High-pressure CO2 Research Articles

Experimental study on the effective measurement of the total homogenization temperature of high internal pressure CO<sub>2</sub>-rich fluid inclusions in orogenic gold deposits: A case study of the Yufeng gold deposit, Eastern Tianshan Orogen

形成于中-深成条件下的造山型金矿的成矿流体属于H₂O-NaCl-CO₂体系，金矿化阶段的石英中发育大量的富CO₂流体包裹体。长期以来，用常规冷热台对其进行显微测温热力学研究时，较高的内压力会造成绝大多数CO₂充填度>0.4的包裹体在尚未达到完全均一状态前就发生爆裂或泄露，导致所测的完全均一温度值明显偏离真实值，甚至无法测得完全均一温度，这制约了对造山型金矿床成矿条件的认知。针对该问题，本文以东天山玉峰金矿床富金矿石中的H₂O-NaCl包裹体（A型）和H₂O-NaCl-CO₂包裹体（AC型）为研究对象，介绍了利用最新型热液金刚石压腔（HDAC-VT型号）测试富CO₂高内压的AC型包裹体完全均一温度的实验流程与结果，并将实验数据与Linkam THMSG600冷热台测得的A型、AC型包裹体的完全均一温度进行了对比分析。实验结果表明，热液金刚石压腔能够有效阻止富CO₂流体包裹体在升温过程中发生爆裂、泄露等非弹性体积改变现象的发生，从而获得有效的完全均一温度。同时，本文还提出了一个新的压力-温度拟合线两线相交法，对热液金刚石压腔所测富CO₂流体包裹体的完全均一温度数据进行校正，以最大程度上减少外压力造成的影响，获得更为接近真实成矿流体的完全均一温度。基于此，获得玉峰金矿床的成矿温度和成矿压力分别为312~343℃和181~268 MPa。本文的实验研究工作显示了热液金刚石压腔在中-深成造山型金矿富CO₂成矿流体的研究领域具有重要应用前景。;The ore-forming fluids of orogenic gold deposits normally belong to a H₂O-NaCl-CO₂ system, and there are usually lots of CO₂-rich fluid inclusions hosted in the quartz at the gold mineralization stage. The trapped fluid inclusions in this type of gold deposit usually have high internal pressures since they are formed at a mid-deep depth in the earth's crust. For a long time, almost all researchers carry out the homogeneous thermomechanical properties study on CO₂-rich inclusions (CO₂ phase filling ratio>0.4) under a 1atm pressure condition. However, when the internal pressure is greater than the external confining pressure, the fluid inclusion will be deformed, such as stretching, leakage and decrepitating, which eventually lead to the measured total homogenization temperature (THT) deviate significantly from the actual value, or even cannot be measured. In order to solve these problems, we choose H₂O-NaCl (A-type) and H₂O-NaCl-CO₂ (AC-type) inclusions in quartz minerals from Yufeng orogenic gold deposit in Eastern Tianshan Orogen as the research object to measure their THTs with high internal pressures by using the latest hydrothermal diamond-anvil cell (HDAC; HDAC-VT type). At the same time, this manuscript compares the THTs obtained by a HDAC-VT with those by a Linkam THMSG600 heating-freezing stage. Our experimental results show that the HDAC can effectively prevent the inelastic volume change of CO₂-rich fluid inclusions during heating process, and consequently obtain an effective THT. In order to minimize the influence of external pressure on the measured THTs and obtain more reliable and accurate metallogenic temperatures, we propose a new two pressure-temperature fitting lines intersection method to calibrate the THTs of CO₂-rich fluid inclusions measured by a HDAC. Based on these improvements, the ore-forming temperatures and pressures of the Yufeng gold deposit are estimated to be 312~343℃ and 181~268MPa, respectively. The experimental work in this paper suggests that the HDAC has an important application prospect in the research field of CO₂-rich fluid inclusions from orogenic gold deposits.

