Pore Size Distribution Measurements Research Articles

Estimation of mass transfer rate and primary drying times during freeze-drying of frozen maltodextrin solutions based on x-ray μ-computed tomography measurements of pore size distributions

The study presents a method to estimate the mass transfer rate during primary drying based on μ-computed tomographic measurements of a freeze-dried cake. The study was carried out in a defined setup in a lyomicroscope and confined geometry in which freezing occurred under homogeneous nucleation, and drying under mass-transfer-limited conditions. Pore size distribution, effective diffusivity, and primary drying rates of maltodextrin solutions at different weight concentrations (5%, 10%, and 20% (w/w)) and different cooling rates were determined. Furthermore, the effect of annealing treatment on primary drying rate was studied. Two different annealing treatments were tested, one for 90 min at −10 °C and another for 180 min at −5 °C. It was shown that solid concentration and annealing above Tg’ have the strongest impact on pore size and, subsequently, on primary drying rate. Therefore annealing represents a powerful tool to accelerate primary drying which is the most time-consuming step during lyophilisation.

Synthesis using natural functionalization of activated carbon from pumpkin peels for decolourization of aqueous methylene blue

In this study, a novel approach was applied for modification and functionalization of pumpkin peels (PP) derived carbon using natural beetroot extract. PP waste biomass was carbonized at 250 (AC250), 350 (AC350), 450 (AC450) and 550 °C (AC550) and used as adsorbent for the scavenging of methylene blue (MB). The adsorption results revealed that AC250 was the most efficient material. Thereafter, AC250 was further modified with different acids and natural beetroot extract to enhance the adsorption efficiency for MB removal. Modified and functionalized carbon materials were characterized to determine the functional groups, crystalline nature and surface morphology of adsorbents using Fourier Transformed Infra-Red spectroscopy, X-ray Diffraction and Scanning Electron Microscopy. The pore size distribution measurements by non-local density functional theory (NLDFT) revealed the presence of large number of mesopores in the beetroot activated carbon (BAC) with the BET specific surface area of 3.6 m2.g−1. The adsorption studies exhibited the highest adsorption (198.15 mg.g−1) for MB using 0.5 g.L−1 of adsorbent mass at 200 mg.L−1 MB concentration and 50 °C within 180 min. Reaction kinetics analysis of the experimental data revealed that adsorption followed pseudo second order kinetic model where BAC250 showed highest reaction rate constant value of 0.0095 and correlation coefficient value of 0.9992. The equilibrium data were tested by using Freundlich and Langmuir isotherm models. For both isotherms, the characteristic parameters were determined and the adsorption behaviour was found to fit well with the Langmuir isotherm model indicating monolayer adsorption of MB.

Nuclear magnetic resonance surface relaxivity of coals

Nuclear magnetic resonance (NMR) transverse relaxation time (T2) measurements of fully water-saturated rock samples can provide a reference for pore size distribution (PSD). Commonly, surface relaxivity of the rock must be known before obtaining an absolute PSD sample using NMR data. There are many reports concerning the surface relaxivity of sandstones, shales, and carbonate rocks, however, little research has been performed on the surface relaxivity of coals, which limit the application of the NMR in PSD evaluation of coals. To obtain a standard surface relaxivity for PSD measurements of coals, we performed NMR, low-temperature N2 adsorption (LTNA), and mercury intrusion porosimetry (MIP) measurements for 15 bituminous and anthracite coals, whose Ro range from 0.52% to 3.07%. The results show that the values of surface relaxivity from LTNA (ρ2-SVR) are inconsistent with those from MIP (ρ2-MIP) for all samples. Moreover, the applications of ρ2-SVR and ρ2-MIP for PSD conversions are valid only for the smaller pores and larger pores, respectively. Evidently, both these two surface relaxivities cannot be used individually to calculate full-scale PSD. To obtain the actual surface relaxivity (ρ2) for full-scale PSD, we rebuilt a full-scale PSD by combining the pores smaller than 25 nm from LTNA and the pores larger than 25 nm from MIP. The results indicate that the calculated ρ2 provides excellent function for PSD transformation for all coal samples. Finally, the references of ρ2 for different coals are provided, i.e., values of 2.1 μm/s for sub-bituminous coal (low-rank coal), 3.0 μm/s for bituminous coal (medium-rank coal) and 1.6 μm/s for anthracite coal (high-rank coal). Using these referential surface relaxivities, a T2 distribution from NMR measurement can be converted to a PSD, which is applicable not only in the laboratory but also in field applications such as well logging.

