Methane Adsorption Capacity Research Articles

Reservoir Characteristics of the Lower Jurassic Lacustrine Shale in the Eastern Sichuan Basin and Its Effect on Gas Properties: An Integrated Approach

The exploration of shale gas in Fuling area achieved great success, but the reservoir characteristics and gas content of the lower Jurassic lacustrine in the northern Fuling areas remain unknown. We conducted organic geochemical analyses, Field Emission Scanning Electron Microscope (FE-SEM), X-ray diffraction (XRD) analysis, high-pressure mercury intrusion (MIP) and CH4adsorption experimental methods, as well as NMR logging, to study mineral composition, geochemical, pore structure characteristics of organic-rich shales and their effects on the methane adsorption capacity. The Da’anzhai shale member is generally a set of relatively thick (avg. 75 m) and high carbonate-content (avg. 56.89%) lacustrine sediments with moderate total organic carbon (TOC) (avg. 1.12%) and thermal maturation (Vitrinite reflectance (VR): avg. 1.19%). Five types of lithofacies can be classified: marl (ML), calcareous shale (CS), argillaceous shale (AS), muddy siltstone (MS), and silty shale (SS). CS has good reservoir quality with a high porosity (avg. 4.72%). The small pores with the transverse relaxation time of 0.6–1 ms and 1–3 ms comprised the major part of the porosity in the most lithofacies from Nuclear magnetic resonance (NMR) data, while the large pore (>300 ms) accounts for a small porosity proportion in the CS. The pores mainly constitute of mesopores (avg. 23.2 nm). The clay minerals with a large number of interparticle pores in the SEM contributes most to surface area in the shale lithofacies with a moderate TOC. The adsorption potential of shale samples is huge with an average adsorption capacity of 4.38 mL/g and also has high gas content (avg. 1.04 m3/t). The adsorption capacity of shale samples increases when TOC increases and temperature decreases. Considered reservoir properties and gas properties, CS with the laminated structures in the medium-upper section of the Da’anzhai member is the most advantage lithofacies for shale gas exploitation.

Effect of Kerogen Thermal Maturity on Methane Adsorption Capacity: A Molecular Modeling Approach.

The presence of kerogen in source rocks gives rise to a plethora of potential gas storage mechanisms. Proper estimation of the gas reserve requires knowledge of the quantities of free and adsorbed gas in rock pores and kerogen. Traditional methods of reserve estimation such as the volumetric and material balance approaches are insufficient because they do not consider both the free and adsorbed gas compartments present in kerogens. Modified versions of these equations are based on adding terms to account for hydrocarbons stored in kerogen. None of the existing models considered the effect of kerogen maturing on methane gas adsorption. In this work, a molecular modeling was employed to explore how thermal maturity impacts gas adsorption in kerogen. Four different macromolecules of kerogen were included to mimic kerogens of different maturity levels; these were folded to more closely resemble the nanoporous kerogen structures of source rocks. These structures form the basis of the modeling necessary to assess the adsorption capacity as a function of the structure. The number of double bonds plus the number and type of heteroatoms (O, S, and N) were found to influence the final configuration of the kerogen structures, and hence their capacity to host methane molecules. The degree of aromaticity increased with the maturity level within the same kerogen type. The fraction of aromaticity gives rise to the polarity. We present an empirical mathematical relationship that makes possible the estimation of the adsorption capacity of kerogen based on the degree of polarity. Variations in kerogen adsorption capacity have significant implications on the reservoir scale. The general trend obtained from the molecular modeling was found to be consistent with experimental measurements done on actual kerogen samples. Shale samples with different kerogen content and with different maturity showed that shales with immature kerogen have small methane adsorption capacity compared to shales with mature kerogen. In this study, it is shown for the first time that the key factor to control natural gas adsorption is the kerogen maturity not the kerogen content.

