Thermal Evolution Process Research Articles

Satellite Observations of Wind Wake and Associated Oceanic Thermal Responses: A Case Study of Hainan Island Wind Wake

The wind wake on the lee side of Hainan Island in the winter covers the southwest entrance of Beibu Gulf (or Gulf of Tonkin) and is essential to regional ocean dynamics. Using multiple satellite observations including advanced synthetic aperture radar (ASAR), we revisited the wake process during the winter of 2011. Asymmetric oceanic thermal responses were found with a warm band expanding northwestwardly while a cold tongue formed to the southeast. Combining satellite observations, model simulations, and reanalysis data, heat advection terms (ADV) are reconstructed and compared to air-sea heat flux terms. The observed thermal evolution process across the wake footprint is closely related to the balanced spatial variability from the Ekman ADV, the barotropic geostrophic ADV, and the latent heat flux (LHF), which are all on the order of 10−5 K·m·s−1. Specifically, the Ekman ADV tends to heat the northwestern side of the wake and cool the southeastern side, while the geostrophic ADV compensates with the Ekman ADV across the wake footprint. This study reveals detailed oceanic responses associated with the wind wake and clarifies the contribution of ADV to the asymmetric spatial thermal variabilities. The identified role of heat advection on a sub-seasonal timescale may further benefit the understanding of regional oceanic dynamics.

Geochemical Characteristics of Shale Gas in the Silurian Longmaxi Formation, Jiaoshiba Area, Southeast Sichuan Basin, China

On the basis of geochemistry tests, in combination with comparative studies of the Weiyuan-Changning shale gas field in the south Sichuan Basin and typical shale gas fields in North America (such as Barnett and Fayetteville), the geochemical characteristics of the Lower Silurian shale gas in the Jiaoshiba area were studied. The results show that (1) the average RO value of Longmaxi shale in Jiaoshiba area is about 2.65%, which is at the dry gas stage. The content of CH4ranges from 94.02% to 98.95%, and the contents of ethane and propane are lower. The weight anomaly average values of δ(13C1) and δ(13C2) are −30.18‰ and −35.45‰, respectively. (2) Non-hydrocarbon gases are dominated by CO2 and N2. The CO2 in the Longmaxi shale gas in the Jiaoshiba has three origins: the thermogenic CO2, the abiogenic CO2, and the biogenic CO2. The N2 in the Longmaxi shale gas comes from the released N2 during the thermal evolution process of sedimentary organic matter under the control of maturity and kerogen type. (3) The ...

Distribution and genesis of mercury in natural gas of large coal derived gas fields in China

Abstract The mercury content in natural gas samples from more than 500 gas wells in eight large gas bearing basins of China was tested, mercury release experiments on two coal samples from different areas were conducted, and the mercury content of 11 coal samples from different gas wells of Ordos Basin was tested. The mercury distribution of the coal derived gas has three features: The first is that mercury content of coal derived gas is generally much higher than that of oil derived gas, the second is that the coal derived gases from different fields vary widely in mercury content, the third is that the mercury content in coal derived gas increases with the increase of production layer depth. Mercury in coal derived natural gas mainly originates from the source rock. Besides three evidences, namely, coal derived gas mercury content is much higher than that of oil derived gas, mercury content of gas with high carbon dioxide content decreases with the increase of carbon dioxide content, and the coal bearing strata have the material base to generate natural gas with high mercury content, the pyrolysis experiment of two coal samples show that coal can produce natural gas with high mercury content during the process of thermal evolution. The mercury content of coal derived natural gas is controlled mainly by the temperature of source rock and the sulfur environment of reservoir. According to lithospheric material cycling process and oil-gas formation process, the formation of mercury in coal derived gas can be divided into four stages, transportation and deposition, shallow burial, deep burial, and preservation and destruction.