Impact of Brine/CO2 exposure on the transport and mechanical properties of the Mt Simon sandstone

Abstract When sandstone rocks are exposed to CO2-saturated brine, their transport and mechanical properties can change due to brine/CO2-induced chemical reactions. The present study investigates the change in the flow-through characteristics, porosity, and the mechanical behavior of Mt. Simon Sandstone samples caused by exposure to brine/CO2. The cores, extracted from a depth interval of 2110.4–2111.4 m (6924–6927 ft) in the Mt. Simon formation, were first characterized for their mechanical and transport properties, and then aged in CO2-saturated brine at pressures of 17.24 MPa (2500 psi) and temperature of 50 °C for one to two weeks. Following that, the changes in the transport and mechanical properties of the samples were analyzed using He pycnometry, flow perporometry and triaxial testing. Our experiments show that the porosity of the Mt. Simon samples slightly increases after exposure to CO2/brine, while the permeability increases more substantially depending on the stress state. Measurements of the flow-through pore size distribution (PSD) are indicative of the changes occurring and are consistent with the observed increases in permeability. Nitrogen adsorption tests (BET), before and after incubation, show a significant loss of pore volume in the mesoporous range that is indicative of clay dissolution. Weakening of the materials was observed based on the mechanical properties studied, a result that is consistent with the observed dissolution of clays that play a central role in the cementation of the quartz grains. Finally, the analysis of the brine compositions reveals an increase in concentration of most cations after incubation with the Mt. Simon cores. This is also consistent with mineral/clay dissolution, confirmed by the porosity, transport, and mechanical property measurements as well as electron microscopy analysis of the same samples.

Breakthrough pressure and permeability in partially water-saturated shales using methane–carbon dioxide gas mixtures: An experimental study of Carboniferous shales from the eastern Qaidam Basin, China

As an important unconventional and alternative resource, shale gas has attracted worldwide attention. The breakthrough pressure is a major factor in the generation and migration of shale gas as well as in the evaluation of the caprock sealing capacity. Carboniferous shales are considered to have great potential for the exploitation of shale gas; thus, investigations of the breakthrough pressure and gas effective permeability are significant. Two shale samples taken from the Carboniferous Hurleg Formation in the eastern Qaidam Basin, China, were chosen to conduct breakthrough experiments to investigate the effects of water saturation and CO2–CH4 mixed mole fractions on the breakthrough pressure and gas effective permeability. Prior to the experiments, various relevant parameters (e.g., the porosity, mineral composition, and organic geochemistry; the total organic content, thermal maturity and kerogen type; and microstructure) of these samples were also measured. The results of our breakthrough experiments show that the breakthrough pressure increases with the water saturation and decreases with the CO2 mole fraction in the gas mixture. The situation for the gas effective permeability is just the opposite. Pore-size distribution measurements indicate that there are many nanoscale micropores that can easily be blocked by water molecules. This results in the reduced connectivity of gas pathways; thus, the breakthrough pressure increases and the gas effective permeability decreases with increasing water saturation. The breakthrough pressure decreases with the CO2 mole fraction because the interfacial tension of the CO2–water system is smaller than that of the CH4–water system. The viscosity of the CO2–CH4 mixture was found to increase with the CO2 mole fraction by fitting a series of values under the same temperature and pressure conditions, leading to an increase in the gas effective permeability. Furthermore, CO2 molecules are smaller than CH4 molecules, making it easier for CO2 to move across pathways. After each breakthrough experiment, the CO2 mole fraction in the effluent was less than that in the injected gas, and it increased over time until reaching the initial injected gas composition. This is because the adsorption and solubility of CO2 in water are greater than those of CH4. This study provides practical information for further investigations of shale gas migration and extraction and the sealing capacities of caprocks.

