Fractal Dimension Of Pore Structure Research Articles

Short-term interactions between Longmaxi shale and carbon dioxide-based fracturing fluids

The shale is a dense quarried rock material containing abundant shale oil/gas. Extracting shale gas usually requires fracturing the rock formation to speed up gas desorption and migration. Supercritical carbon dioxide fracturing, as an environmentally friendly and waterless fracturing technique of reservoir stimulation, gains increasing recognition in commercial exploitation of shale oil and gas. However, there is insufficient understanding on the interaction between carbon dioxide-based fracturing fluids and shale, as well as its influence on the mechanical parameters of shale, which are pivotal for determining injection parameters and forming the fracture network. This study focuses on the injection of carbon dioxide-based fracturing fluids to enhance shale gas extraction and carbon dioxide sequestration. Simulation tests of injection were conducted to investigate the influence of different fracturing fluids (deionized water, gaseous/supercritical carbon dioxide, gaseous/supercritical carbon dioxide mixed with brine) injected into shale reservoirs on the microstructure and mechanical properties of shale after short-term physicochemical interaction. This article adopts research methods such as uniaxial compression and uniaxial tensile mechanical experiments based on acoustic emission monitoring and various physical characterizations such as scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectrometer, etc. Results show that following treatment with different carbon dioxide-based fluids, the uniaxial tensile/compressive strength, elastic modulus, fractal dimension of pore structure, and the brittleness index of shale exhibit varying degrees of decrease compared to those of dry untreated shale samples. After interacting with different carbon dioxide-based fracturing fluids, the mechanical parameters and brittleness index of shale decrease more significantly than that of the others as the addition of brine. This study shows that the water in carbon dioxide-based fracturing fluids is a controlling factor affecting the elastic modulus of shale. Additionally, the ductility of the shale increases and the acoustic emission emitting lag due to the coupling effects of brine and carbon dioxide. The change law of the elemental and mineral composition of the shale is consistent with the mechanical strength; and the change of element content and mineral composition is the most significant. Compared to gaseous carbon dioxide, the supercritical carbon dioxide has a greater impact on mineral composition of the shale. The change of mechanical strength and microstructure evolution mechanism caused by the short-term interactions between the shale and fracturing fluids provide theoretical references and implications for the determination of injection parameters and permeability transformation of the Longmaxi shale reservoirs.

Simulation of the effects of nanopores at different scales on the wettability of coal

The structural difference of nanopores at different scales in coal is one of the important factors that affect the wettability of coal. Therefore, it is necessary to determine influences of nanopores at different scales in coal on the wettability thereof from the perspective of molecular structure. Taking coal samples collected from Pingdingshan (PDS), Hebi (HB), Xiegou (XG), and Changping (CP) as research objects, the nanopore combination types of the interface were divided by using Materials Studio (MS) molecular simulation software and Image Pro Plus (IPP) image processing software, fractal theory and wettability dynamic simulation method, and the fractal characteristics of different nanopore combination types and the wetting angle change characteristics of active water were analyzed. The effects of total porosity and fractal dimension of pore structure on wettability of nanopores were discussed. The results show that the nanopore combinations in coal can be divided into three types according to the diameter of water molecules: those separately dominated by diffusion pores, adsorption-diffusion pores, and adsorption pores. As the diameter of dominant pores decreases, the fractal dimension decreases and the structure becomes increasingly simple. The wetting angle of active water in diffusion pores changes as follows: it rapidly decreases at first, then tends to stabilizes, before increasing slightly; that in adsorption-diffusion pores changes in this way: it rapidly decreases after transient fluctuations, then basically stabilizes, and finally slightly increases; that in adsorption pores changes as follows: it fluctuates for a long period, then decreases with fluctuations, and finally basically stabilizes. As the total porosity of nanopores increases, the wetting angle decreases linearly. If the porosity is similar, the negative influence of fractal dimension on the wettability of coal interfaces by active water increases as the scale of dominant pores in pore combinations decreases.