A Quantitative Evaluation of Shale Gas Content in Different Occurrence States of the Longmaxi Formation: A New Insight from Well JY‐A in the Fuling Shale Gas Field, Sichuan Basin

Comprehensive quantitative evaluation of shale gas content and the controlling factors in different occurrence states is of great significance for accurately assessing gas‐bearing capacity and providing effective well‐production strategies. A total of 122 core samples from well JY‐A in the Fuling shale gas field were studied to reveal the characteristics of S1l shale, 15 of which were selected to further predict the shale gas content in different occurrence states, which are dependent on geological factors in the thermal evolution process. Geological parameters were researched by a number of laboratory programs, and the factors influential in controlling shale gas content were extracted by both PCA and GRA methods and prediction models were confirmed by the BE method using SPSS software. Results reveal that the adsorbed gas content is mainly controlled by TOC, Ro, SSA, PD and pyrite content, and the free gas content is mainly controlled by S2, quartz content, gas saturation and formation pressure for S1l in well JY‐A. Three methods, including the on‐site gas desorption method, the empirical formula method, and the multiple regression analysis method were used in combination to evaluate the shale gas capacity of well JY‐A, all of which show that the overall shale gas content of well JY‐A is in the range of 2.0–5.0 m3/t and that the free gas ratio is about 50%, lower than that of well JY‐1. Cause analysis further confirms the tectonics and preservation conditions of S1l in the geological processes, especially the influence of eastern boundary faults on well JY‐A, as the fundamental reasons for the differences in shale gas enrichment in the Jiaoshiba area.

Mapping and Characterizing Thermal Dilation of Civil Infrastructures with Multi-Temporal X-Band Synthetic Aperture Radar Interferometry

Temperature variation plays a significant role in the long-term structural behaviour of civil infrastructures, but very few quantitative studies have measured and analysed the infrastructures’ global thermal dilation because of their large sizes and geometric complexities. The modern Differential Synthetic Aperture Radar Interferometry (DInSAR) technique has great potential in applications of their thermal dilation mapping and characterization due to the techniques’ unique capabilities for use in large areas, with high-resolution, and at low-costs for deformation measurements. However, the practical application of DInSAR in thermal dilation estimation is limited by difficulty in the precise separation from the residual topographic phase and the trend deformation phase. Moreover, due to a lack of thermal dilation characteristics analyses in previous studies, the thermal dilation mechanisms are still unclear to users, which restricts the accurate understanding of the thermal dilation evolution process. Given the above challenges, an advanced multi-temporal DInSAR approach is proposed in this study, and the effectiveness of this approach was presented using three cases studies concerning different infrastructure types. In this method, the coherent, incoherent, and semantic information of structures were combined in order to refine the detection of point-like targets (PTs). Interferometric subsets with small temporal baselines and temperature differences were used for high-resolution topography estimation. A pre-analysis was adopted to determine the transmission direction, spatial pattern, and temporal variation of the thermal dilation. Then, both the traditional least squares estimation and our robust coherence-weighted least squares regression analysis were performed between the time series displacements and the corresponding temperatures to quantitatively estimate the thermal dilation model. The results were verified in terms of the estimated linear thermal dilation coefficient, which indicates the greater reliability of our method. Furthermore, the thermal dilation characteristics of different civil infrastructure types were analysed, which facilitates a greater understanding of the thermal dilation evolution process of civil infrastructures.

Simulation for the dissolution mechanism of Cambrian carbonate rocks in Tarim Basin, NW China

Abstract Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution in the Tarim Basin. The results showed that mineral composition and reservoir space type control selective dissolution. In the carbonate rock strata with high calcite content, the calcite is likely to dissolve first to form secondary dissolution pores; gypsum and anhydrite in the carbonate rock can be dissolved to form mold pores in contemporaneous and penecontemporaneous stages. Porous carbonate has mainly enlargement of matrix pores, with porosity and permeability increasing correspondingly, but not obviously. In comparison, dominant channels for fluid are likely to occur in fractured carbonate or porous carbonate forming cracks under high pressure, resulting in a relative reduction in the dissolution volume, but great increase of permeability. With the rise of temperature and pressure, corrosion ability of acid fluid to carbonate rock increases first and then decreases, there exists an optimum range of temperature and pressure for dissolution, which corresponds to the buried depth of 2 250−3 750 m of the Cambrian. Considering reservoir characteristics of the study area, it is concluded that calcite in the penecontemporaneous period is the material basis for the development of dissolution pore, and carbonate rock were mainly dissolved by early atmospheric fresh water, superimposed and reformed to form high quality reservoirs by multiple acid fluids including deep hydrothermal fluid and acid fluid generated during the process of organic thermal evolution under burial condition.