Correlation of pore size distribution with thermal conductivity of precipitated silica and experimental determination of the coupling effect

Vacuum insulation panels are high-performance insulating materials with considerably better thermal properties than conventional thermal insulation. Unfortunately, their use is limited to applications where their high price does not matter. To extend the application range of vacuum insulation, the authors try to replace the high-priced core material fumed silica with the cheaper precipitated silica. For this purpose, five commercially available precipitated silica samples were tested for their suitability as core material for vacuum insulations. They were pre-pressed with 5 bar and 30 bar each. To compare their thermal performances, a guarded hot plate apparatus for measuring thermal conductivities under vacuum was developed. The pore size distributions of the samples were measured by mercury intrusion porosimetry and used to calculate the gas thermal conductivity as a function of the residual pressure. For this purpose, a correction factor for the measured pore size distribution is introduced. Additionally, the coupling effect between gaseous and solid thermal conductivity could be determined through comparison with measured data. A model is presented to predict the thermal conductivity curve, even of unknown silica samples, solely using mercury intrusion porosimetry data.

Effects of changes in temperature and heating times in the preparation of mudstones rock samples, on pore size distribution and specific surface BET measurements based on adsorption isotherm analysis

Effects of changes in temperature and heating times in the preparation of mudstones rock samples, on pore size distribution and specific surface BET measurements based on adsorption isotherm analysis

Thermal Conversion of MOF@MOF: Synthesis of an N-Doped Carbon Material with Excellent ORR Performance.

Here we propose a new strategy in which two isomorphic metal-organic frameworks (MOFs) [FJU-40-H (a) and FJU-40-NH2 (b)] are used to construct the core-shell material MOF@MOF. This strategy based on nitrogen doping and specific surface has resulted in an N-doped porous carbon (NPC) material in a one-step thermal treatment in N2 atmosphere; this material displays high catalytic activity for the oxygen reduction reaction (ORR). The materials were analyzed by SEM, XPS, Raman, specific surface area, pore size distribution and electrochemical measurements. It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF. The onset potential is NPC-b@a-4h (-0.068 V)>NPC-a@b-4h (-0.075 V)>NPC-a-4h (-0.109 V)>NPC-b-4h (-0.113 V). Moreover, the results also show that the performance of NPC-b@a (n=4.15) is better than that of NPC-a@b (n=3.32), which means the different nitrogen content of ligands inside and outside of the core affects the ORR properties.

Probe material choice for nuclear magnetic resonance cryoporometry (NMRC) measurements of the nano-scale pore size distribution of unconventional reservoirs

Nuclear magnetic resonance cryoporometry is a newly developed technique that can characterize the pore size distribution of nano-scale porous materials. To date, this technique has scarcely been used for the testing of unconventional oil and gas reservoirs; thus, their micro- and nano-scale pore structures must still be investigated. The selection of the probe material for this technique has a key impact on the quality of the measurement results during the testing of geological samples. In this paper, we present details on the nuclear magnetic resonance cryoporometric procedure. Several types of probe materials were compared during the nuclear testing of standard nano-scale porous materials and unconventional reservoir geological samples from Sichuan Basin, Southwest China. Gas sorption experiments were also carried out on the same samples simultaneously. The KGT values of the probe materials octamethylcyclotetrasiloxane and calcium chloride hexahydrate were calibrated using standard nano-scale porous materials to reveal respective values of 149.3 Knm and 184 Knm. Water did not successfully wet the pore surfaces of the standard controlled pore glass samples; moreover, water damaged the pore structures of the geological samples, which was confirmed during two freeze-melting tests. The complex phase transition during the melting of cyclohexane introduced a nuclear magnetic resonance signal in addition to that from liquid in the pores, which led to an imprecise characterization of the pore size distribution. Octamethylcyclotetrasiloxane and calcium chloride hexahydrate have been rarely employed as nuclear magnetic resonance cryoporometric probe materials for the testing of an unconventional reservoir. Both of these materials were able to characterize pore sizes up to 1 μm, and they were more applicable than either water or cyclohexane.