Adsorption of silver nano-particles modified activated carbon filter media for indoor formaldehyde removal

To improve the efficiency of formaldehyde removal using activated carbon, surface modification is required. One promising example of such a surface treatment is the coating on the activated carbon surface with silver and silver oxide. By increasing the specific surface area of activated carbon and surface oxygen functional groups, the activated carbon is chemically enhanced for formaldehyde removal. It was confirmed that adsorption capacity of formaldehyde treated with 0.001M AgNO3-AC at different formaldehyde concentrations are higher than that of unmodified activated carbon. It also has a longer adsorption time at different formaldehyde concentrations.

Quantitative Analysis of Pore Structure and Its Impact on Methane Adsorption Capacity of Coal

Better understanding of the storage and transportation characteristics of methane in coal seams is important to further develop and utilize the methane resources in the coalbed. This study is devoted to investigating the relationship between methane adsorption performance and pore structure by analyzing twelve coal samples derived from the typical methane-rich coalbeds in China. To eliminate the influence of inorganic components such as ash in different coal samples, a specific fixed-bed reactor with internals was employed for the coal treatment. Based on N2/CO2 adsorption analysis at low-pressure condition, the pores in coal were classified into three types in this study: ultra-micropore (pore width ultra-micropore surface area (0.8976) > fractal dimension D1 (0.8862) > N2-BET surface area (0.7915) > micropore volume (0.5035) > micropore surface area (0.5006). This study shows the influence of parameters of pore structure on methane adsorption of coal and clarifies the order importance of these parameters by the GRA method.

Full-scale nanopore system and fractal characteristics of clay-rich lacustrine shale combining FE-SEM, nano-CT, gas adsorption and mercury intrusion porosimetry

Shale pore structures and irregularities are significant for gas adsorption and interstifial flow. High complexity and nonuniformity, wide pore scales, and multiple morphology hinder the thorough characterization of multi-scale pore structure and heterogeneity in shales. In this work, the geochemistry, pore structure and fractal characteristics of the Upper Cretaceous Nenjiang shale in the Songliao Basin of NE China were investigated, combining geochemistry experiments, physical property analysis, FE-SEM and nano-CT image observation, CO2/N2 gas adsorption, mercury intrusion porosimetry, and methane methane sorption analysis. The results show that the Nenjiang shales are low-mature (Ro of 0.55%–0.93%) and rich in organic matters (OMs) and clays. The size diameters of shale pores are generally distributed in sizes of 0.3–0.8, 1.4–4.5, 80–600 nm and 10–80 μm. Shale pores have strong heterogeneity and complexity, good connectivity and openness, mainly with inkbottle- and slit-shapes. Total pore volume (PV) is positive correlate with specific surface area (SSA), porosity and permeability, but negative correlate with the average pore size. The development of micro-, meso-, and macro-pores were dominated by the contents of OM, clays, and quartz, respectively. Positive correlations were found among fractal dimension, contents of OMs and clays, total PV, SSA, and methane adsorption capacity, which would provides better understanding on reservoir assessment and shale gas storage capacity.

Well-defined meso/macroporous materials as a host structure for methane hydrate formation: Organic versus carbon xerogels

A series of xerogels with a properly designed porous structure and surface chemistry have been synthesized and evaluated as a host structure to promote the nucleation and growth of methane hydrates. Organic xerogels (OGs) have been synthesized from resorcinol-formaldehyde mixtures using a sol-gel approach and microwave heating. These xerogels are hydrophilic in nature and possess designed meso/macrocavities in the pore size range 5–55 nm. Carbon xerogels (CGs) have been synthesized from their organic counterparts after a carbonization treatment at high temperature. Interestingly, the carbonization process does not alter/modify substantially the porous network of the parent xerogels, while developing new micropores. Under water-supplying conditions, the two types of xerogels exhibit a large improvement in the methane adsorption capacity compared to the pure physisorption process taking place in dry conditions (up to 200% improvement), and associated with a significant hysteresis loop. These excellent values must be associated with the promoting effect of these xerogels in the water-to-hydrate conversion process. The comparison of OGs and CGs as a host structure anticipates that surface chemistry, total pore volume and pore size are critical parameters defining the extent and yield of the methane hydrate formation process.

