffolds

Structures that are periodic on a microscale in three dimensions are abundant in nature, for example, in the cellular arrays that make up living tissue. Such structures can also be engineered, appearing in smart materials1–4, photonic crystals5, chemical reactors6, and medical7 and biomimetic8 technologies. Here we report that fluid–fluid interfacial energy drives three-dimensional (3D) structure emergence in a micropillar scaffold. This finding offers a rapid and scalable way of transforming a simple pillar scaffold into an intricate 3D structure that is periodic on a microscale, comprising a solid microscaffold, a dispersed fluid and a continuous fluid. Structures generated with this technique exhibit a set of unique features, including a stationary internal liquid–liquid interface. Using this approach, we create structures with an internal liquid surface in a regime of interest for liquid–liquid catalysis. We also synthesize soft composites in solid, liquid and gas combinations that have previously not been shown, including actuator materials with temperature-tunable microscale pores. We further demonstrate the potential of this method for constructing 3D materials that mimic tissue with an unprecedented level of control, and for microencapsulating human cells at densities that address an unresolved challenge in cell therapy. The revelation that fluid–fluid interfacial energy can drive structure formation in micropillar scaffolds offers a scalable way of synthesizing soft composites, which may have applications in building materials that mimic biological tissue.

Development of porous high-entropy alloys by mechanical alloying and chemical de-alloying

ABSTRACT In this study, nanoporous high-entropy alloys (HEAs) were fabricated by chemically de-alloying aluminium atoms in mechanically alloyed HEAs. In addition, the effect of alloy composition, compositional uniformity, and porosity of the HEA precursors on the pore structures of the final HEA foams was investigated. Aluminium was successfully de-alloyed only for Ni-free HEAs because of the low mixing enthalpy of Ni and Al. For HEAs containing pre-existing microscale pores, aluminium atoms were readily de-alloyed because the pores opened pathways for NaOH, thereby resulting in hierarchical micro-nanoporous structures in the final foams. For denser HEAs with better compositional uniformity, homogeneous nanoporous structures were revealed in the final foams.

Synergistic enhanced catalysis of micro-reactor with nano MnO2/ZIF-8 immobilized in membrane pores by flowing synthesis

A catalytic membrane micro-reactor (CMMR) with nano MnO2/ZIF-8 immobilized in membrane pores has been fabricated by flowing synthesis and formaldehyde degradation was used to test its catalytic performance. The CMMR with deep-permeation nano structure (DPNS) has good stability, uniform nano MnO2/ZIF-8 dispersion and higher loading capacity. The MnO2 coated on the surface of nano ZIF-8 with the size in the range of 100–150 nm was obtained. The contact between formaldehyde and MnO2 is enhanced by the effect of even disperse of membrane pores. The enhanced mass transfer can be achieved in the micro-scale pores of the membrane by the confined space effect. A higher amount of MnO2 loading and higher formaldehyde absorption rate can be achieved by the effect of ZIF-8 in membrane pores. The formaldehyde degradation rate was increased from 82.6% to 94.0%, if the MnO2 loading capacity was increased from 98 mg g−1 to 344 mg g−1.

Preparation of porous graphene nanosheets/carbon nanotube/polyvinylidene fluoride (GNS/CNT/PVDF) composites for high microwave absorption in X-band

With the rapid development of electronic devices, it is urgent to design and fabricate lightweight and effective electromagnetic absorption materials. Here, the graphene nanosheets/carbon nanotube/poly(vinylidene fluoride) (GNS/CNT/PVDF) composites with three-dimensional interconnected hierarchically porous networks have been successfully prepared via a facile solution mixing and followed by phase inversion method. The specific hierarchically porous structure in the composites possesses interconnected pores with various sizes. The open micro-scale pores on the top side give much smaller permittivity, which makes it less resistive to the incident microwave in a wide frequency range and is advantageous for multiple reflection and scattering of electromagnetic waves (EMW). The relatively smooth and dense bottom prevents EMW passing through the composites, which endows the prepared composites with a high EMW absorption. The as-prepared porous composites with 3.5 mm thickness exhibit a maximum absorption value of as high as − 32.7 dB at 11.50 GHz and display an ultra-wide efficient absorption bandwidth (entire X-band). Therefore, our work sheds light on a feasible strategy for designing and fabricating high-efficient EMW absorption materials.