KG²B, a collaborative benchmarking exercise for estimating the permeability of the Grimsel granodiorite—Part 2: modelling, microstructures and complementary data

Measuring and modelling the permeability of tight rocks remains a challenging task. In addition to the traditional sources of errors that affect more permeable formations (e.g. sample selection, non-representative specimens, disturbance introduced during sample acquisition and preparation), tight rocks can be particularly prone to solid–fluid interactions and thus more sensitive to the methods, procedures and techniques used to measure permeability. To address this problem, it is desirable to collect, for a single material, measurements obtained by different methods and pore fluids. For that purpose, a benchmarking exercise involving 24 laboratories was organized for measuring and modelling the permeability of a single low-permeability material, the Grimsel granodiorite. The objectives of the benchmark were: (i) to compare the results for a given method, (ii) to compare the results between different methods, (iii) to analyse the accuracy of each method, (iv) to study the influence of experimental conditions (especially the nature of pore fluid), (v) to discuss the relevance of indirect methods and models and finally (vi) to suggest good practice for low-permeability measurements. To complement the data set of permeability measurements presented in a companion paper, we focus here on (i) quantitative analysis of microstructures and pore size distribution, (ii) permeability modelling and (iii) complementary measurements of permeability anisotropy and poroelastic parameters. Broad ion beam—scanning electron microscopy, micro-computerized tomography, mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) methods were used to characterize the microstructures and provided the input parameters for permeability modelling. Several models were used: (i) basic statistical models, (ii) 3-D pore network and effective medium models, (iii) percolation model using MICP data and (iv) free-fluid model using NMR data. The models were generally successful in predicting the actual range of measured permeability. Statistical models overestimate the permeability because they do not adequately account for the heterogeneity of the crack network. Pore network and effective medium models provide additional constraints on crack parameters such as aspect ratio, aperture, density and connectivity. MICP and advanced microscopy techniques are very useful tools providing important input data for permeability estimation. Permeability measured—orthogonal to foliation is lower that—parallel to foliation. Combining the experimental and modelling results provide a unique and rich data set.

Influence of tarry material deposition on low-strength cokes or pyrolyzed chars of low rank coals on the strength

In this fundamental laboratory scale investigation, carbon/carbon (C/C) composites were prepared from a mixture of pyrolyzed-chars of low-rank coals (lignite and sub-bituminous coals) or low-strength cokes (drum index: DI1506 = 52 and 73) and coke-oven gas (COG) tar to investigate the possibility of producing high-strength coke for blast furnace use from low-grade coals or cokes. In addition, the optimum conditions for composite preparation and the influence of the tarry material on the strength of the prepared C/C composite was examined. The C/C composites were prepared as follows: the tar was first added over particles of coke or char at room temperature, subsequently, the mixture was pyrolyzed at a predetermined temperature (500–900 °C) in an inert atmosphere. The indirect tensile strength of the C/C composite prepared at a pyrolysis temperature of 500 °C increased with increasing weight ratio of tar to cokes (3.5–4.5 MPa) or chars (2.0–3.0 MPa) up to a ratio of 2.0; at this point, the indirect tensile strength reached approximately 6.0 MPa. The indirect tensile strength of the C/C composites prepared with the weight ratio of tar to cokes/chars of 2.0 also increased with increasing pyrolysis temperature, reaching approximately 7.0–7.5 MPa at 800–900 °C, which was comparable to the ca. 7.0 MPa strength of the high-grade cokes (DI1506 = 87) used in commercial blast furnaces. Based on pore size distribution measurements using the mercury intrusion porosimetry, N2 adsorption, and polarized optical microscope methods, it was likely that the increase in the indirect tensile strength of the prepared C/C composite occurred because of the vapor infiltration of tar-derived carbonaceous materials into the micro-, meso- and macro-pores in the low-grade cokes and pyrolyzed chars during the pyrolysis of the mixtures.