Pore structure characteristics and hydrocarbon generation potential of middle Jurassic lacustrine source rocks in the Yuka depression, Qaidam Basin, NW China: Implications from petrographic and organic geochemical analyses

The Yuka depression is one of the most important energy production bases in the Qaindam Basin. Although shales in the 7th member of the Dameigou Formation (J2d7) are key members of Middle Jurassic Petroleum System, organic geochemistry and petrography of different rock facies have not been fully analyzed. In this study we evaluate hydrocarbon generation potential of the J2d7 by applying integrated petrographic, geochemical and mineralogical analyses. In addition, pore structure is characterized using field emission scanning electron microscopy (SEM), CO2 and N2 physisorption. Results indicate that mudstone, carbonaceous-mudstone and siltstone have total organic carbon (TOC) values of 2.64%, 5.61% and 0.48%, respectively, as well as variations in the hydrogen index (HI). Kerogen types are mainly Type Ⅲ, with maturity varying from marginally mature to mature. Notably, excess methane adsorption capacities were higher in the carbonaceous-mudstone sample (4.66 cm3/g) than in the mudstone sample (1.78 cm3/g). Primary minerals in the mudstone were quartz and clay; kaolinite, illite and illite/smectite (I/S) were the dominant clay minerals. Clay minerals and TOC content, as well as positive correlations between illite, I/S and mesopore SSA, were factors controlling pore structure development; in contrast, kaolinite contents were negatively correlated with SSA. Liptinite is the dominant maceral composition and a high content of C29 regular sterane in the carbonaceous-mudstones suggests primary higher-plant input, associated with a low gammacerane index (0.28–0.32) and a high pristane/phytane (Pr/Ph) ratio (3.02–3.96). Petrographic and geochemical results indicate an alternating depositional environment across suboxic semi-saline to oxic fresh water changes. Higher-plants were predominant and a small quantity of algae were preserved through in-situ accumulation and migration during shale development; an oxic water column with carbonaceous-mudstone was also present. Although organic matter was marginally mature to mature, the abundance of liptinite (average of 63%) was derived from higher-plants, possibly being the primary materials producing gaseous hydrocarbons.

Methane separation from diluted mixtures by fixed bed adsorption using MOFs: Model validation and parametric studies

Adsorption of methane from diluted methane/nitrogen mixtures in a fixed bed reactor was experimentally studied and modelled in this work. Three different Metal-Organic Frameworks (MOFs), Basolite C300, F300 and A100 were considered for this purpose, the adsorption bed being operated at 298 K, 0.1 MPa, and an inlet methane concentration of 2%. Methane adsorption capacities decrease in the order: Basolite C300 (0.078 mmol/g) > Basolite F300 (0.040 mmol/g) > Basolite A100 (0.028 mmol/g). In addition, a mechanistic model based on the numerical solution of an heterogeneous one-dimensional model considering axial dispersion has been used for modelling these adsorption results.Proposed model provides a reasonable fitting of the experimental fixed bed results (R2 > 0.9), using internal diffusion and axial dispersion as fitting parameters. Variation of these parameters can be explained in terms of adsorbent morphological features. Proposed model has been successfully extended to other methane adsorption processes reported in the literature, as well as to thermal desorption of methane from MOF-containing fixed bed reactors. The experimentally validated model has been used to predict the effect of main operation parameters on the performance of the MOF-based fixed beds for methane adsorption.

Methane adsorption characteristics of overmature Lower Cambrian shales of deepwater shelf facies in Southwest China

