Nanopore Formation and Structural Changes in Black Shale During the Initial Weathering Stage: A Longmaxi Formation Profile in Northwestern Hunan, China.

Understanding the controls on composition changes and porosity evolution in the critical zone of shale remains a major challenge. The aim of the present study is to develop a model of the changes in mineral compositions, chemical compositions and nanopore formation in shale during the initial weathering stage. To understand these processes, we selected a Silurian shale profile rich in pyrite and organic matter located in South China. Based on X-ray diffraction (XRD) and bulk elemental data, the variations in mineralogical and chemical compositions with depth were studied. To characterize the full pore size spectrum and to gain insight into the nature of secondary pores and their relationship with weathering, nuclear magnetic resonance (NMR) measurements and petrographic observations were combined with scanning electron microscopy (SEM) imaging. The results show that Al and K are enriched slightly, while Ca and Na are depleted in the upper part of the weathering profile. Si, Mn and Ti are relatively stable from the bottom to the top of the profile. Quartz, feldspar, mica, illite and chlorite are the main minerals in the parent rock, and they are relatively stable along the profile. The rock density gradually decreases from 2.6 g/cm³ to 2.1 g/cm³ from the bottom to the top, and the color of the shales changes from black to grayish yellow, but no secondary minerals are detected. The chemical weathering of black shale is dominated by the oxidation of pyrite and organic matter, giving rise to color variation and nanopore formation. The increase in interparticle pores at the nanometer-micron scale is initiated by the dissolution of easily weathered components such as organic matter and pyrite. The removal of clay minerals and tiny particles by groundwater seepage may be the main cause of porosity enhancement during the initial weathering stage. This study suggests that nanoporosity may play an important role in the process of fluid-rock interaction within black shale during the initial weathering stage.

Pore Structure Characterization of Tailing Bed and Dewatering Mechanism at nm-µm Scales Under Shearing.

The preparation of high-density tailings is a prerequisite for cemented paste backfill technology, and the flocculated fine tailings of sealed water leads to challenges in the slurry thickening of tailings. Shearing conditions can compact the micro floc structure to improve the underflow concentration. The nm-µm scales of pore characteristics and connectivity are essential for the dewatering process. The computed tomography (CT) results show that the underflow concentration increases from 62.3 wt% to 68.6 wt% after undergoing rake shearing at 2 rpm, and the porosity decreases from 42.7% to 35.54%. The shearing conditions reduces the spheres and sticks by 43.14% and 43.3%, respectively, from the pore network model (PNM). The seepage flow states were affected by the changes in the pore structure. The maximum surface velocity and the maximum internal pressure decrease after undergoing shearing. Shearing conditions can break the micro floc structures, and the fine particles can fill in the micron-scale pores by gravity and shearing conditions, resulting in the forced drainage of water into the pores. Shearing conditions can break the thickening floc network structures; natural fine particles can fill the micron-scale pores by gravity and shearing conditions. The upward seepage of sealed water along the µm-scale pore channel causes a higher bed concentration. However, the sealed water in the nm-scale pores cannot flow upward due to water cohesion and particle adhesion resistance.

[Spectrum Research on Rheology of High Rank Coal].

Aiming to discuss the change characteristic of macromolecular structures of high rank coal in different rheological conditions, the high rank undeformed coal from southern Qinshui basin and the coal after variable temperature and variable pressure rheology experiments were investigated and analyzed in detail through Fourier transform infrared spectroscopy (FTIR) and laser Raman spectra analysis. The result shows that the texture and composition of different types of rheological coals under different temperature and pressure exhibit significant differences. Experiments of variable temperature and pressure of high rank coal (temperature: 300-400 °C, confining pressure: 50-100 MPa, strain: less than 10% and strain rate: 10(-4)-10(-7) · s(-1) will distort their macromolecular structures and recombine the chemistry structures. When the temperature is 300 °C or 350 °C, the high rank coal generates brittle or brittle-ductile rheology easily, mechanical energy transforms to heat energy, some branches and functional groups with weaker bond energy break and fall off, which split as dissociative micromolecule, with stress degradation as principal role, and stress polycondensation occurs with aromatic, texture increasing. When the temperature is up to 400 °C, ductile rheology of the high rank coal occurs with the secondary defects increasing, mechanical energy transforms to strain energy which helps the early shedding small molecules be embedded or adsorbed in the defect or on the surface of macromolecular preferentially and change the aliphatic and aromatic structures. It is affected by stress degradation and polycondensation progress, and the latter is dominated. The confining pressure and water injection of coal do not have much effect on the macromolecular structure obviously.

[Infrared Spectrum Studies of Hydrocarbon Generation and Structure Evolution of Peat Samples During Pyrolysis and Microbial Degradation].