Calcination-induced changes in structure, morphology, and porosity of allophane

Abstract Allophane with an Al/Si molar ratio of 1.6 was hydrothermally synthesized, followed by calcination at defined temperatures up to 1300 °C. The heated products were then characterized using a combination of techniques including X-ray diffraction, Fourier transform infrared spectroscopy, thermal analyses, nuclear magnetic resonance, transmission electron microscopy, and N2 physisorption. In allophane, the imogolite local structure (ImoLS) had a relatively low thermal stability, and the adsorbed water was removed at a low temperature. Five major steps were outlined for the thermal evolution process of allophane. (i) At 200 °C or lower, the loss of adsorbed water and partial dehydroxylation of Si OH accompanying with the formation of Si O Si resulted in the loss of ImoLS. (ii) As the temperature rose, further dehydroxylation of Si OH as well as disassociation of Al OH occurred, leading to decreases in the specific surface area and porosity due to the continued agglomeration of hollow spherules, whereas the spherical morphology of allophane was largely retained. (iii) At approximately 500 to 900 °C, the disconnection of AlO octahedra and SiO tetrahedra caused increased disintegration of the allophane structure and formation of amorphous alumina and silica. (iv) At approximately 1000 °C, nanosized mullite was crystallized by the reaction between the yielded amorphous alumina and silica. (v) Finally, further growth of the already-formed mullite crystals and formation of cristobalite occurred, with the consumption of excess silica.

Thermal evolution of lithium ion substituted cesium-based geopolymer under high temperature treatment, Part I: Effects of holding temperature

In this paper, a high temperature treatment procedure was designed to evaluate the effect of holding temperature on thermal evolution process of Li+ substituted Cs-based geopolymer (Cs0.7Li0.3GP), including the thermal analysis, phase composition and microstructure evolution. With rising of holding temperature, amorphous unheated Cs0.7Li0.3GP gradually transformed into a multiphase system during the high temperature treatment process, which consisted of pollucite (CsAlSi2O6), spodumene (LiAlSi2O6) and amorphous glass phase. In the multiphase system, Cs+ ions were in the form of pollucite grains, while Li+ ions were in the form of spodumene nanocrystallines distributed in amorphous matrix. The pollucite grains gradually coarsened with rise in holding temperature, and the densification of the resulting products were also improved synchronously, which were related to the presence of amorphous glass phases. The amorphous glass phase would be in a molten state when holding temperature over 800 °C. And the presence of molten amorphous phase would make the mass transfer process easier, which could contribute to the growth of the crystal grains and the elimination of the pores.

Pore characteristics and formation mechanism of high-maturity organic-rich shale in Lower Cambrian Jiumenchong Formation, southern Guizhou

In order to investigate pore characteristics and formation mechanism in the high-maturity organic-rich shale of Lower Cambrian Jiumenchong Formation in southern Guizhou, the pore structure, pore type and storage properties are well studied through the rock thin section, total rock X-ray diffraction, low-temperature nitrogen adsorption, high pressure mercury injection-adsorption test, helium porosity test, argon ion polishing-scanning electron microscope, thermal evolution and pore evolution history reconstruction, and based on the diagenesis and compaction as well as thermal evolution process, a microscopic pore formation and evolution model of high-maturity organic-rich shale are established. The result shows that the high-maturity organic-rich shale of Jiumenchong Formation has the average total specific surface area of 12.66 m2/g and the total pore volume of 11.54 × 10−3 cm3/g, and the total specific surface area have a positive correlation with total pore volume; the total specific surface area and the total pore volume are slightly lower compared with the Lower Silurian shale. The pores are dominated by micropores and mesopores, while macropores are very rare. The pores of the organic-rich shale mainly are organic pores with small diameter usually less than 30 nm, and the pore boundary form is irregular, the inorganic mineral pores are not developed. Compared with the Silurian shale, the shale has poorer reservoir property, the average porosity is only 2.80%; the horizontal permeability is 1–3 times of the vertical permeability, indicating the horizontal lamellations are not developed. The formation and evolution of pores in high-maturity organic-rich shale is jointly influenced by the evolutionary process of intergranular pores of inorganic mineral under the control of the diagenesis and compaction, the organic pore formation process in the hydrocarbon generation-oil formation-oil and gas transformation sequence under the control of thermal evolution, and the natural gas loss-supply equilibration process under the condition of later pore preservation.