Quartz types, silica sources and their implications for porosity evolution and rock mechanics in the Paleozoic Longmaxi Formation shale, Sichuan Basin

Quartz is a common mineral in mudrocks, displays variable forms and can have multiple origins. Consequently, the form and source of quartz in mudrocks may have a distinct impact on porosity evolution and rock mechanics such as brittleness. In this study, 51 shale samples from both the Lower and Upper parts of the Longmaxi Formation in the Sichuan Basin of China were collected for geochemical, mineralogical and elemental analyses, microscopic observation, porosity characterization, as well as rock mechanics testing, in order to better understand the quartz types, the sources of the silica, and their impacts on porosity evolution and rock mechanical behavior. Optical microscopy and field emission-scanning electron microscopy (FE-SEM) with energy dispersive spectroscopy (EDS) were applied to describe the crystal morphology and investigate the types and silica sources of quartz and their associated pores. Images from both methods reveal several forms of quartz in the Longmaxi Shale, including terrigenous detrital quartz, organism skeletal quartz, quartz overgrowths, authigenic microquartz and quartz veins. Furthermore, the authigenic microquartz has three subcategories, namely clay matrix-dispersed, euhedral and amorphous. The distinguishing criteria include crystalline morphology, luminescence, grain size and forming stage (including the stage of deposition and different periods of the diagenesis progress). Geochemical proxies, such as an Al–Fe–Mn ternary diagram, negative correlations of Zr vs. SiO2, and positive correlations of TOC vs. excess Si, indicate a substantial contribution of biogenic silica to the total silica in the Lower Longmaxi Formation. All possible pores associated with quartz are systematically described and classified into 3 types and 8 subtypes, notably dissolution pores, organism skeletal cavity pores, crystal defect pores, pores between quartz grains, grains contact micro-fractures, shrinkage micro-fractures and quartz filling micro-fractures. This study shows that the origin of the quartz may have implications for porosity evolution and rock mechanics. Positive correlations of surface area vs. excess Si indicate that biogenically derived forms of microquartz (including euhedral microquartz and amorphous microquartz cements) play a constructive role for micro-scale pore development. The correlation between high brittleness index and excess Si in the Lower Longmaxi Formation suggests that biogenic silica is the major cause of the brittleness.

Multi-stage infiltration of Na- and K-rich fluids from pegmatites at mid-crustal depths as revealed by feldspar replacement textures

In volcanic zones, geophysical observations have identified the presence of deep-seated fluids around intrusions in the mid-crust. However, the fluid compositions and mechanisms of fluid migration at high temperatures in the crust are still poorly understood. In this study, we investigated plagioclase alteration in mafic schists (clinopyroxene [Cpx] schist, hornblende [Hbl] schist, and actinolite [Act] schist) at the contact with a quartz diorite intrusion on Kinkasan Island, NE Japan. The quartz diorite consists of hornblende and plagioclase, and crystallized at 670–760 °C and 0.30–0.45 GPa. The quartz diorite contains abundant pegmatitic veins, which consist of plagioclase at their margins and K-feldspar + quartz ± garnet in their centers. Some pegmatitic veins cut the schistosity of the metamorphic rocks. In the metamorphic rocks, two stages of fluid-mediated alteration during cooling were recognized. The first stage of fluid infiltration (Stage I) was characterized by the formation of a reaction zone around pegmatitic dikes in the Cpx schists. The Cpx was altered to hornblende (Hbl) and Ca-plagioclase (An83–95) was altered to Na-plagioclase (An36–67). The replacement proceeded along the grain boundaries of plagioclase and clinopyroxene. The second stage (Stage II) resulted in the formation of K-feldspar veins and replacement of plagioclase (An35–57) by K-feldspar (An0Ab1Or99) and albite (An2Ab95Or3–An12Ab87Or1) in the Act and Hbl schists, and the latter were probably derived from the Cpx schists. Assuming the pressure was the same as the crystallization of the quartz diorite intrusion, the alteration temperatures were estimated as 690–730 °C for Stage I and 400–570 °C for Stage II. Mass balance considerations with assumptions of the volume conservation during the replacements of plagioclase and clinopyroxene/amphibole grains indicate the Cpx schists gained Na and H2O and lost Ca in Stage I, and the Act schists gained K and Si and lost Al and Ca at almost constant Na in Stage II. This indicates that the fluid composition changed from Na- to K-rich during cooling. During the Stage II alteration, when ~45% of the plagioclase grains were altered, significant nano- to micro-scale pores were generated in plagioclase, which produced a porosity of ~3.0%–3.5% in the plagioclase and increased the whole-rock porosity by 1.3% ± 0.2%. These pores are now isolated, irregularly shaped, and occur preferentially along the replacement front, suggesting that the pores migrated during or after replacement. The altered zone in plagioclase developed from trans-granular microcracks rather than grain boundaries. Our results suggest that infiltration of K-rich fluids could be self-promoting, with such fluids forming their own pathways via dissolution and precipitation processes during plagioclase replacement. Given that plagioclase is the dominant mineral in various rock types in the mid-crust, reaction-induced porosity networks in plagioclase could be the dominant fluid pathway at mid-crustal depths. The nature of this porosity and fluid migration are potentially controlled by temperature and/or the composition of the fluids.