Pore structure characteristics of coral reef limestone: a combined polarizing microscope and CT scanning study

Coral reef limestone is a special class of geological medium formed through long-term deposition following the death of reef-building coral groups. Because it retains the skeletal structure of marine organisms during its formation, its pore structure is hyper-developed and complex. Deciphering the pore structure of the coral reef limestone is important because it is closely related to its macroscopic physical and mechanical properties. This study conducted a comprehensive analysis of the pore structure features of two types of coral reef limestone collected from the construction site of a nuclear power station located in the South China Sea using a combination of polarizing microscopy and CT scanning technologies. The fractal dimension of the pore structure of the treated reef limestone image was calculated, and the pore structure characteristics were statistically analyzed by considering several parameters including porosity, pore size, pore equivalent radius, shape factor, etc. In addition, the directional feature of the pore structure was explored. The results show that the improved watershed segmentation algorithm can accurately segment the pore structure of reef limestone images; both coral reef limestone specimens are loose of high porosity; the fractal dimension of pore structure lay between 1.58∼1.75, indicative of a high self-similarity; the pore size of the two coral reef limestone specimens is quite different, and the distribution of equivalent pore radius conforms to the normal distribution law; the pore structure of the two samples had obvious directionality, which can be quantified using a directional tensor. This study sheds light on future investigations linking the microscopic structure and macroscopic properties of coral reef limestones.

Dynamic Evolution of Coal Pore-Fracture Structure and Its Fractal Characteristics under the Action of Salty Solution

The instability and failure of coal pillars is one of the important factors leading to the catastrophic consequences of coal mine goaf collapse. Coal mine water has the characteristics of high salinity. Long-term mine water erosion can easily deform the coal pillar structure, eventually leading to instability and damage. This study carried out tests on coal samples soaked in salt solutions with different concentrations, and the nuclear magnetic resonance (NMR) method was used to obtain the dynamic evolution of the pore-fracture structure of coal. On the basis of fractal theory, the changes in fractal dimension of pore structure during the soaking process were discussed. The damage variable based on the pore fractal dimension was defined and the evolution relationship between the damage variable and immersion time was characterized. The findings demonstrated that the porosity change rate has an exponentially increasing relationship with the immersion time, and with the increasement of concentration of salt solution, the porosity change rate also shows increasing trends. The number of seepage pores and total pores increased with the immersion time. While, with the extension of soaking time, the number of adsorption pores first increased and then decreased. The connectivity between pores was enhanced. The relationship between the fractal dimension and the immersion time is linearly decreasing. The damage variable showed an increasing trend with the immersion time. As the concentration of salt solution increased, the damage of coal increased. The research results are of great significance for rationally evaluating the stability of coal pillars and ensuring the safe operation of underground engineering.

Pore structure characteristics of admixture shotcrete and its quantitative relationship with mechanical properties in high geothermal environment

The high geothermal environment during tunnel construction leads to the abnormal porosity and decreased mechanical properties of shotcrete, but its degradation mechanism is still unclear. The compressive strength, flexural strength, and stress-strain curve of shotcrete with 10 %–30 % fly ash (FA) and slag (SA) with curing temperature of 80 °C and curing humidity of 55 ± 2 % were studied. The types and microstructure of hydration products were researched through XRD and SEM. Different from the traditional method of calculating the fractal dimension of the whole pore size measured by MIP, the partition fractal dimension based on pore diameter classification is innovatively adopt to reflect the pore structure surface area, pore content, and tortuosity. Moreover, the quantitative relationship between the fractal dimension of pore structure and mechanical properties was analyzed by rough set theory. The strength of shotcrete with FA decreases by 12.9 %–13.1 % under 80 °C curing. As a contrast with 10 %–30 % SA to enhance its 3.2 %–13.1 %. Both FA and SA can increase the flexural strength of shotcrete by 1.2 %–33.3 %. The strain of shotcrete with FA or SA is the largest when the content is 20 %, but the ultimate strain decreases with the extension of curing age. The main pore structure type of shotcrete with FA and SA is transition pore (10 nm ∼ 100 nm), accounting for 48.86 % ∼ 57.28 % and 54.52 % ∼ 62.03 % of the total pore volume, and the addition of 20 % FA significantly reduces the large pore (≥1000 nm) of shotcrete. The addition of FA and SA makes the surface of gel pores in shotcrete smoother, and makes the spatial structure of gel pores and large pore in shotcrete more complicated. The incorporation of FA and SA reduced the tortuosity of capillary pores (100 nm ∼ 1000 nm), but increased the tortuosity of gel pores (<10 nm). The pore volume of capillary and transition pores and the surface area of capillary pores have significant effects on the strength of shotcrete. However, the tortuosity of pores has little effect on the strength of shotcrete.