Numerical modeling of the autumnal thermal bar

Abstract The autumnal riverine thermal bar of Kamloops Lake has been simulated using atmospheric data from December 1, 2015, to January 4, 2016. The nonhydrostatic 2.5D mathematical model developed takes into account the diurnal variability of the heat fluxes and wind on the lake surface. The average values for shortwave and longwave radiation and latent and sensible heat fluxes were 19.7 W/m2, − 95.9 W/m2, − 11.8 W/m2, and − 32.0 W/m2 respectively. Analysis of the wind regime data showed prevailing easterly winds and maximum speed of 11 m/s on the 8th and 19th days. Numerical experiments with different boundary conditions at the lake surface were conducted to evaluate effects of variable heat flux and wind stress. The results of modeling demonstrated that the variable heat flux affects the process of thermal bar evolution, especially during the lengthy night cooling. However, the wind had the greatest impact on the behavior of the autumnal thermal bar: The easterly winds contributed to an earlier appearance of the thermal bar, but the strong winds generating the intensive circulations (the velocity of the upper lake flow increased to 6 cm/s) may destroy the thermal bar front.

Experimental Demonstration of the Relational Character of Time in Natural Processes; Concept of Time in the Relational World

Using new experimental techniques, studies of thermal evolution processes are performed in systems, which are beyond the description of theoretical physics. Evolution process is characterized by braking symmetries in time and in space and by violations of conservation laws of energy and momentum. It is shown experimentally that the superposition principle is not valid for electromagnetic (EM) fields interacting with material objects the Poynting vector of the external field is the source of changes in the properties and structure of the irradiated object the thermal hysteresis loop presents a record of the process in two locations. The interaction of material objects through common EM field, which is carrying the contributions of the hysteresis effects in the parts of each interacting object, can be described only by the concept of a process that is characterized by its dependence on the huge number of correlated influence factors. The flux of Poynting vector of common EM field through boundary surface of the irradiated object is the reason for the development of the thermal process inside it, thus realizing the interrelation of one to all in the Leibniz relational World. Defining the concept of time as a reference process in experiments, in which the records of the states of one of the process are performed in terms of the states of the reference process in some material detector, we obtain the concept of time as a natural development of the basic principles of G. W. Leibniz, E. Mach, A. Einstein, W. Pauli, D. Kleppner.nbsp

Thermal behavior and Raman spectral characteristics of step-heating perhydrous coal: Implications for thermal maturity process

Perhydrous coal (PHC) had been widely investigated; however, a systematic research on the relationship between the structure of PHC and its thermal reactivity was rarely reported in the previous studies. The PHC was widely developed in the Carboniferous-Permian coal-bearing strata in the northern and eastern regions of the Huainan coalfield. In this study, we chose No. 13-1 PHC as the research object. Based on the macroscopic observation of No. 13-1 PHC of the borehole #9-3 and its logging response, a typical PHC sample was selected and pyrolyzed using a thermogravimetric analyzer (TGA) to acquire a set of coal samples after pyrolysis with wide range of random vitrinite reflectance (% VRo) from 0.86 to 7.79%. The thermal evolution process of PHC before and after pyrolysis was investigated by atomic force microscopy (AFM) and Raman spectroscopy. Research results show that: 1) in the experimental temperature range, the reflectance (VRo) range of PHC varied greatly; 2) with the increase of pyrolysis temperature, the Raman spectra of PHC changed significantly in the D band of disordered structure and the G band of ordered structure and the orderliness of its macromolecule particle arrangement was increasing gradually; 3) the relationship between the thermal reactivity of PHC and its Raman structure parameters was established, the FWHM of G-band can be used as indicators of the degree of thermal evolution of PHC; 4) compared with the G FWHM of normal coal with different rank, the thermal reaction temperature of PHC was advanced. Under the premise of comparable reaction temperature, the thermal maturity of PHC was gradually higher than that of bituminous coal, and slightly lower than anthracite, indicating that the actual PHC thermal maturity was suppressed by a higher amount of hydrogen.