Monovalent Cation-Induced Rock-Fluid Interactions in Saline Aquifers

Deep saline aquifers are suitable reservoirs for long-term storage and mitigation of CO2 emissions into the atmosphere. Injection and dissolution of CO2 in the formation brine lead to pH reduction of the reservoir fluid. The low pH environment accompanied with high pressure and high temperature (HPHT) conditions typical of deep saline aquifers trigger rock dissolution. Ion type can affect the amount of rock dissolution which in turn will impact the micro-scale pore structure of formation rock. Although formation brines consist of ions with different types, only a few studies have focused on the impact of this parameter on mineral dissolution. Therefore, this research aims to improve our understanding of ion-induced rock dissolution after CO2 injection. In this work, two batch experiments were conducted to compare the effect of Na+ and K+ on the extent of CO2-saturated brine reactivity in contact with a rock sample. Regarding the effect of monovalent ions, the existence of Na+ ion resulted in greater chemical rock-fluid interactions in comparison with K+ ion which can be related to the smaller radii of Na+ ion. Results of this study can aid in selecting more suitable saline aquifers for CO2 storage and more accurate long-term predictions from geochemical modelling.

Multifunctional cementitious composites with integrated self-sensing and hydrophobic capacities toward smart structural health monitoring

In this study, multifunctional cementitious composites with integrated self-sensing and hydrophobicity capacities were developed and investigated using conductive graphene nanoplate (GNP) and silicone hydrophobic powder (SHP). The mechanical properties, permeability, water contact angle, microstructure and piezoresistivity were studied and compared under different contents of GNP and SHP. The highest compressive and flexural strengths with 1% SHP and 2% GNP reached 62.6 MPa and 8.9 MPa, respectively. The water absorption significantly was decreased with the content of SHP, but was minorly affected by GNP. The water contact angle firstly increased but then decreased with the dosages of GNP and SHP. SHP and GNP could reduce the microscale pores and enhance the density of microstructures. The piezoresistivity under compression firstly exhibited low gauge factor, but then gradually increased to a constant value under high-stress magnitude. Moreover, compared to the conventional cement-based sensors, this piezoresistive cementitious composites containing SHP and GNP as novel cement-based sensors are less sensitive to water content and humidity. The outcomes can provide an insight into promoting the application of multifunctional cement-based sensors toward structural health monitoring under various ambient conditions.

Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

Tight sandstone reservoirs have small pore throat sizes and complex pore structures. Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, based on casting thin sections, nuclear magnetic resonance experiments, and modal analysis of pore size distribution characteristics, the Chang 6 tight sandstone reservoir in the study area can be divided into two types: wide bimodal mode reservoirs and asymmetric bimodal mode reservoirs. Based on the information entropy theory, the concept of “the entropy of microscale pore throats” is proposed to characterize the microscale pore throat differentiation of different reservoirs, and its influence on the distribution of movable fluid is discussed. There were significant differences in the entropy of the pore throat radius at different scales, which were mainly shown as follows: the entropy of the pore throat radius of 0.01~0.1 μm, &gt;0.1 μm, and &lt;0.01 μm decreased successively; that is, the complexity of the pore throat structure decreased successively. The correlation between the number of movable fluid occurrences on different scales of pore throats and the entropy of microscale pore throats in different reservoirs is also different, which is mainly shown as follows: in the intervals of &gt;0.1 μm and 0.01~0.1 μm, the positive correlation between the occurrence quantity of movable fluid in the wide bimodal mode reservoir is better than that in the asymmetric bimodal mode reservoir. However, there was a negative correlation between the entropy of the pore throat radius and the number of fluid occurrences in the two types of reservoirs in the pore throat radius of &lt;0.01 μm. Therefore, pore throats of &gt;0.1 μm and 0.01~0.1 μm play a controlling role in studying the complexity of the microscopic pore throat structure and the distribution of movable fluid in the Chang 6 tight sandstone reservoir. The above results deepen the understanding of the pore throat structure of tight sandstone reservoirs and present guiding significance for classification evaluation, quantitative characterization, and efficient development of tight sandstone reservoirs.