A new mesoscopic calculation model of chloride ion erosion in recycled coarse aggregate concrete (RAC): Characteristic fractal dimension of pore structure and service life prediction

This research investigates the influence of water-cement ratio and recycled aggregate content on the chlorine erosion resistance of RAC by conducting a combination of experimental and theoretical analysis. In addition, a mathematical equation is developed to represent the chloride ion transport mechanism in RAC, taking into account fluid mechanics, energy conservation, and pore structure evolution characteristics. Furthermore, mathematical analysis and modeling are used to forecast the life of the chloride ion erosion process. The results show that both the recycled coarse aggregate replacement rate and the water-cement ratio adversely affect the chloride erosion resistance of RAC. The chloride diffusion coefficient model based on pore structure characteristic parameters exhibits high prediction accuracy. This model helps increase the use of recycled aggregates and fosters the growth of the circular economy in the construction industry sector by offering a theoretical foundation for evaluating and maintaining the durability of RAC.

Effect of nano admixtures on the engineering properties and microstructure of sulphoaluminate cement mortar at −10 °C

The traditional cement-based cementitious materials cannot hydrate at −10 °C, and the sulfoaluminate cement can hydrate, but the cement slurry has poor properties and low strength. Three kinds of nano admixtures (silica fume, nano-SiO2, nano-CaCO3) were selected as modified materials, and the effect of nano admixtures on the fluidity, strength, internal temperature, micro-morphology, mineral composition and pore structure of sulphoaluminate cement mortar were studied under the condition of mixing and curing of cooled materials at −10 °C. The results show that the fluidity, compressive strength and flexural strength of mortar increase first and then decrease with admixture content. When the content of silica fume, nano-SiO2 and nano-CaCO3 is 3 %, 0.5 % and 0.5 % respectively, the fluidity and strength of mortar are the maximum. With the optimum content of three kinds of nano admixtures, nano-SiO2 has the best improvement on the strength and internal temperature of mortar. The hydration of sulphoaluminate cement can continue at −10 °C. At the age of 1 d, ettringite is yielded in the mortar. After the addition of nano admixtures, the amount, characteristic diffraction peak and diffraction intensity of ettringite in mortar increase. The nano admixtures can optimize the pore structure of mortar with the age of 1 d. The fractal dimension of pore structure of mortar with 0.5% nano-SiO2 is the minimum.

Characterization, factors, and fractal dimension of pore structure of fly ash-based geopolymers

Fly ash-based geopolymer is a new cementitious material with environmentally friendly characteristics. Generally, the mechanical properties of cementitious materials are influenced by their pore structure. The variation in the pore structural characteristics of the geopolymers with various influencing factors was investigated in this study. A smaller activator modulus and liquid-solid ratio lead to a finer pore structure, while higher activator concentrations also result in a finer pore structure. However, the densification of pore structure does not follow a monotonic relationship with the conserving temperature. Increasing the conserving temperature within a certain range decreases the most probable pore diameter and porosity. Nevertheless, excessive temperature increase has the opposite effect. Furthermore, the fractal dimension was introduced to characterize the pore structure comprehensively. The results show that a lower pore volume, a larger pore-specific surface area, and a smaller most probable pore diameter contribute to increasing pore surface fractal dimension. Further, compared to porosity, the microporous pore surface fractal dimension shows a better linear correlation with compressive strength.