The Lower Cambrian shales of deepwater shelf facies comprise an important part of the marine black shales in southern China. In this study, twenty-four Lower Cambrian shale samples from southwest China were subjected to analysis of geochemistry, pore structure and methane adsorption capacity. The samples have total organic carbon (TOC) contents ranging from 0.25% to 11.3% and equivalent vitrinite reflectance (EqVRo) values in the range of 2.51–4.23%. Specific surface areas determined from N2 adsorption at 77.4 K and specific micropore volumes from CO2 adsorption at 273.15 K are in the range of 3.0–38.6 m2/g rock and 2.5–11.4 cm3/kg rock, respectively, and both of them have positive relationships with TOC values. The Langmuir volumes of these samples at 60 °C range from 0.47 cm3/g rock to 5.96 cm3/g rock and are positively correlated with TOC values, which on the one hand confirms the TOC control on methane adsorption capacity and on the other hand also suggests a weak control of thermal maturity on methane adsorption capacity at overmature stages. Although both specific surface area and specific micropore volume are positively correlated with methane adsorption capacity, the latter seems to have a stronger effect and the specific micropore volume determined from subcritical CO2 adsorption may be considered as a proxy for the volume of adsorbed methane in dry shales. For the extrapolation of measured methane excess adsorption isotherms to geological conditions, the use of a constant or varying Langmuir volume makes no significant difference with respect to the methane storage capacity of shales when the density of the adsorbed methane is allowed to change with temperature. However, the absolute methane adsorption quantity at subsurface is obviously dependent on the use of a constant or varying Langmuir volume, which subsequently affects the estimation of the relative percentages of adsorbed and free methane.

Competitive adsorption characteristics of N2 and CH4 gas mixtures on coal and its geological significance

Coalbed methane (CBM) is an important unconventional natural gas resource and has achieved great advances in recent years. In this study, single and binary component adsorption experiments of N2 and CH4 on dry coal from eastern Yunnan and western Guizhou area were conducted on a high-pressure isothermal adsorption equipment to investigate the competitive adsorption characteristics of N2 and CH4. The results show that absolute adsorption capacity of methane is higher than that of nitrogen for coal samples in this area. Moreover, maximum mixture gas adsorption isotherms lie between the pure N2 isotherms and pure CH4 isotherms. There is an obvious increasing trend for PL as the content of nitrogen increases, it can be ruled out that critical desorption pressure increases along with the increasing nitrogen content in coal seam. This investigation is significative to understand CBM recovery processes considering N2 injection.

Coal characterization and coalbed methane potential of the Chico-Lomã Coalfield, Paraná Basin, Brazil – Results from exploration borehole CBM001-CL-RS

The aim of this study was to determine the coal characteristics in the Chico-Lomã coalfield, Brazil and to evaluate the potential of natural gas associated with the coal seams (CBM), by carrying out a test well (CBM001-CL-RS) for collecting coal samples, followed by gas desorption measurements, and petrographical and chemical analyses of the coals and their methane adsorption capacities. The gas collected was analyzed for gas composition, stable carbon and hydrogen isotopes. The results indicate a cumulative coal thickness of 11.46 m in well CBM001-CL-RS, associated with an igneous intrusion of 10 m thickness. In the contact zone with the intrusion, the organic matter is severely altered with partial transformation of the coal to natural coke at distances less than 2 m from the intrusion. The ash content, based on proximate analysis, shows a variation from 29.1 to 82.8 wt.%. The sulphur content ranges from 0.43 to 3.89 wt.% and shows higher values in samples from the top of the Rio Bonito Formation. The gas desorption measurements range from 0.05 to 0.74 cm3/g, with methane being the predominant gas (>90%). A thermal origin of the gas is suggested by C and H isotopes and the C1 (methane) to C3 (propane) hydrocarbon distribution. The methane adsorption capacity of the samples varies from 2.50 to 6.50 cm3/g. Changes in microporosity related to thermal alteration may have a significant impact on the gas-holding capacity of samples located near the contact to the intrusion. For the study area, a 3D geological model was generated to estimate the volume of coal in the coalfield, followed by assessment of the gas volume associated with the coal. Based on the 3D model, a preliminary appraisal indicates resources of 7.2 billion tons of coal for the Chico-Lomã coalfield, associated with 2.7 billion m3of gas.