Microscale Mineral and Pore Structure Characterization of the Low‐Permeability Sandstone in the Ordos Basin, China

Given the insufficient understanding of the characteristics and controlling factors of the low‐permeability sandstone reservoir in the Heshui area, the Ordos Basin, the present study examined the microscale mineral and pore structure of Chang 2 reservoir. It analyzed its major controlling factors using a series of methods, including imaging and indirect methods. The results show that the rocks of Chang 2 reservoir in the study area are dominated by lithic arkose and feldspathic detritus quartz sandstone. The reservoir space develops intragranular pores, feldspar dissolved pores, lithic dissolved pores, and intercrystallite pores. Microcracks can occasionally be found. The average porosity is 10.5%, and the average permeability is 2.2 mD, featuring a low‐porosity‐ultralow‐permeability reservoir. During the reservoir development, traps formed by small‐scale nose‐shaped uplifts resulting from the tectonic effects provide opportunities for good reservoir space. Sedimentation and diagenetic processes control the degree of development and direction of the evolution of reservoir porosity to a certain degree. Multisegment capillary pressure curve and long missing zone were corresponding to relatively good pore‐throat structures. Illite was the predominant diagenetic clay minerals that determine the reservoir quality. These three effects all contribute to the overall development of the reservoir.

Influence of clay minerals and cementation on pore throat of tight sandstone gas reservoir in the eastern Ordos Basin, China

The distribution characteristics of pore throat play a vital role in the exploration and development of tight sandstone reservoirs. Based on the thin sections and scanning electron microscopy, this paper studied the petrological characteristics of tight sandstone reservoirs the Permian Shihezi Formation and the Shanxi Formation in the Ordos Basin. The micro-scale and nano-scale pore throat parameters of the target samples were quantitatively analyzed by high-pressure mercury injection experiments. At the same time, the content of clay minerals and various cement in the samples was extracted and obtained by X-ray diffraction to explore the effects of the clay minerals and cementation on the pore-throat. The results showed that the micro-scale pore space of the tight sandstone in the study area was mainly composed of residual intergranular pores and dissolution pores. The nano-scale pore throat consisted with the intercrystalline pore of clay minerals, dissolution pores of fake matrix, micro-crack and the intergranular pore of quartz overgrowth, the intergranular pore of quartz grains, which correspond to four types of mercury injection curves. According to XRD data and mercury injection results, the evolution of the tight sandstone pore-throat is mainly controlled by kaolinite, illite, and the companion product: siliceous cement. Chlorite and calcareous cement have little effect on reservoir porosity, average pore throat radius and permeability. Two evolution models of the pore-throat of tight sandstones in which clay minerals and cement as the dominant factors were established.

Pore-Scale Movability Evaluation for Tight Oil Enhanced Oil Recovery Methods Based on Miniature Core Test and Digital Core Construction

The movability of micro-remaining oil in microscale pores in tight reservoirs directly affects the recoverability of a reservoir fluid. Currently, core displacement and digital cores have been appl...

Blood clots and tissue regeneration of 3D printed dual scale porous polymeric scaffolds

Blood clotting on implanted porous scaffolds has been suggested to be key to tissue regeneration. We recently reported a new type of 3D printed macroscale porous scaffolds with intra-strut microscale pores, that supported strong bone regeneration in vivo. Yet it remains unclear the effects of this microscale porosity on blood clots. Here, we studied the morphology of the blood clots at the interface with the scaffolds in vitro and analysed the scaffold-tissue interface in vivo. We then suggested a novel role of the scaffold’s microscale pores and surface roughness in supporting bone formation via their effects on blood infiltration and clotting.

Quantitative relationship between pore size distribution and compressive strength of cementitious materials

Cementitious materials have complex pore structure, which has a significant impact on material properties. The present paper aims to determine the quantitative relationship between pore size distribution and compressive strength of cementitious materials. An influence function is proposed to describe the influence of pore size on strength, based on which an integral model of compressive strength is established. A total of 11 sets of mortar specimens with wide differences in pore size distribution were prepared with the virtual pore method to verify the influence function and the strength model. The influence function indicates that the effect of pores per unit volume on strength increases with the increase of pore size. The effect increases slowly at small pore size and increases significantly at large pore size like microscale pores. The influence of porosity on strength can be determined quantitatively with the proposed influence function when the pore size distribution is obtained, which further gives the predicted strength. It is indicated that microscale pores have a significant impact on the material strength, so the existence of these pores should be avoided to improve material strength.