Study on the reduction of Fe2O3 pellets by CO-CO2 and H2-H2O: Reaction kinetics and pore network model

The steel industry contributes to creating an environmentally friendly society by providing high-quality steel and working to develop low-carbon processes. Using hydrogen produced from renewable energy to replace part of coke in blast furnaces is one of the measures to reduce fossil carbon dioxide emissions in the process of steelmaking. In this paper, a series of reduction experiments of Fe2O3 pellets at different temperatures were carried out under three conditions of hydrogen-rich in blast furnace. The variation law between reduction degree and apparent activation energy was calculated. The result shows that when the reduction degree reaches 11% and 70%, the apparent activation energy reaches the peak, which are 38.9 kJ/mol and 19.5 kJ/mol, respectively. This suggests that the reduction process is affected by two or more mechanisms. Then, on the basis of the typical single interface reaction kinetics model, the multistep reduction kinetics model of hydrogen-rich reduction Fe2O3 pellets was established. In addition, based on the results of industrial computerized tomography (CT) analysis, the three-dimensional pore network model and velocity model of Fe2O3 pellets after reduction were established. The coupling relationship between the fractal dimension of pellet pores and reduction atmosphere was studied by introducing fractal theory. Under hydrogen-rich reduction condition, the volume fractal dimension of pore structure of Fe2O3 pellets increases from 2.41 to 2.58. Therefore, the pore structure formed by hydrogen-rich reduction is conducive to the diffusion of reducing gas in the pellet, so as to improve the reduction degree of pellet.

How pore structure evolves in shale gas extraction: A new fractal model

The reservoir can be divided into four components with different properties: inorganic matrix, hydraulic fracture, natural fracture and kerogen according to the internal structure characteristics and the natural gas migration mode after hydraulic fracturing. Previous studies usually focus on the relationship between reservoir porosity and permeability, but ignore the influence of reservoir microstructure on gas production. The microstructure of different reservoir components can be described by corresponding fractal dimensions. The structure of fractures can be characterized by fractal dimension of fractures and the fractal dimension of pores can characterize the pore structure of inorganic matrix. Considering the complexity of mass transfer between components and structural deformation, in order to describe the evolution of reservoir microstructure and the influence of various factors on gas production, a fully coupled multi-scale fractal model is established. To verify that the model is reliable, the simulation results contrast with the conclusions of field tests. The effects of adsorption parameters, initial diffusion coefficient and compressibility coefficient on gas production and pore structure evolution were studied. The results show that:(1) when the adsorption constant decreases, the variation of the fractal dimension of pore structure becomes more obvious, and the shale reservoir's gas production and pore structure are most sensitive to the volume constant; (2) the deformation of pore structure increases with the increase of effective diffusion coefficient; (3) the change of compressibility of a single medium only has a major impact on the evolution of its own structure.

Study on characterization technology of porosity and fractal dimension of micro-arc oxidation coating

Abstract The porosity of the micro-arc oxidation coating of pure titanium was assessed through the utilization of Mercury intrusion porosimetry (MIP). The porosity values were subsequently adjusted by accounting for the proportion of coating volume, resulting in a more precise determination of the coating’s porosity. Additionally, the fractal dimension of the pore structure was determined through the application of a linear regression equation utilizing the Mercury intrusion data. The findings indicate that the observed numerical dispersion from image metohd is substantial, with a range of 34.9% between the minimum and maximum values. This suggests that the precision and validity of the porosity outcomes derived from this approach are inadequate; The MIP is capable of determining both the porosity, average pore size and pore size distribution of the sample, while also mitigating the impact of the matrix through test result correction, thereby yielding precise porosity values. Additionally, the results of the verification experiment demonstrate a positive correlation between the porosity alteration of the MIP and oxidation duration, thereby affirming the reliability of the test outcomes; Through the analysis of pressure, pore size, cumulative Mercury intrude volume, and incremental Mercury intrude volume data obtained from MIP, the fractal dimension of the coating’s pore structure then be determined. Research showed that as the oxidation time increases, the pore fractal dimension of the MAO coating gradually expands within a narrow range, from 2.57 and finally stabilized at 2.77, indicating a gradual increase in pore structure complexity.