Formaldehyde adsorption capacity of chitosan derivatives as bio-adsorbents for wood-based panels

Chitosan and its derivatives (grafted chitosan and chitosan nanoparticles) were used as bio-based adsorbents in urea-formaldehyde (UF) resins, and accordingly, their effects on the curing behavior, resin structure, crystalline structure, and formaldehyde emission (FE) of final resin has been investigated. Synthesis of grafted chitosan and chitosan nanoparticles was confirmed by FTIR spectroscopy. Characteristics of UF resins were monitored by 13C NMR and X-ray diffraction. This analysis showed that the free formaldehyde and crystallinity of UF resin having chitosan-based adsorbents were substantially reduced. The FE was largely decreased in the medium density fiberboard (MDF) containing chitosan nanoparticles (60%), followed by grafted chitosan (34%) and chitosan powder (22%). A FE class of F**** (<0.3 mg/mL) was obtained by addition of only 1% chitosan nanoparticles (0.21 mg/L). Unexpectedly, increasing the amount of chitosan nanoparticles conversely raised the formaldehyde emission from MDF. The mechanical and physical properties of panels were not significantly changed with the addition of chitosan-based adsorbents.

Effect of supercritical CO2 saturation pressures and temperatures on the methane adsorption behaviours of Longmaxi shale

Abstract To investigate the effects of supercritical CO2 (SC–CO2) saturation pressures and temperatures on the methane adsorption capacity of shale, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscope and energy dispersive spectrometer (SEM/EDS) analysis, low-pressure N2 adsorption (LP-NA), and high-pressure methane adsorption (HP-MA) were conducted on raw and SC–CO2–saturated (8, 12, 16 MPa; 40, 60, 80 °C) shale collected from the Sichuan Basin. Results indicate that the excess adsorption isotherm of shale to methane clearly exhibited excess adsorption characteristics with increasing adsorption pressures. This excess methane adsorption capacity decreased after SC-CO2 saturation and is mainly attributable to decreases in the TOC content, clay minerals and specific surface area (SSA) in the SC–CO2–saturated shale. The density of adsorbed phase methane was considered at different adsorption models, and the results suggest that the Langmuir-Freundlich (LF) and Dubinin-Astakhov (DA) models better describe methane adsorption behaviours than the Langmuir and Ono-kondo models. The methane adsorption capacity of shale is closely related to the solubility of SC-CO2, which decreased significantly with increasing SC-CO2 saturation time and pressure, while the influence of SC-CO2 saturation temperatures was not evident at low-pressure (8 MPa). This study provides a theoretical reference for CO2 enhanced shale gas recovery.

Investigation of enhancing multi-gas transport ability of coalbed methane reservoir by oxidation treatment

Subbituminous coal (Coal S) and anthracite coal (Coal A) were taken as the coal samples and H2O2, NaClO and ClO2 as the oxidants to investigate multi-gas transport ability enhancement of coalbed methane reservoir after oxidation. Thin section, dissolution rate and organic carbon content were measured to analyze the mechanism for different coal ranks and various oxidants. The dissolution rate of Coal A was greater than Coal S because large amounts of ferrous ions in Coal A had strong catalytic effect on Fenton reaction. However, there was large amounts of siderite composed of ferric ions in Coal S, which did not catalyze Fenton reaction. Meanwhile, the adsorption/ desorption behavior of both raw and treated coal samples was measured. Results show that, besides reaction between oxidants and organic matter/ pyrite/ clay minerals could destroy methane adsorption point in coals, weakening methane adsorption capacity. Also, the gas transport channels were widened and interconnected due to the oxidation dissolution and significant temperature increment during oxidation reaction. It is indicated that the reaction between coals and oxidants accelerated methane desorption, widened the methane mass transfer channel, and finally enhanced the methane multi-gas transport ability of methane in coal. The order of multi-gas transport ability enhancement by oxidation treatment under the condition of similar redox potential of oxidants was Coal ASFW > Coal AClO2 > Coal ANaClO > Coal AH2O2 and that of Coal S was Coal SSFW > Coal SH2O2 > Coal SNaClO > Coal SClO2.