Hydrocarbon generation and structural evolution would be occurred in the process of from coal-forming material (i. e. peat sample) transforming to the coal. While Fourier Transform Infrared Spectroscopy (FTIR) have a special advantages in analyzing molecular structure of samples. For understanding the characteristics of hydrocarbon generation and structural evolution of coal-forming material during the process of pyrolysis and microbial degradation, based on the physical simulation experiments of closed pyrolysis and anaerobic microbial degradation, the generation potential of thermogenic gas and biogenic gas were studied in this paper, and characteristics of molecular structure evolution and its mechanism was analyzed by FTIR technology. Results show that cumulative gas yields of hydrocarbon gases (mainly for methane) increased with experiment temperature. The gas yield of non-hydrocarbon gas (mainly for CO2) exhibited two peaks at 250 and 375 degrees C. The degradation ability of anaerobe on coal samples weakened with the maturity increasing and there was no gas generation on the pyrolysis samples with maturity from 1.6% to 1.8%. After pyrolysis, the content of hydroxyl in peat sample decreased first and then increased with the pyrolysis temperature increasing. The content of aldehyde carbonyl, methylene and phosphate reduced. The content of aromatic esters decreased with nonlinear. The bone of S-O in stretching vibration appeared after 350 degrees C and its content increased with temperature. This shows that the sulfocompound restrains the activity of methanogenic bacteria. After degradation by anaerobe, the relative content of hydroxyl, aldehyde carbonyl, aromatic esters, methylene and phosphate in peat sample dropped significantly. It is shown that the intermolecular force between these groups weakened.

[Assessment of groundwater quality of different aquifers in Tongzhou area in Beijing Plain and its chemical characteristics analysis].

In order to evaluate the groundwater quality of Tongzhou area in Beijing Plain and to discuss the characteristics of its distribution by the view of hydrochemistry, a total of 151 groundwater samples, collected within study area in the dry period of 2008 according to the geological and hydrogeololgical condition of Tongzhou area, were classified as shallow, middle and deep groundwater, respectively. Based on the data, the groundwater quality was evaluated by the method of F value. The mean and variance of main chemical constituents of groundwater samples were presented. Almost all the quaternary groundwater of Chaobai river pluvial fan belonged to the alkaline water type. The evaluation results based on the analysis results showed that from shallow to deep, the quality of groundwater in Beijing became better. The total areas of groundwater belonging to class IV and V area were 884 km2, 599 km2 and 94 km2 respectively for shallow, middle and deep groundwater. The evaluation results showed that the main exceeding chemical constituents were TDS, hardness, NH4(+), F(-) and total Fe. Most exceeding samples belonged to middle and deep aquifers. The main types of shallow groundwater were HCO2-Ca x Mg- and HCO3 x Cl-Ca x Na x Mg, while the chemical types of mid-deep groundwater were mostly HCO3-Na x Ca- and HCO3 x SO4(2-) -Na x Ca type due to the increased Na(+), SO4(2-) and Cl(-) concentration. Study results showed that the quality of shallow groundwater became worse mainly due to human activities. The deterioration of groundwater quality in mid-deep aquifers was due to both human activities and natural occurrence of poor-quality water.

[Spectrum research on metamorphic and deformation of tectonically deformed coals].

The structural and compositive evolution of tectonically deformed coals (TDCs) and their influencing factors were investigated and analyzed in detail through Fourier transform infrared spectroscopy (FTIR) and laser Raman spectra analysis. The TDC samples (0.7% < Ro,max <3.1%) were collected from Huaibei coalfield with different deformation mechanisms and intensity. The FTIR of TDCs shows that the metamorphism and the deformation affect the degradation and polycondensation process of macromolecular structure to different degree. The Raman spectra analysis indicates that secondary structure defects can be produced mainly by structural deformation, also the metamorphism influences the secondary structure defects and aromatic structure. Through comprehensive analysis, it was discussed that the ductile deformation could change to strain energy through the increase and accumulation of dislocation in molecular structure units of TDC, and it could make an obvious influence on degradation and polycondensation. While the brittle deformation could change to frictional heat energy and promote the metamorphism and degradation of TDC structure, but has less effect on polycondensation. Furthermore, degradation is the main reason for affecting the structural evolution of coal in lower metamorphic stage, and polycondensation is the most important controlling factor in higher metamorphic stage. Under metamorphism and deformation, the small molecules which break and fall off from the macromolecular tructure of TDC are preferentially replenished and embedded into the secondary structure defects or the residual aromatic rings were formed into aromatic structure by polycondensation. This process improved the stability of coal structure. It is easier for ductile deformation of coal to induce the secondary structure defects than brittle deformation.

[FTIR spectroscopic study on the stress effect of compositions of macromolecular structure in tectonically deformed coals].

Fourier transform infrared spectroscopy (FTIR) was applied to the study of the stress effect of compositions of macromolecular structure in tectonically deformed coals. The results showed that in different kinds of tectonically deformed coals, the absorption band of aromatic structure, aliphatic structure and oxygen functional groups nearly consistent in the peak wave number, but the intensity of the peak is different which is justly influenced by different deformation degree and deformation mechanism of tectonically deformed coals under tectonic stress. In the metamorphic and deformed environments of the low, middle and high coal rank, for tectonically deformed coals, with the increasing stress, hydrogen-enriched degree and oxygen-enriched degree decrease, while the degree of ring condensation increases. But there are differences in the change of compositions contents of macromolecular structure. This might indicate that the FTIR could be used in the stress effect of compositions of macromolecular structure in tectonically deformed coals.