Microwave heating efficiency and frost resistance of concrete modified with powder absorbing materials

Microwave deicing technology has the advantages of economy, environmental protection, cleaning, energy saving and so on, and it has future prospects in snow melting and deicing of concrete pavement. In order to improve the microwave heating efficiency of concrete without reducing its practicability, Fe3O4 modified concrete, SiC modified concrete and graphite modified concrete are taken as research subjects. The effects of 3 kinds of powder absorbing materials (PAM: Fe3O4, SiC and graphite) on microwave heating efficiency and frost resistance of concrete are studied by microwave heating test and freeze–thaw cycles test. And the micromechanism of the effect of PAM on the frost resistance of concrete are interpreted using SEM and MIP techniques. The results show that the microwave heating efficiency of concrete increases after adding PAM, the addition of Fe3O4 and graphite reduce the frost resistance of concrete, and the addition of SiC improves the frost resistance of concrete, and the optimal content of SiC is 10%. The PAM can fill macropores but decrease the bonding properties of cement paste. The pore size, percentages of less-harmful pore and harmful pore of concrete increase after freeze–thaw cycles. The pore structure of concrete shows significant fractal features before or after freeze–thaw cycles. And after freeze–thaw cycles, the fractal dimension of pore structure of concrete increases and the pore structure deteriorates.

Evolution Law of Micro-Pore Structure of Cement-Emulsified Asphalt Mortar Based on NMR

Cement emulsified asphalt mortar (CA) is widely used as the cushion of two types of ballastless track (CRTS I and CRTS II) in high-speed railways. Nowadays, the lack of durability of CA mortar has severely affected the quality of high-speed railways, failing to meet the requirements of sustainability. Since CA mortar is a kind of porous material, its performance can be significantly affected by its microstructures, which means that revealing the evolution law of its microstructures can provide the basis for improving its durability. Therefore, CA mortar species with different asphalt-cement ratio under different curing ages were prepared based on the requirements of CRTS II in this research and the pore structures were determined based on SEM and NMR methods. Then, a fractal model of CA mortar pore volume was proposed based on the concept of box fractal dimension, and the fractal dimension of pore volume was calculated. The relationship between fractal dimensions and mechanical property was analyzed based on Pearson correlation coefficient and regression analysis. The results suggested that the overall microstructure of CA mortar shows a loose porous space structure with cement hydration products being the continuous phase and asphalt being the dispersed phase. With the increase in A/C ratio, the hydration products produced by cement hydration decrease, and the total porosity and average porosity of CA mortar gradually increase due to the increase of asphalt hindering the hydration process of the cement. With the increase in curing age, the pore structure of CA mortar becomes more compact. However, the evolution law of CA mortar pore structure with age is not consistent under different A/C ratios due to the influence of asphalt. The pore structure of CA mortar was proved to have obvious fractal characteristics based on the concept of box fractal dimension and the experimental data of NMR. In addition, the correlation analysis proves that the fractal dimension of pore structure has an obvious positive correlation with the compressive and flexural strength, which suggests that the fractal dimension of pore volume can be a bridge for connecting the macro-property and micro-structures of CA mortar.

Strength Analysis of Cement Mortar with Carbon Nanotube Dispersion Based on Fractal Dimension of Pore Structure

Carbon nanotubes (CNTs) are considered among the ideal modifiers for cement-based materials. This is because CNTs can be used as a microfiber to compensate for the insufficient toughness of the cement matrix. However, the full dispersion of CNTs in cement paste is difficult to achieve, and the strength of cement material can be severely degraded by the high air-entraining property of CNT dispersion. To analyze the relationship between the gas entrainment by CNT dispersion and mortar strength, this study employed data obtained from strength and micropore structure tests of CNT dispersion-modified mortar. The fractal dimensions of the pore volume and pore surface, as well as the box-counting dimension of the pore structure, were determined according to the box-counting dimension method and Menger sponge model. The relationship between the fractal dimensions of the pore structure and mortar strength was investigated by gray correlation. The results showed that the complexity of the pore structure could be accurately reflected by fractal dimensions. The porosity values of mortar with 0.05% and 0.5% CNT content were 15.5% and 43.26%, respectively. Moreover, the gray correlation between the fractal dimension of the pore structure and strength of the CNT dispersion-modified mortar exceeded 0.95. This indicated that the pore volume distribution, roughness, and irregularity of the pore inner surface were the primary factors influencing the strength of CNT dispersion-modified mortar.