Generation of tail-free short pulses using high-pressure CO2 laser

The spectral linewidth of a transversely excited pulsed CO2 laser is broadened at high working pressures. This phenomenon causes a decrease in the upper-level lifetime such that the pulse width is significantly compressed. Although the tail part of CO2 laser pulses owns a non-negligible proportion of total energy, it has minor effects during the interaction process between photons and materials due to its low amplitude. Thus, it is of great significance to yield the tail part and generate a narrow pulse in most applications. In this study, a continuously tunable pulsed CO2 laser with a low nitrogen proportion in the mixture is developed to generate tail-free short pulses; a minimum pulse width of 30.60 ns with a maximum pulse energy of 481 mJ is synchronously achieved at a pressure of 7 atm, and the estimated peak power is above 15 MW. A numerical simulation is also conducted for comparison with the experimental results. The contribution of the spectral gain toward the compression of the pulse width is discussed in the last section of this paper.

Study on CO<sub>2</sub> gas Hydrate heat cycle for electricity storage system

The expansion of renewable energy power generation is urgently needed to realize a decarbonized society. However, the high cost of butteries used to adjust electricity fluctuations is hindering the expansion of renewable energy power generation. In this study, we aim to develop a new energy storage method for storing excess electricity by using the unique state change of CO2 hydrate. CO2 hydrate is produced at about 0℃ under high pressure of several MPa, and can be dissociated at about room temperature. In the proposed system, the cold and warm heat required for the cooling and heating of CO2 hydrate is obtained from renewable energy. CO2 hydrate absorbs CO2 during its formation and releases high-pressure CO2 hydrate dissociation. Therefore, the pressure in the reaction vessel becomes high after CO2 hydrate dissociation. In this study, an expander is driven by the high-pressure dissociation gas of CO2 hydrate and a generator connected to the expander is operated. The amount of electricity generated in this process will be investigated and compared with the amount of electricity generated when the reaction vessel is filled CO2. The amount of electricity generated was greater when CO2 hydrate dissociated gas was used to generate electricity than when the reaction vessel was filled only with CO2.

Micro-fractures in coal induced by high pressure CO2 gas fracturing

To effectively drain gas from coal seam, many technologies have been developed to fracture the coal which in turn to release the formation stress and increase permeability and finally achieve the desired gas drainage. CO2 gas fracturing is a newly developed technique for coal seam stimulation towards effective gas drainage. This technique can provide radial fracturing from centimeter to meters scales, but the small-scale fracture system that feeds into this radial system, at millimeter to micrometer scale, has not previously been systematically studied for quantifying the matrix damages. This study addresses this deficiency through blast-loading experiments with CO2 on anthracite specimens at overpressures of 120 MPa, 150 MPa and 185 MPa in the in-house novel experimental system. The Field Emission Scanning Electron Microscope (FESEM) images suggest that the cleat system is destroyed, and the intervening matrix effectively pulverized due to the impact load induced by the CO2 blasting. Radial and branching fractures are featured with the process, as typical in high velocity fracturing. The center point is a serious damage mark (DM) that always shows as a shallow pit, and number of smaller broken coal scatter surround the mark. These newly produced fractures are open and zigzag. Based on the observations, it is supposed that the matrix fracturing mechanism by CO2 gas impacting can be described as four consecutive steps: CO2 gas beam destroyed cleat system firstly, and coal broken to millimeter size particles. Meanwhile, CO2 gas jet beam impacting on coal matrix induce a DM and resulting in the matrix’s tensile deformation. Consequently, tri- fracture initiated from the DM and extending radially to different direction. When numerical tri-fracture connected and formed a complex fracture network in which permeability is expected to be significantly promoted for the effective gas drainage.

Unravelling the Mechanism of Intermediate-Temperature CO2 Interaction with Molten-NaNO3 -Salt-Promoted MgO.