A pore structure based real gas transport model to determine gas permeability in nanoporous shale

Gas flows in the forms of multiple transport mechanisms in shale nanoporous media with complex pore structure and different pore types. Laboratory pressure pulse decay technique is often applied to measure gas permeability but the current gas permeability interpretation model is mostly based on the homogeneous macro scale model while the influence of pore structure on real gas transport is neglected. In this study, a novel pore structure based real gas transport model is proposed to determine gas permeability in nanoporous shale combining laboratory pressure pulse decay technique with pore network simulation. The laboratory pressure pulse decay process is simulated in a virtual system based on the similarity principle which contains upstream vessel, downstream vessel, and core sample. The core sample is constructed by a series of connected pore networks and the sizes of pores and throats in each location of the pore network are randomly assigned according to laboratory measured pore size distribution. Gas transport mechanisms inside the core sample consider viscous flow, Knudsen diffusion, surface diffusion and real gas effect. At each time step, the upstream vessel pressure decreases and the downstream vessel pressure increases until the upstream vessel pressure and downstream vessel pressure become equal. The simulated pressure drop versus time curve is obtained and is applied to fit the laboratory measured pressure drop data by repeating core sample construction and pressure pulse decay process. The proposed model is applied to measure gas permeability of Sichuan basin, Longmaxi formation shale core sample. The results indicate that the predicted value based on the proposed model matches well with the experimental measured pressure drop data. The proposed model is used to study the influences of test gas type and pore size on gas permeability. When the average organic pore radius is less than 20 nm, helium tested permeability overestimates at least 40% of the methane permeability.

A comparative anion diffusion study on different argillaceous, low permeability sedimentary rocks with various pore waters

Through-diffusion experiments with tritiated water (HTO) and 36Cl− as a function of pore water concentration (0.01–5 M) were performed on two Ordovician-age argillaceous rock samples from the Blue Mountain Fm and Queenston Fm shales of the Paleozoic intracratonic Michigan Basin in Canada. This study reveals that the effect of ionic strength on the anion-transport porosity is similar, and only the minimal anion excluded porosity is higher in the Blue Mountain Fm shale. The differences in rock sample mineralogy cannot explain this effect. It is hypothesized that the structure of the Blue Mountain Fm shale samples has led to pore space openings sufficiently small that they behave as interlayers. Such pores are defined as interlayer equivalent (ILE) pores. These ILE pores, as in the case of interlayer pores, can act to permanently limit the anion-accessible porosity. Pore-size distribution measurements provide further evidence of increased potential for ILE pores within the Blue Mountain Fm samples. A Donnan model, which includes consideration of both ILE and uncharged pores, is shown to describe the effect of molar concentration on the anion-accessible porosity in the argillaceous rocks investigated.

Measuring and predicting pore size distribution of freeze-dried solutions

ABSTRACTIn this work, a novel procedure is presented for the measurement and prediction of pore size distribution of freeze-dried solutions in vials. A method based on segmentation is proposed for determining the size of the pores left by ice crystals, using images obtained by scanning electron microscopy. The original ice crystal size distribution is also predicted using a mathematical model based on balance equations. The model predictions and the results of the segmentation technique show a fairly good agreement. The proposed procedure could be used to efficiently estimate the resistance to mass transfer during drying and hence optimize the freeze-drying process.

Mono- and bimetallic nanoparticles decorated KTaO3 photocatalysts with improved Vis and UV–Vis light activity