In-depth investigation of pore structure and fracture behavior of CAC bonded alumina-spinel castables treated at 110 ∼ 1600 °C

An in-depth investigation of pore structure evolution and corresponding fracture behavior of calcium aluminate cement (CAC) bonded alumina-spinel castables treated at 110–1600 °C has been carried out by taking the respective advantages of mercury intrusion and micro-CT scanning, wedge splitting test and acoustic emission, respectively. The results showed that the complexity of nano-sized and submicron-sized pores increased from 110 to 800 °C, and then decreased gradually from 800 to 1600 °C due to the dehydration of hydrates and formation of C12A7, CA, CA2, and CA6 phases. In comparison, the complexity of the pores above 1 μm increased with the ascent of treating temperatures. Consequently, the heat treatment resulted in deterioration of “toughness” owing to the vanish of majority of nano-sized and submicron-sized pores and the subsequent formation of strong ceramic bonding. The fractal dimension of pore structure presented positive correlation with “toughness” of castables, where higher fractal dimension standed for higher frature energy consumption within matrix caused by tortuous crack propagation paths.

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

Magnesium oxysulfate (MOS) cement is a typical eco-friendly cementitious material, which presents excellent performances. In this work, a novel multiscale modeling strategy is proposed to simulate the hydration and pore structure of MOS cement system. This work collected and evaluated the Gibbs free energy of formation for main hydrates and equilibrium constant of main reactions in MOS cement system based on a first principle calculation using Material Studio. Followingly, the equilibrium phase compositions of MOS cement system were simulated through PHREEQC to investigate the molar ratio dependence of equilibrium phase compositions. Results showed that large M (MgO/MgSO4) was beneficial for the formation of 5Mg(OH)2·MgSO4·7H2O (Phase 517) and large H (H2O/MgSO4) tended to decompose MOS cement paste and cause leaching. The microstructure-based method visualized the hydration status of MOS cement systems at initial and ultimate stages via MATLAB and the results showed that large M was significant to reduce porosity, and similar results for the case of small H. Fractal analysis confirms that fractal dimension of pore structure (Df) was significantly decreased after the hydration of MOS and was positively correlated to the porosity of the paste. In addition, it can be referred that large M and small H were beneficial for modifying the microstructure of MOS paste by decreasing the value of Df.

Experimental Investigation on Microstructure and Permeability of Thermally Treated Beishan Granite

Abstract A good understanding of thermal effect on physical properties (especially the permeability) of host rock is essential for a high-level radioactive waste (HLW) deep geological repository. In this study, we carried out comprehensive tests (permeability measurement, p-wave velocity measurement, mercury intrusion test, and nuclear magnetic resonance [NMR]) to study the macroproperties and microstructures of Beishan granite after different temperature treatments. We found the permeability decreased after treatment at 300°C then increased sharply with increasing temperature as temperature exceeded 400°C. Results from the mercury intrusion test and NMR measurement showed that the pore size and pore volume both decreased for granite after being treated at 300°C, which indicated that pores closured around 300°C for Beishan granite. From 400°C upward, the pore size and volume gradually increased with temperature. Based on the relationship of measured T2 data from NMR with Pc curves from mercury intrusion measurement, the synthesized Pc curves was constructed using NMR-measured data of thermally treated Beishan granite. The fractal dimension of pore structure was studied based on pore size distribution from NMR data. Consistent with the evolution of permeability, the fractal dimension decreased for granite after treatment at 300°C, then increased with temperature from 300°C to 700°C. Because the fractal dimension of thermally treated granite is effective in characterizing the variation of pore structures, a semiempirical formula is proposed to predict the permeability using the fractal dimension and porosity.