The optimization of MgO-based adsorbents as advanced CO2 -capture materials is predominantly focused on their molten-salt modification, for which theoretical and experimental contributions provide great insights for their high CO2 -capture performance. The underlying mechanism of the promotion effect of the molten salt on CO2 capture, however, is a topic of controversy. Herein, advanced experimental characterization techniques, including in situ environmental transmission electron microscopy (eTEM) and CO2 chemisorption by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), transient 18 O-isotopic exchange, and density functional theory (DFT), are employed to elucidate the mechanism of the CO2 interaction with molten-salt-modified MgO in the 250-400°C range. Herein, eTEM studies using low (2-3 mbar) and high (700 mbar) CO2 pressures illustrate the dynamic evolution of the molten NaNO3 salt promoted and unpromoted MgO carbonation with high magnification (<50nm). The formation of 18 O-NaNO3 (use of 18 O2 ) and C16 O18 O following CO2 interaction, verifies the proposed reaction path: conversion of NO3 - (NO3 - → NO2 + + O2- ), adsorption of NO2 + on MgO with significant weakening of CO2 adsorption strength, and formation of [Mg2+ … O2- ] ion pairs preventing the development of an impermeable MgCO3 shell, which largely increases the rate of bulk MgO carbonation.

Optimization of the Appearance Quality in CO2 Processed Ready-to-Eat Carrots through Image Analysis.

A high-pressure CO2 process applied to ready-to-eat food products guarantees an increase of both their microbial safety and shelf-life. However, the treatment often produces unwanted changes in the visual appearance of products depending on the adopted process conditions. Accordingly, the alteration of the visual appearance influences consumers’ perception and acceptability. This study aims at identifying the optimal treatment conditions in terms of visual appearance by using an artificial vision system. The developed methodology was applied to fresh-cut carrots (Daucus carota) as the test product. The results showed that carrots packaged in 100% CO2 and subsequently treated at 6 MPa and 40 °C for 15 min maintained an appearance similar to the fresh product for up to 7 days of storage at 4 °C. Mild appearance changes were identified at 7 and 14 days of storage in the processed products. Microbiological analysis performed on the optimal treatment condition showed the microbiological stability of the samples up to 14 days of storage at 4 °C. The artificial vision system, successfully applied to the CO2 pasteurization process, can easily be applied to any food process involving changes in the appearance of any food product.

New cognition on pore structure characteristics of Permian marine shale in the Lower Yangtze region and its implications for shale gas exploration

Shale of the Middle–Upper Permian Dalong Formation and Gufeng Formation in the Lower Yangtze region is characterized by large thickness, high total organic carbon (TOC), wide distribution and moderate organic thermal evolution degree, so it may be the next important field of shale gas exploration. In order to point out the target and direction of shale gas exploration and development in this region, this paper selects the Dalong Formation and Gufeng Formation shale in the Xuanjing area of Lower Yangtze as the research object to quantitatively describe the development characteristics of shale pores of different scales by means of scanning electron microscopy (SEM), high pressure mercury injection, CO2 and N2adsorption. Then, the fractal dimension of sample pores is calculated by using the FHH (Frenkel–Halsey–Hill) model. Finally, combined with TOC and mineral compositions, the relationship between pore structure and fractal dimension is discussed. And the following research results are obtained. First, dominant lithofacies of Dalong Formation are argillaceous-rich siliceous shale and argillaceous-rich/siliceous mixed shale, which has smaller specific surface area and pore volume, larger average pore diameter. The pore development is mainly controlled by clay mineral content. Dominant lithofacies of Gufeng Formation is siliceous shale, which has a larger specific surface area and pore volume, and smaller average pore diameter. The pore development is controlled by organic matter and brittle mineral content. Second, the influencing factors of fractal dimension can be attributed to the controlling factors of micropore development. The fractal dimension D1of Dalong Formation ranges from 2.4515 to 2.5513 (average 2.5227), and D2ranges from 2.5817 to 2.6578 (averagely 2.6246). The fractal dimension D1of Gufeng Formation ranges from 2.5817 to 2.6578 (averagely 2.6246), and D2ranges from 2.7227 to 2.871 (averagely 2.813). Gufeng Formation shale presents the characteristics of more complex pore structure. Third, the fractal dimension D1is more sensitive to specific surface area, pore development and mineral composition, while D2is more effective in characterizing the average pore diameter. In conclusion, Dalong Formation shale with high D1and D2and Gufeng Formation shale with low D1and high D2can be taken as the favorable exploration targets of Permian marine shale gas in the Lower Yangtze region, and the regional overpressure zones (belts) with weaker structural deformation in hydrocarbon rich sags will be the favorable shale gas exploration targets in this area.