An adsorption model for evaluating methane adsorption capacity in shale under various pressures and moisture

Shale generally contains water that has a significant effect on the adsorption of methane in shale. Since methane in shale is mostly stored in an adsorbed state, understanding the effect of moisture on shale adsorption behavior will play a vital role in shale gas development. In this paper, an adsorption model has been proposed to consider the effects of moisture to describe the methane adsorption behavior in wet shale. The model modified the actual methane gas pressure in reservoirs, which to evaluate accurately the methane adsorption levels in the reservoir. Moreover, the model also quantitatively described the degree of influence that moisture in shale had on the amount of shale methane adsorbed. Published data have been used to further verify the applicability of the model. Results have shown that, during a change in gas pressure, the methane adsorption amount in shale revealed a typical “three-stage” change law. With an increase in moisture, the methane adsorption level decreased linearly owing to the inhibitory effect of water molecules on methane adsorption. In terms of test data matching, the calculated results of the model were in approximate agreement with the measured values, indicating that the model could better describe the adsorption behavior in aquifers. Additionally, the classic Langmuir model, the Langmuir-Freundlich model, and the D-A model have been used as comparison with the proposed model in this paper. The comparison results showed that the model proposed in this paper could better quantify the effects of moisture on methane adsorption. And it possessed advantages over models, such as the Langmuir one, under high pressure conditions. In addition, because of the hydrophilic nature of shale, methane could only be adsorbed at a lower energy adsorption site, which indicated that the adsorption heat on wet shale was significantly lower than that in dry shale.

Characteristics of low-rank coal reservoir and exploration potential in Junggar Basin: new frontier of low-rank CBM exploration in China

Low-rank coal reservoirs of Badaowan Formation and Xishanyao Formation are mainly developed in Junggar Basin. This paper discussed their features and coalbed methane (CBM) exploration potential based on geological survey, coal samples testing and mathematical fitting analysis. The pores are mainly small-micro- and large pores, and the porosity is 3.25–27.4% with an average of 9–10.51%; and macro-cracks and micro-fissures are well developed leading to a great variation of the permeability. The shallow coal reservoirs are mostly undersaturated, and the gas saturation tends to increase toward the deep coalbed. The J2x has a stronger methane adsorption and storage capacity than that of J1b and better physical properties, making CMB recovery easier. The coalbed reservoirs in middle-east of southern margin, eastern part and hinterland of Junggar Basin reach methane-rich to extremely methane-rich coalbeds and have strong ability to adsorb and store CBM. Coal seam gas shows generally, and the measured gas-bearing property is good. Low-rank CBM accounts for the majority of CBM resources in the basin. According to Langmuir volume, the gas provinces are classified into four types of blocks, i.e., CBM-poor (< 8 m3/t), CBM-bearing (8–15 m3/t), relatively CBM-rich (15–20 m3/t) and CBM-rich (> 20 m3/t). The relatively CBM-rich blocks cover block of well Qing 1 to Qi 8, Changji–Urumqi–Fukang area and slope belt of northwest margin to basin hinterland; while the CBM-rich blocks include most of eastern Junggar Basin. Since 2005, a series of special exploration and research of CBM have been carried out successively, and significant progress has been made in exploration of deep and shallow combination, conventional (gas) and unconventional (gas) combination. Recently shallow CBM exploration has achieved gas extraction at Dahuangshan coal mine, industrial gas flow wells in western Baiyanghe, and breakthrough of deep CBM exploration in Baijiahai area has been made, which confirmed the great development potential of low-rank CBM. The southern margin and the east of Junggar Basin have become the new frontier of low-rank CBM exploration in China.

Pore Characteristics and Methane Adsorption Capacity of Different Lithofacies of the Wufeng Formation–Longmaxi Formation Shales, Southern Sichuan Basin

ABSTRACT: The significantly different geological processes experienced by the shales in the southern Sichuan Basin provide a means for comparing their pore characteristics and their supercritical m...