Novel mono- and bimetallic nanoparticles (MNPs and BNPs) decorated surface of perovskite-type KTaO3 photocatalysts were successfully synthesized by hydrothermal reaction of KTaO3 followed by photodeposition of MNPs/BNPs. The effect of noble metal type (MNPs = Au, Ag, Pt, Pd, Rh, Ru or BNPs = Au/Pt, Ag/Pd, Rh/Ru), amount of metal precursor (0.5, 1.0, 1.5 or 2.0 wt%) as well as photoreduction method (simultaneous (both) or subsequent (seq) deposition of two metals) on the physicochemical and photocatalytic properties of MNPs- and BNPs-KTaO3 have been investigated. All as-prepared photocatalysts were subsequently characterized by UV–Vis diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET) specific surface area and pore size distribution measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectroscopy. The crystal structure was performed using visualization for electronic and structural analysis (VESTA). The photocatalytic activity under Vis light irradiation was estimated in phenol degradation in aqueous phase and toluene removal in gas phase, while under UV–Vis light irradiation was measured amount of H2 generation from formic acid solution. The absorption properties of O2 and H2O molecules on KTaO3(1 0 0) surface supported by Au or Au/Pt NPs was also investigated using density-functional theory (DFT). The experimental results show that, both MNPs-KTaO3 and BNPs-KTaO3 exhibit greatly enhanced pollutant decomposition efficiency under Vis light irradiation and highly improved H2 production under UV–Vis light irradiation compared with pristine KTaO3. MNPs deposition on KTaO3 surface effects by disperse metal particle size ranging from 11 nm (Ru NPs) to 112 nm (Au NPs). Simultaneous addition of Au/Pt precursors results in formation of agglomerated larger metal nanoparticles (50–100 nm) on KTaO3 surface than subsequent deposition of Au/Pt with composition of concentrated smaller metal nanoparticles (>50 nm) on KTaO3 surface. The 0.5 Au/1.5 Pt-KTaO3_both and 2.0 Rh-KTaO3 reveal the highest Vis-induced activity among prepared samples in aqueous phase (14.75% of phenol decomposition after 90 min of irradiation) and gas phase (41.98% of toluene removal after 60 min of irradiation), respectively. The theoretical calculations confirmed that adsorption energy of O2 and H2O molecules was increased after loading of Au or Au/Pt NPs on KTaO3(1 0 0) surface. Control tests with scavengers show that O2− radical is significantly involved in phenol oxidation under Vis light irradiation, which proposed mechanism is based on direct electron transfer from MNPs/BNPs to conduction band of KTaO3. The highest amount of H2 evaluation is obtained also by 0.5 Au/1.5 Pt-KTaO3_both after 240 min of UV–Vis light irradiation (76.53 µmol/min), which is eleven times higher than for pristine KTaO3 (6.69 µmol/min). Moreover, the most photocatalytic samples for each model reaction present good repeatability and stability after subsequent three cycles. Summarized, MNPs- and BNPs-KTaO3 are promising material in advanced applications of photocatalysis.

Accounting for Water Stored in Superabsorbent Polymers in Increasing the Degree of Hydration and Reducing the Shrinkage of Internally Cured Cementitious Mixtures

Abstract The use of superabsorbent polymers (SAPs) in cementitious materials has attracted much attention recently due to the potential benefits associated with internal curing. In this study, a commercially produced SAP is characterized using pore solution absorption and desorption measurements. The SAP helps maintain higher internal relative humidity in the pastes, resulting in a reduction in autogenous shrinkage. This paper explores the effects of partial SAP replacements and compares the results to those obtained using a previously developed relationship based on pore size distribution and relative humidity measurements, which aims to predict the reduction in shrinkage coming from additional internal curing water. Using this approach reduces the amount of SAP used for internal curing, as compared to the more conventional design methodology, which is based on providing a volume of internal curing water that is equivalent to the total chemical shrinkage. Experimental data showed that only a fraction of the provided internal curing water ends up filling the pores and reducing the autogenous shrinkage. Other factors, such as increased degree of hydration and partial desorption of the internal curing agent, account for the sharing of the available internal curing water. The aforementioned approach was modified to consider these factors. It can be concluded that using lower amounts of SAP results in substantial reduction of autogenous shrinkage at early ages, and the developed relationship predicts this shrinkage reduction.

Intelligent methods for predicting nuclear magnetic resonance of porosity and permeability by conventional well-logs: a case study of Saharan field

In the well-log data processing, the principal advantage of the nuclear magnetic resonance (NMR) method is the measurement of fluid volume and pore size distribution without resorting to parameters such as rock resistivity. Preliminary processing of the well-log data allowed first to have the petrophysical parameters and then to evaluate the performances of the transverse relaxation time T 2 NMR. Petrophysical parameters such as the porosity of the formation as well as the effective permeability can be estimated without having recourse the fluid type. The well-log data of five wells were completed during the construction of intelligent models in the Saharan oil field Oued Mya Basin in order to assess the reliability of the developed models. Data processing of NMR combined with conventional well data was performed by artificial intelligence. First, the support vector regression method was applied to a sandy clay reservoir with a model based on the prediction of porosity and permeability. NMR parameters estimated using intelligent systems, i.e., fuzzy logic (FL) model, back propagation neural network (BP-NN), and support vector machine, with conventional well-log data are combined with those of NMR, resulting in a good estimation of porosity and permeability. The results obtained during the processing are then compared to the FL and NN regression models performed by the regression method during the validation stage. They show that the correlation coefficients R 2 estimated vary between 0.959 and 0.964, corresponding to the root mean square error values of 0.20 and 0.15.