Hybrid two–stage СО2 transcritical mechanical compression–ejector cooling cycle: Thermodynamic analysis and optimization

In the paper, the main results of thermodynamic analysis and optimization of the hybrid two–stage carbon dioxide (СО2) transcritical mechanical compression–ejector cooling cycle are presented. The proposed hybrid cooling cycle contains a two–stage CO2 transcritical mechanical compression refrigeration machine and an ejector cooling machine using refrigerants R245ca, R601b, and R1233zd(E). The operation of the ejector cooling cycle is ensured by using some part of the heat rejected from the compressed superheated CO2 vapor of the mechanical compression refrigeration cycle. The cold obtained in the ejector cooling machine is used for subcooling the high–pressure CO2 vapor after the gas cooler. In addition, the intermediate cooling of the CO2 vapor after the low–pressure stage of the mechanical compression refrigeration cycle is realized by preheating and boiling the refrigerant of the ejector cooling cycle in the additional generator–precooler before entering the main generator–precooler. This paper presents a method for determination of the optimal design parameters and performance of the proposed hybrid cooling cycle. The results showed an increase in efficiency of the two–stage CO2 transcritical mechanical compression refrigeration machine in the proposed cooling system of up to 32.7% compared to the conventional system at transcritical operating conditions with high an environmental temperature.

Ranking novel extraction systems of seedless barberry (Berberis Vulgaris) bioactive compounds with fuzzy logic-based term weighting scheme

In this study, various extraction systems of seedless barberry fruit bioactive compounds (Berberis vulgaris) were ranked using a fuzzy logic-based term weighting scheme (inputs: extraction yield, total phenolic content (TPC), vitamin C content, anthocyanin content, antioxidant activity, time, temperature, pressure). Hot water bath as a control method (C), high-pressure CO2 (HPCD), subcritical water (SCW), and cold press (CP) methods were applied to extract bioactive compounds of the fruit. High-performance liquid chromatography (HPLC) revealed the types of anthocyanins. The results show that the highest and lowest yield were obtained for HPCD and SCW treatment (92.5% and 88.7%, respectively; P > 0.05). The TPC ranged from 214.16 (HPCD) to 457.20 (SCW) mg GAE/100 mL (P < 0.05). The suitable content of TPC was extracted by CP (310 mg GAE/100 mL) in less than 5 min. The most and lowest anthocyanin and vitamin C were obtained by HPCD and SCW extract (P < 0.05). In the control and cold press extracts, Delphinidin-3-O-glucoside and Cyanidin -3-O-glucoside were dominant, while in HPCD extract Cyanidin -3-O-glucoside had the highest value. The antioxidant activity of various extraction methods decreased in the order of SCW > CP > HPCD > C. The experts introduced all of the extraction factors as important to very important (defuzzification score>75). The final results of fuzzy logic showed that CP, HPCD, and Control methods; had a total score above average (score> 50: 70.44, 67.30, and 65.55, respectively) and can be recommended to extract bioactive compounds from barberry depending on the final purpose and the cost-effectiveness.

Effect of Molecular Chain Mobility Induced by High-Pressure CO2 on Crystallization Memory Behavior of Poly(d-lactic Acid)

Recently, the homogeneous crystallization of polymers under CO2 has been investigated systematically, while the effect of CO2 on heterogeneous crystallization such as crystallization memory effect ...

High-pressure cell to study the catalytic behavior of bulk samples and surface deposited mass-selected nanoclusters at atmospheric conditions

A high-pressure reaction cell was developed to study the catalytic activity of supported subnanometer catalysts under atmospheric conditions. With the help of a capillary, the gas composition in the vicinity of the catalyst surface can be analyzed. First, the mean residence time of the gaseous components in the capillary was determined. The dependence of the partial pressures of the reactants on the vertical distance between the capillary and the catalyst was then characterized with the aid of a polycrystalline Pt sample. A Pt(111) surface was then used to validate the experimental setup concerning the CO oxidation under oxygen-rich conditions at a total pressure of 1000 mbar. The partial orders of reaction for CO and O2 agree with values from the literature. The change in the reaction mechanism, which was also described in the literature, could be observed from the temperature-dependent investigation of the CO oxidation. The obtained turn-over frequency and the activation energy at about 660 K agree well with the values obtained in the high-pressure CO oxidation studied in a batch reactor. The efficiency of the experimental setup is demonstrated by examining supported Pt10 clusters since the site density was reduced by a factor of 15 compared to the bulk samples. Taking the Pt site density into account, the sample with the decamers is approximately 5–6 times more active than the Pt(111) surface at a temperature of 673 K. Accordingly, the activation energy for the CO oxidation of 106 kJ mol−1 significantly decreased compared to the value of 132 kJ mol−1 for Pt(111). This finally proves that the high-pressure cell enables the systematic investigation of the size-dependent catalytic behavior of nanoclusters with low degrees of coverage in the future.