Investigation of the fractal characteristics of adsorption‐pores and their impact on the methane adsorption capacity of various rank coals via N2 and H2O adsorption methods

AbstractCoal seam is a sedimentary body with complex pore system. The gas adsorption property of coal is greatly determined by the adsorption‐pores (&lt;100 nm), and the fractal dimension can be used an index to estimate the impact of the adsorption‐pores on the methane adsorption capacity of various rank coals. In this paper, low‐temperature N2 adsorption and H2O adsorption methods were used to study the adsorption‐pores structure and its fractal features. The results show that the development of adsorption‐pores closely depends on the coalification, and the degree of pore development exhibits a U‐shaped trend with increasing coal rank. Additionally, the pore size distributions of coal samples from N2 adsorption analysis and H2O adsorption analysis are similar, especially for samples LH7 and WLH8. Fractal analysis indicates that D2(N2) (0.5 &lt; P/P0 &lt; 1) can more accurately characterize the fractal features of adsorption‐pores than D2(H2O), which may be a result of the significant coal‐H2O interaction. Moreover, D2(N2) has stronger correlations with the coal pore parameters. With the increase in D2(N2), the Langmuir volume first decreases and then increases, which is probably associated with the competition effect of the pore structure and surface irregularity of coal. When D2(N2) &lt; 2.7‐2.8, the pore structure plays a key role, while for D2(N2) &gt; 2.7‐2.8, the influence of the specific surface area is more prominent. The equilibrium moisture content of the coal samples also has a positive correlation with D2, except for low‐rank coal sample YZG2 due to the presence of a large amount of oxygen‐containing functional groups, which increases its water‐holding capacity.

The effects of pore structure on wettability and methane adsorption capability of Longmaxi Formation shale from the southern Sichuan Basin in China

The lower Silurian Longmaxi Formation shale in the Sichuan Basin is one of the most promising shale gas plays in China. Pore structure has a significant impact on hydrocarbon migration within shales. This study conducts systematic experiments to analyze the pore structure, wettability, and methane adsorption capacity of the Longmaxi Formation shale samples from the southern Sichuan Basin. The pore-size distributions obtained from N2 adsorption, high-pressure mercury intrusion porosimetry, and statistical analysis of representative field emission–scanning electron microscopy photographs of organic matter (OM) are compared to evaluate the contribution of OM pores to total pore spaces. Shale wettability was determined by contact angle measurements and spontaneous imbibition experiments. The results reveal that these samples could be divided into three wettability categories: more water-wet samples Z1, more oil-wet samples Z4, and intermediate-wet samples Z2 and Z3. Although samples Z1 and Z4 have similar total organic carbon (TOC) contents, OM pores within sample Z4 have a larger average pore size and occupy a greater proportion of the total pore spaces compared with sample Z1, whereas inorganic pores contribute more to the total pore spaces of sample Z1. Sample Z4 has a larger methane adsorption capacity than sample Z1 with a higher Brunauer–Emmett–Teller (BET) surface area, which may be caused by the difference in their OM pore types. Samples Z2 and Z3 with less TOC content have lower porosities and BET surface areas as well as lower methane adsorption capacities. Consequently, the pore structure significantly affects the wettability and methane adsorption capacity of the Longmaxi shale.

Adsorptive removal of gaseous formaldehyde at realistic concentrations

Due to analytical reasons, adsorption capacity is often determined at very high concentrations which is not representative of a real environment. The aim of this work is to provide experimental data of formaldehyde adsorption capacity at realistic levels (∼164 ppb) thanks to a near real-time powerful formaldehyde analyser recently developed in our laboratory. Gaseous formaldehyde breakthrough experiments were conducted on a broad spectrum of materials including carbon, zeolites, metal organic framework and mesoporous silica in order to determine their adsorption capacity. Among these materials, HKUST-1 exhibited the highest adsorption capacity (504 μg/g ads) followed by MgZSM-5 (35 μg /g ads), SBA-16 (29 μg/g ads), ZSM-5 (10–26 μg/g ads) and Carbopack® B (4 μg/g ads). In the case of ZSM-5 zeolites, the results revealed that formaldehyde adsorption was related to their aluminium content. The presence of aluminium implies more bridging hydroxyl groups Si-(OH)-Al that act as Brønsted acid sites interacting with formaldehyde molecules. Despite the moderate adsorption capacity of ZSM-5 zeolites, they can be considered as promising candidates for gas analysis applications, for example where a good analytical blank is essential for accurate measurements.