Effects of Na+ substitution Cs+ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer

AbstractAs part of a series of studies, effects of Na+ substitution on the thermal evolution of cesium‐based geopolymers on heating were studied. A series of sodium‐substituted cesium‐based geopolymers, Cs(1−x)NaxGPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG‐DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs(1−x)NaxGPs was not completely amorphous after the substitution of Na+ and the crystallinity of Cs(1−x)NaxGPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs(1−x)NaxGPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi2O6) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs+ were replaced maybe owing to the role of Na+ in the nucleation process of pollucite. Two forms of Na+ present in the final products: A small portion was present in the pollucite grains due to Na+ partial occupied the crystallographic sites of Cs+; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs(1−x)NaxGPs ceramics increased from 4.80×10‐6 K−1 (x=0) to 7.26×10−6 K−1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite.

On the meaning of peak temperature profiles in inverted metamorphic sequences

Inverted metamorphic sequences (IMS) are common features of main thrust systems on Earth. They exhibit an upwards continuous increase in peak temperature conditions and thereby constitute evidence of the close relationship between the thermal field evolution and tectonic processes. Heat advection and shear heating are known to allow the formation of such metamorphic signatures. Heat diffusion also plays an important role in temperature distribution on both sides of the thrust. Other advection processes such as erosion or accretion may also cause a local peak temperature inversion. Each one of these processes therefore affects the thermal field around the thrust. However, despite the crucial importance of all these processes for the interpretation of the inverted peak temperature signatures, their respective influences have never been quantified and compared all together. To address this issue, we propose an innovative coupled approach. (i) We use two-dimensional numerical models that simulate various thrust systems, allowing for a wide diversity of setups. To illustrate this study, we focus on intracontinental thrust systems for which all processes listed are likely to play a key role in the thermal evolution. We perform a parametric study including kinematic settings (i.e. convergence, erosion and accretion), thermal properties, mechanical strength and heat sources. (ii) Dimensionless numbers based on parameters are used to quantify the relative contributions of each process to the thermal budget evolution. Hence, the three thermal processes (i.e. heat diffusion, heat advection and shear heating) are compared with each other via three dimensionless combinations of the Peclet and Brinkman numbers: RDif, RAdv and RPro, respectively. Erosion and accretion are compared separately, based on a fourth dimensionless number Rea. (iii) We analytically examine the inverted peak temperature recorded along profiles that are perpendicular to the thrust zone defined in our numerical experiments. Each peak temperature profile presenting an inversion can then be characterized by a function of approximation involving six meaningful parameters: the location μFF and width σFF of the maximum peak temperature inversion, the characteristic peak temperature Tcte and gradient GLB beneath the inversion zone, and the inversion-related contrasts in the peak temperature ΔT and gradient ΔG. This coupled approach, linking numerical modelling and analytical treatment, allows to quantitatively interpret IMS in terms of the processes involved. The application of our method to intracontinental thrust systems demonstrates that shear heating and erosion support significant inversions, but that the relative contributions of each process have meaningful consequences. Our results reveal that competition between shear heating and heat diffusion on the one hand, and between erosion and accretion on the other hand have a high impact. In particular, the variability in the rock's mechanical strength strongly influences the features of peak temperature inversions. Consequently, none of these processes can be ignored. Our results highlight the major importance of the rheology of rocks in the thermal evolution of shear zones. Finally, our methodology is not only restricted to the analysis of numerical data but also constitutes a way of broad interest to analyse peak temperature signatures around any shear zone.