Design and performance analysis of compressed CO2 energy storage of a solar power tower generation system based on the S-CO2 Brayton cycle

Two kinds of S-CO2 Brayton cycle tower solar thermal power generation systems using compressed CO2 energy storage are designed in this paper. The energy storage system uses excess solar energy to compress CO2 near the critical point to a high-pressure state for energy storage during the day, and the high-pressure CO2 is heated by a gas-fired boiler or the heat of stored high-temperature molten salt at night, so that it enters the turbine for work and drives the generator to generate electricity. The traditional molten salt heat storage scheme and the proposed compressed CO2 energy storage system model are established with Ebsilon software, and then the equipment selection, structure layout, and parameter design processes are carried out for the energy storage and heating systems. The thermoeconomic and technoeconomic indexes of the three energy storage schemes are calculated under the operating conditions of a typical day. The results show that the efficiency of the combined cycle is higher than that of other organic working fluids when T-CO2 is used as the bottom cycle working fluid. The integrated scheme of compressed CO2 energy storage and auxiliary combustion has the highest average daily efficiency (26.62% on summer solstice and 23.04% on winter solstice) and the lowest initial equipment investment. However, due to the additional cost of natural gas, the scheme has the highest levelized cost of energy (LCOE) at $0.1168/kWh. The LCOE of the integrated scheme of compressed CO2 energy storage and molten salt heat storage was the lowest at $0.1046/kWh.

Converting Captured CO2 Directly into Fuels

The electrochemical conversion of CO2 by the CO2 reduction reaction (CO2RR) is a promising strategy that enables renewable energy to be stored in carbon chemicals and fuels using atmospheric or emitted CO2. Pilot-scale electrolyzers utilizing gaseous CO2 feedstocks can mediate high rates of CO2RR, however, this approach relies on several complex and energy-intensive steps required to produce purified, high-pressure CO2 from carbon capture. This presentation will focus on the direct conversion of aqueous carbon capture solutions (i.e., those rich in bicarbonate anions) into useful chemicals (i.e., CO) over extended periods of time. I will show how to design an electrolyzer that converts liquid bicarbonate feedstocks into carbon products at comparable rates and greater efficiencies than reactors relying on pressurized CO2. Our work demonstrates bicarbonate electrolysis as a practical strategy for storing renewable energy in carbon chemicals while bypassing CO2 separation and pressurization processes in upstream CO2 capture. Figure 1

(Invited) Identifying the Rate-Determining Step in the Electrochemical CO Reduction Reaction

Electrocatalysis powered by renewable energy is expected to play a pivotal role in the global decarbonization process. In particular, electrocatalytic CO2 and CO reduction reactions (CO(2)RR) are widely considered as indispensable components in the valorization of CO2. Much recent research effort has been devoted to the development of efficient and selective catalysts for valuable C2+ products on Cu surfaces, however, many open questions regarding how species in the electrochemical interfaces impact the activity and selectivity remain. In this lecture, we discuss recent efforts in understanding the impact of the surface speciation, adsorbed reaction intermediates and near surface species on the CO(2)RR at the molecular level. The identification of the rate-determining step in the CO(2)RR has been complicated by the lack of rigorous electrokinetic data, from which key mechanistic variables such as the Tafel slopes and reaction orders are determined. Rigorous electrokinetic studies without mass transport limitation show that all C2+ products in the CORR have the common Tafel slope of ~120 mV/dec, and the formation rates are largely invariant with respect to the electrolyte pH on the absolute potential scale. In addition, CO adsorption isotherms determined by in-situ surface enhanced infrared absorption spectroscopy shows that the reaction orders for adsorbed CO are 1st and 0th at low and high partial pressures of CO. Based on these results, we assign the first hydrogenation step of adsorbed CO with adsorbed water, rather than the C-C coupling, as the rate-determining step in the CORR, and propose a reaction mechanism capable of reconciling all experimental observations.