Fractal characteristics of pore networks and sealing capacity of Ordovician carbonate cap rocks: A case study based on outcrop analogues from the Tarim Basin, China

Understanding and predicting the main controls on the sealing capacity of carbonate cap rocks is of great significance for ultradeep carbonate reservoir exploration and production. This study focuses on revealing the pore networks and sealing capacity of the Ordovician carbonate cap rocks in the Tarim Basin by analyzing samples from outcrop analogues using optical and scanning electron microscopy and a combination of mercury intrusion capillary pressure and nitrogen gas adsorption. Three classes of cap rocks are defined here according to their pore-throat structure, fractal dimension, and sealing capacity. These carbonate cap rocks are dominated by limestones and dolomitic limestones. Four pore types are identified: microfractures, intragranular, intercrystalline, and intracrystalline. Six pore structure types show multiscale variability from macropores to micropores. The pore structures present multiple fractal behaviors, with fractal dimensions showing an increasing trend as the pore diameter decreases. The cover coefficient, a parameter that allows characterization of the caprock sealing performance, shows an increasing trend along with increasing the fractal dimension of pore structure. The average cover coefficients of six pore structure types not only show good correlations (either exponential or linear) with certain fractal dimensions, but they also demonstrate a strong positive correlation with the average fractal dimension. These results suggest that the sealing capacity of the studied rocks increases with increasing fractal dimension. The sealing performance of cap rocks significantly decreases with an increasing amount of macropores. This work provides a relevant case study for further understanding of pore structures and sealing capacity of carbonate cap rocks.

Study on effect of mechanical sand on mechanical properties and fractal characteristics of mortar pore structure

The influence of stone powder content, fly ash and other factors on mechanical properties, pore structure and fractal dimension of machine-made sand mortar were studied, and the relationship between fractal dimension and mechanical properties of mortar was explored. The research shows that with the increase of the content of stone powder, the mechanical properties of mortar and the fractal dimension of pore structure of different sizes increase; the porosity and average pore size of the mortar decrease, and the ternary of cement-fly ash-stone powder The micro-particle system can effectively optimize the pore structure distribution of the mortar; the fractal dimension of the mortar using ordinary river sand is significantly smaller than that of machine-made sand under the same conditions; with the increase of the fractal dimension of the pore structure, the compressive strength and flexural strength of the mortar continue to increase Large, the fractal dimension and the macroscopic mechanical properties of the mortar show a good correlation.

Segmentation of multi-coal seam pore structure in single well profile and its sedimentary control: a case study of Well Y1 in Panguan syncline, western Guizhou, China

The pore structure of coal reservoirs is crucial for the occurrence and production of coalbed methane (CBM). Taking as an example the upper Permian coal-bearing strata profile of Well Y1 in Panguan syncline of western Guizhou, mercury intrusion porosimetry (MIP) and low-temperature N2 adsorption/desorption (LT-N2GA) experiments were carried out on samples from six main coal seams. Hysteresis coefficients of MIP and LT-N2GA were proposed. Fractal dimension of pore structure of each coal seam was calculated. The segmentation of pore structure of multi-coal seams was found. We found the total pore volume (TPV) and specific surface area (SSA) of coal were increased and then decreased as the increase of coal seam buried depth, which is characterized by two-segment distribution. The upper segment included the 7#, 10#, and 12# coal seams, whereas the lower segment contained the 18#, 19#, and 24# coal seams. The TPV, SSA, and MIP hysteresis coefficients and fractal dimension of seepage pore of the upper segment coal seams are larger than those of lower segment coal seams on the whole, while the LT-N2GA hysteresis coefficient, fractal dimension of adsorption pore, and fractal dimension of high-pressure stage of the upper segment are smaller than those of the lower segment. The coal seams in upper segment have more open pores, while the coal seams in the lower segment have more fine neck bottle pores or ink bottle pores. Taken together, these data demonstrated that the coal seams in the upper segment have higher adsorption and seepage capacity, and are more favorable for CBM development. The fundamental reason for the two-segment variation of TPV and SSA of six main coal seams is the symmetry of sedimentary facies in coal-bearing strata; moreover, the ash yield controls the TPV and SSA of coal seams, and the ratio of vitrinite to inertinite (V/I) controls the development of pores.