Application of a novel approach to assess the thermal evolution processes associated with the disposal of high-heat-generating waste in a geological disposal facility

The widely accepted solution for the long-term management of higher activity radioactive waste is disposal in a suitably engineered facility, located deep underground. A geological disposal facility (GDF) consists of a series of engineered and natural barriers preventing or inhibiting the release of radioactivity. These barriers include: the radioactive wasteform, the waste disposal container, the buffer material to protect the container and the natural barrier provided by the rocks in which the facility is constructed. This multi-barrier system aims to isolate the waste and contain the harmful effects of the radioactivity on humans and biota in the surface environment.The engineered barrier system (EBS) used in a GDF can include buffers based on cement and clay-based materials. The choice of buffer can have significant implications for the disposal system; the heat must be managed such that the properties of the buffer are not compromised to the extent that it cannot deliver the required level of safety. One of these materials is bentonite, usually rich in sodium montmorillonite, selected for its swelling properties and low hydraulic conductivity when saturated. In the presence of significantly elevated temperatures sodium montmorillonite can undergo mineral alteration, reducing the swelling properties of this material. This paper describes an efficient approach to assess strategies for meeting a maximum temperature constraint placed on either the buffer or geosphere surrounding the waste container. In preparation for designing and building a GDF, it is important, for the purpose of robust planning, to understand the important factors, and uncertainties, affecting the maximum temperature. The objective of this work is to inform the future emplacement strategy to enable: appropriate decay storage times; acceptable waste package loading and spatial configurations of the packages to be determined, to thus enable high-heat-generating waste to be safely disposed in a GDF.

Understanding Battery Failure: A Multi-Scale and High-Speed X-Ray CT Approach

The safety of Li-ion batteries is of upmost importance in particular for demanding applications such as electric vehicles and other mission critical systems. The thermal response of a cell is one of the most important characteristics to understand when assessing the safety of a cell design, as witnessed by recent high profile failures1, 2. However, there is limited understanding of the dynamic mechanisms associated with thermal runaway. X-ray tomography has become a widely used technique for 3D imaging of materials and devices for electrochemical energy storage and conversion. Two of the major advances in tomography techniques in recent years are the reduction in tomogram acquisition time and the increased spatial resolution. In this study, high speed synchrotron X-ray CT of commercial Li-ion batteries during operation and failure was performed in beam-lines ID15A and ID19 at The European Synchrotron (ESRF). Tomograms were captured at a rate of up to 2.5 Hz allowing us to study some of the most rapid failure mechanisms including those associated with thermal runaway in 3D3. Simultaneous thermal imaging and X-ray tomography allowed structural and thermal evolution processes to be tracked dynamically. We have demonstrated the capability to track electrode layer delamination 4, cracking, and gas evolution processes occurring at multiple time and length scales. Combined with multi-scale post-mortem tomography analysis our recent work has provided insight into the failure of battery materials from the cell scale down to the particle scale. Features which may be indicative of temperatures reached and reaction pathways during failure are identified via inspection of electrode microstructures. For example, surface layers of transition metals on electrode particles are seen; suggesting numerous exothermic reduction steps in the presence of electrolyte. Significant changes in particle morphology are also observed which can affect the rate of heat generation and onset temperatures of thermal runaway. This combined high-speed and multi-scale tomography approach uses cutting-edge imaging techniques to explore failure mechanisms which were previously not understood. New insights into the structural and thermal dynamics leading up to and during thermal runaway and failure are achieved. The thermal response and catastrophic outcomes observed on the macro scale are linked to the structural properties of active materials on the micro-scale, revealing scope for further investigations on the impact of particle morphology on failure mechanisms of Li-ion cells.

Numerical study on hydraulic fracturing in tight gas formation in consideration of thermal effects and THM coupled processes

This paper introduces and explicates a new thermal module that has been developed to study numerically the heat transport in a hydraulic fracture and heat exchange between the fracture and the surrounding reservoir rocks, as well as the THM coupled processes that take place during hydraulic fracturing in a tight gas reservoir. The new module was embedded in the simulator FLAC3Dplus and validated by comparison with several analytical examples. In this paper the new module was subsequently used to model the stimulation job that was executed in a tight gas reservoir (for anonymity reasons only known as X6) in the Northern German Basin. Its basis is the history-matching of the in-situ measured wellhead pressure. The paper presents the exceptional ability of the new thermal module to simulate the entire thermal evolution process during hydraulic fracturing, including a period of temperature recovery towards the original geothermal reservoir temperature (also termed temperature warm back) after shut-in. Further observations by this paper include the significant temperature increase at the fracture front during treatment. This is caused by a delay in the arrival of the fracturing fluid at the fracture tip. In addition, the paper draws a comparison between two simulations: one executed with a thermal module to investigate the THM coupled effects on fracture development and the other without taking the thermal effects into consideration. The basis for the comparison is that the models use (in terms of geometry and stratigraphy) identical mechanical, hydraulic and thermal parameters in both simulations. Results show that the cooling effect of the injection fluid leads to contraction of the rock formations thereby causing them to experience an extra load of tensile stress. In this regard, the hydraulic fracture will easily propagate in the direction of minimum horizontal stress (where rock stress also seems to have decreased remarkably). Finally, the paper observed that simulations carried out using the new thermal module achieved a wider but shorter fracture than that obtained in simulations without consideration of heat effects. Nevertheless, the fracture heights in both cases were almost identical due to the existence of caprocks with similar integrity. Trends indicate that the simulation without thermal module caused a greater leak off volume at the end of the operation, since the fracture surface attained in this case was larger.