Kinetic and Thermodynamic Analysis of High-Pressure CO2 Capture Using Ethylenediamine: Experimental Study and Modeling

One of the alternatives to reduce CO2 emissions from industrial sources (mainly the oil and gas industry) is CO2 capture. Absorption with chemical solvents (alkanolamines in aqueous solutions) is the most widely used conventional technology for CO2 capture. Despite the competitive advantages of chemical solvents, the technological challenge in improving the absorption process is to apply alternative solvents, reducing energy demand and increasing the CO2 captured per unit of solvent mass. This work presents an experimental study related to the kinetic and thermodynamic analysis of high-pressure CO2 capture using ethylenediamine (EDA) as a chemical solvent. EDA has two amine groups that can increase the CO2 capture capacity per unit of solvent. A non-stirred experimental setup was installed and commissioned for CO2 capture testing. Tests of the solubility of CO2 in water were carried out to validate the experimental setup. CO2 capture testing was accomplished using EDA in aqueous solutions (0, 5, 10, and 20 wt.% in amine). Finally, a kinetic model involving two steps was proposed, including a rapid absorption step and a slow diffusion step. EDA accelerated the CO2 capture performance. Sudden temperature increases were observed during the initial minutes. The CO2 capture was triggered after the absorption of a minimal amount of CO2 (~10 mmol) into the liquid solutions, and could correspond to the “lean amine acid gas loading” in a typical sweetening process using alkanolamines. At equilibrium, there was a linear relationship between the CO2 loading and the EDA concentration. The CO2 capture behavior obtained adapts accurately (AAD &lt; 1%) to the kinetic mechanism.

A path to nano-cellular foams: Constrained cell nucleation and growth in micro-/nano-layered structures

This paper presents a fundamental and experimental investigation of cell nucleation and growth mechanisms in Micro-/Nano-Layered (MNL) polymeric structures with alternating film and foam layers. It was found that the cell morphology in MNL structures is governed by the synergy of two categories of parameter: morphological parameters, i.e., layer thicknesses and the number of layer interfaces, and material parameters, i.e., material stiffness and compatibility. The presence of adjacent film layers can significantly increase cell density through two mechanisms: promoting heterogeneous cell nucleation and preventing cell deterioration. The influence of film layers varied in different layer thickness regions and interface densities, where stiffer and more compatible film layers produced higher cell densities by further enhancing these two mechanisms. Moreover, as a stiffness-enhancing strategy, the crystallization of the Polycarbonate was successfully achieved in MNL structures in a high-pressure CO2 environment for the first time, resulting in more pronounced optimization of cell morphology.

Synergetic effect between curing reaction and CO2 diffusion for microcellular epoxy foam preparation in supercritical CO2

Directly rapid depressurization foaming process has been successfully applied to prepare microcellular epoxy foams using supercritical CO2 as blowing agent. It is found that both curing reaction and CO2 diffusion are crucial for controlling cell morphology. For epoxy of tetraglycidyl-4,4′-diaminodiphenyl-methane (TGDDM) and 4,4-diaminodiphenylsulfone (4,4-DDS) system, the experimental and molecular simulation results displayed that higher CO2 pressure always promotes curing reaction, and CO2 diffusion is more sensitive to pressure at low curing degree, while limited by high curing degree. The foaming experimental results showed that there existed a suitable curing degree range, in which both unsaturated CO2 concentration and curing degree contribute to good cell structure. Higher CO2 pressure can broaden this foamable window. The microcellular epoxy foam with an average cell diameter of 14.6 µm and cell density over 109 cells/cm3 as well as volume expansion ratio of 14.5 has been obtained at 85% curing degree under 22 MPa CO2 pressure.