Analysis of Water Forms in Lignite and Pore Size Distribution Measurement Utilizing Bound Water as a Molecular Probe

Based on the congelation characteristics, different types of water in lignite and their drying behavior were investigated by using low-temperature differential scanning calorimetry over a temperature range from 25 to −80 °C. The water in lignite was classified into three types: free water, bound water, and nonfreezable water. It was shown that during drying, the free water in lignite was removed first, and then the bound water began to be evaporated. With the moisture decreasing, the congelation peak of free water moves toward lower temperature, which may be explained by the formed capillary force distribution in the pores driving the free water to flow toward the smaller pores and increasing the confinement effect of the pores. However, for bound water, this mobility was restricted by the stronger coal–water interaction; thus, its congelation peak remained at around −42 °C. The amounts of three types of water were determined by a new method. It shown that all of the bound water and more than 30% of nonfr...

Characterization of micro-nano pore networks in shale oil reservoirs of Paleogene Shahejie Formation in Dongying Sag of Bohai Bay Basin, East China

Abstract For typical blocky, laminated and bedded mudrock samples from the Paleogene Shahejie Formation in the Dongying Sag of Bohai Bay Basin, this work systematically focuses on their structure characterization of multiple micro-nano pore networks. A use of mercury injection capillary pressure (MICP) documented the presence of multiple μm-nm pore networks, and obtained their respective porosity, permeability and tortuosity. Different sample sizes (500-841 μm GRI fractions, 1 cm-sized cubes, and 2.54 cm in diameter and 2-3 cm in height core plugs) and approaches (low-pressure N 2 gas physisorption, GRI matrix permeability, MICP, helium pycnometry, and pulse decay permeameter) were used to measure pore size distribution, porosity and permeability. The average porosity and matrix permeability determined from MICP are (6.31±1.64)% and (27.4±31.1)×10 -9 μm 2 , the pore throat diameter of pores is mainly around 5 nm, and the median pore throat diameter based on 50% of final cumulative volume is (8.20±3.01) nm in shale. The pore-throat ratios decrease with a decrease of pore size diameter. Moreover, the permeability of shale samples with lamination is nearly 20 times larger than matrix permeability. The geometrical tortuosity of the nano-scale 2.8−10.0 nm pore networks is 8.44 in these shales, which indicates a poor connectivity of matrix pore network and low flow capability. Overall, the variable and limited pore connectivity of shale samples will affect hydrocarbon preservation and recovery.

Applying octamethylcyclotetrasiloxane as a probe liquid for characterizing the pore size distribution of oil-bearing tight sandstones by nuclear magnetic resonance cryoporometry

The characterization of tight sandstone pore structure is extremely important to the study of tight sandstone oil and gas. There are many techniques for the quantitative analysis of pore size distribution (PSD) in tight sandstone. Nuclear magnetic resonance cryoporometry (NMRC) is a relative new method that can be applied to obtain PSD of porous materials. However, the choice of the NMRC probe liquid is critical to the test result. In this study, we used a potential probe liquid named octamethylcyclotetrasiloxane (OMCTS) for NMRC. OMCTS, exhibiting excellent properties, such as amphiphilic wetting, a large KGT, and superior NMR behavior, has obvious advantages over water as a probe liquid for the PSD measurement of tight sandstone by NMRC, especially for oil-bearing tight sandstone. The applicability of this probe liquid for measuring nanometer pores is demonstrated through the accurate measurement of standard sample. The PSDs of four tight sandstone samples with different wettability from the Upper Triassic Yanchang Formation in Ordos Basin are measured by OMCTS. Mercury intrusion capillary pressure (MICP) is also performed on all samples for comparison. The experimental results show that OMCTS can measure pores in tight sandstone from 4 to 1400 nm. OMCTS can, as NMRC probe liquid, not only measure the PSD of hydrophilic tight sandstone, but also oil-wet tight sandstone. Furthermore, OMCTS does not damage the pore structure of tight sandstone. We think the NMRC with OMCTS as probe liquid will be proved to be a useful complement to current methods.