The magmatic activity mechanism of the fossil spreading center in the Southwest sub-basin, South China Sea

Petrogeochemical data indicate that after the end of seafloor spreading, residual magmatic activity still exists in the deep basin of the South China Sea. By using different viscous structure models beneath the fossil spreading center of the Southwest sub-basin we simulated the amount of melt produced, the length of the melting period, and the thermal evolution process in terms of geothermics and the buoyant decompression melting mechanism. We compared the results of our model with observed heat flow, seismic, and petrogeochemistry data. The results show that depletion buoyancy induced by buoyant decompression melting plays an important role in the melting process, while retention buoyancy, thermal buoyancy, and viscous shear force have only a weak influence on the melting process. From the length of the melting period, we determined that for the three viscous structures models the magmatic activity lasted about 5, 12, and 15 Ma. Under the effect of buoyant depression melting, local high-temperature areas will develop under the basin, which can explain the low-velocity layer detected by seismic exploration in the middle and upper lithosphere of the Southwest sub-basin. We also simulated the possible lithology distribution beneath the fossil spreading center with the physical conditions of different viscous structure, different temperature structure, and different melting fraction, which provided a greater understanding of the rock petrogeochemical data of the deep sea basin in the South China Sea.

Experimental and analytical analyses of the thermal conductivities and high-temperature characteristics of silica aerogels based on microstructures

An analytical heat transfer model based on scanning electron microscopy, Brunauer–Emmett–Teller and pycnometry measurements and a 3D random diffusion-limited cluster–cluster aggregation structure is proposed to calculate the temperature-dependent microstructural parameters and thermal conductivities of silica aerogels. This model is a pure prediction model, which does not need experimentally fitted empirical parameters and only needs four measured structural parameters as input parameters. This model can provide high-temperature microstructural and thermophysical properties as well as theoretical guidelines for material designs with optimum parameters. The results show that three stages occur during the thermal evolution processes of the aerogel structure with increasing temperature from 300 to 1500 K. The current analytical model is fully validated by experimental data. The constant structure assumptions used in previous heat transfer models are found to cause significant errors at higher temperatures as the temperature-dependent structure deformation significantly increases the aerogel thermal conductivity. The conductive and total thermal conductivities of silica aerogels after high-temperature heat treatments are much larger than those with no heat treatment.

Preparation of SiO2-CuO-CeO2 Composite Powders and Its Thin Film Templated with Oxalic Acid

Silica-based ceramic-matrix composites have shown promise as advanced materials for many applications such as chemical catalysts, ceramics, pharmaceuticals, and electronics. <TEX>$SiO_2$</TEX>-CuO-<TEX>$CeO_2$</TEX> multi-component powders and their thin film, using an oxalic acid template as a chelating agent, have larger surface areas and more uniform pore size distribution than those of inorganic acid catalysts. <TEX>$SiO_2$</TEX>-CuO-<TEX>$CeO_2$</TEX> composite powders were synthesized using tetraethylorthosilicate, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate with oxalic acid as template or pore-forming agent. The process of thermal evolution, the phase composition, and the surface morphology of these powders were monitored by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectrometry (EDXS). The mesoporous property of the powders was observed by Brunner-Emmett-Teller surface (BET) analysis. The improved surface area of this powder template with oxalic acid was <TEX>$371.4m^2/g$</TEX>. This multi-component thin film on stainless-steel was prepared by sol-gel dip coating with no cracks.