Experimental study on the adverse effect of gel fracturing fluid on gas sorption behavior for Illinois coal

Hydraulic fracturing is an effective technology for coal reservoir stimulation. After fracturing operation and flowback, a fraction of fracturing fluid will be essentially remained in the formation which ultimately damages the flowability of the formation. In this study, we quantified the gel-based fracturing fluid induced damages on gas sorption for Illinois coal in US. We conducted the high-pressure methane and CO2 sorption experiments to investigate the sorption damage due to the gel residue. The infrared spectroscopy tests were used to analyze the evolution of the functional group of the coal during fracturing fluid treatment. The results show that there is no significant chemical reaction between the fracturing fluid and coal, and the damage of sorption is attributed to the physical blockage and interactions. As the concentration of fracturing fluid increases, the density of residues on the coal surface increases and the adhesion film becomes progressively denser. The adhesion film on coal can apparently reduce the number of adsorption sites for gas and lead to a decrease of gas sorption capacity. In addition, the gel residue can decrease the interconnectivity of pore structure of coal which can also limit the sorption capacity by isolating the gas from the potential sorption sites. For the low concentration of fracturing fluid, the Langmuir volume was reduced to less than one-half of that of raw coal. After the fracturing fluid invades, the desorption hysteresis of methane and CO2 in coal was found to be amplified. The impact on the methane desorption hysteresis is significantly higher than CO2 does. The reason for the increasing of hysteresis may be that the adsorption swelling caused by the residue adhered on the pore edge, or the pore blockage caused by the residue invasion under high gas pressure. The results of this study quantitatively confirm the fracturing fluid induced gas sorption damage on coal and provide a baseline assessment for coal fracturing fluid formulation and technology.

Effect of Acidizing Process on the Stress Corrosion Cracking of HP-13Cr Stainless Steel in the Ultra-depth Well Environment

The effect of acidizing process on the stress corrosion cracking of HP-13Cr stainless steel in the ultra-depth well environment was studied by the slow strain rate test, the electrochemical measurement, the microstructure observation, and the finite element modeling. The results indicated that the acidizing process significantly increased the stress corrosion cracking susceptibility of HP-13Cr stainless steel and induced the fracture mode to the brittle characteristic in the high temperature and CO2 pressure environment. The stress corrosion cracking susceptibility also increased with the increase of temperature and CO2 pressure. There were dense defects including pits and cracks in the fracture section from the transverse view. After the acidizing process, under tensile stress condition, the increasing roughness will cause the stress concentration and promote the local anodic dissolution, which induces the initiation of stress corrosion cracking.

Experimental Study of Prefabricated Crack Propagation in Coal Briquettes under the Action of a CO2 Gas Explosion.

CO2 deep-hole presplit explosions are an important technology for enhancing gas drainage in low-permeability coal seams. In the process of a CO2 gas explosion, the initial burst crack generated by the shock wave expands the crack tip under the splitting action of high-pressure CO2 gas. To explore the effects of CO2 gas explosions on crack tips, we constructed an analytical model of gas pressure attenuation at different positions based on fluid motion equations, proposed equations for crack opening and growth rates, and inverted the energy field of the whole process of CO2 blasting. We used a test platform for the independent development of CO2 gas explosions under experimental conditions of 1 MPa axial pressure and 2 MPa CO2 gas pressure and a VIC-3D measurement system. We conducted the gas explosion experiments on prefabricated cracked samples with a crack length of 10 mm and width of 0.2 mm to analyze the dynamic response of the crack tip. The results showed that there were three stages in the propagation of a prefabricated crack under the action of a CO2 gas explosion. The first stage, from 0 to 290 ms, included energy storage at the crack tip and a maximum opening rate increment of 0.0043 m/s. The second stage, from 291 to 295 ms, was rapid crack propagation with maximum opening rate increment and propagation rates of 0.1865 and 5.35 m/s, respectively. In the third stage, from 296 to 309 ms, the crack tip propagated slowly, the maximum opening rate increment and growth rates were 0.0969 and 5.81 m/s, respectively, and the crack arrest coordinates were 4.57 and 35.28 mm. The experimental study verified the accuracy of the calculation model, proved that CO2 gas promotes the growth of crack tips, explained the spatiotemporal evolution mechanism of the CO2 explosion process, and provided experimental support for subsequent research related to explosions.