Flue gas and pure CO2 sorption properties of coal: A comparative study

Presently many research projects focus on the reduction of anthropogenic CO₂ emissions. It is intended to apply underground storage techniques such as flue gas injection in unminable coal seams. In this context, an experimental study has been performed on the adsorption of pure CO₂ and preferential sorption behavior of flue gas. A coal sample from the Silesian Basin in Poland (0.68% V Rr), measured in the dry and wet state at 353 K has been chosen for this approach. The flue gas used was a custom class industrial flue gas with 10.9% of CO₂, 0.01% of CO, 9% of H₂, 3.01% of CH₄, 3.0% of O₂, 0.106% of SO₂ and nitrogen as balance.Adsorption isotherms of CO₂ and flue gas were measured upto a maximum of 11 MPa using a volumetric method. Total excess sorption capacities for CO₂ on dry and wet Silesia coal ranged between 1.9 and 1.3 mmol/g, respectively. Flue gas sorption capacities on dry and wet Silesia coal were much lower and ranged between 0.45 and 0.2 mmol/g, respectively, at pressures of 8 MPa. The low sorption capacity of wet coal has resulted from water occupying some of the more active adsorption sites and hence reducing the heterogeneity of adsorption sites relative to that of dry coal. Desorption tests with flue gas were conducted to study the degree of preferential sorption of the individual components. These experiments indicate that CO₂ is by far the prefered sorbing component under both wet and dry conditions. This is followed by CH₄. N₂ adsorbs very little on the coal in the presence of CO₂ and CH₄. It is also observed that the adsorption of CO₂ onto coal is not significantly hindered by the addition of other gases, other than dilution effect of the pressure.In addition to the sorption experiments, the density of the flue gas mixture has been determined up to 18 MPa at 318 K. A very good precision of these measurements were documented by volumetric methods.     

Selection of coals of different maturities for CO2 Storage by modelling of CH4 and CO2 adsorption isotherms

CO₂ injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO₂ and CH₄) for well-characterised coals of different maturities to determine the most suitable coal for CO₂ storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO₂ and CH₄ pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO₂ adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO₂ storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO₂ adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO₂ storage capacities. Our study provides high quality affinity parameters and values of CO₂ and CH₄ adsorption capacities on various coals for the future modelling of CO₂ injection in coal seams.     

Predicted CO2 emissions from maceral concentrates of high volatile bituminous Kentucky and Illinois coals

A large collection of well-characterized coals, documented in the Center for Applied Energy Research's (CAER) database, was used to estimate the CO₂ content of maceral concentrates from Kentucky and Illinois high volatile bituminous coals. The data showed no correlation between CO₂ versus coal ranks and between CO₂ versus maceral content. Subsequently, eight sets of low-ash density-gradient centrifugation (DGC) maceral concentrates from five coal beds were examined, spanning in the high volatile rank range. Heating value was not determined on the concentrates, but instead was calculated using the Mott–Spooner formula. There was a good correlation between predicted CO₂ and maceral content for the individual iso-rank (based on vitrinite reflectance, analyzed on whole (parent) coal) sets. In general, the predicted CO₂ increases from liptinite-rich through vitrinite-rich to inertinite-rich concentrates (note: no “concentrates” are absolutely monomaceral).     

The rise of trees and their effects on Paleozoic atmospheric CO2 and O2

The rise of large vascular plants during the mid-Paleozoic brought about a major increase in the rates of weathering of silicate minerals that induced a drop in the level of atmospheric CO₂ and contributed, via the atmospheric greenhouse effect, to global cooling and the initiation of the most long lived and a really extensive glaciation of the past 550 million years. Sedimentary burial of the microbiologically resistant remains of the plants resulted during the Permo-Carboniferous in both further lowering of CO₂ and in elevation of atmospheric O₂. Evidence of changes in CO₂ and O₂ are provided by mathematical models, studies of paleosols, fossil plants, fossil insects, and the effects of modern plants on silicate weathering, and by laboratory studies of the effects of changes in O₂ on plants and insects. To cite this article: R.A. Berner, C. R. Geoscience 335 (2003).     

Geologic factors controlling CO2 storage capacity and permanence: case studies based on experience with heterogeneity in oil and gas reservoirs applied to CO2 storage

A variety of structural and stratigraphic factors control geological heterogeneity, inferred to influence both sequestration capacity and effectiveness, as well as seal capacity. Structural heterogeneity factors include faults, folds, and fracture intensity. Stratigraphic heterogeneity is primarily controlled by the geometry of depositional facies and sandbody continuity, which controls permeability structure. The permeability structure, in turn, has implications for CO₂ injectivity and near-term migration pathways, whereas the long-term sequestration capacity can be inferred from the production history. Examples of Gulf Coast oil and gas reservoirs with differing styles of stratigraphic heterogeneity demonstrate the impact of facies variability on fluid flow and CO₂ sequestration potential. Beach and barrier-island deposits in West Ranch field in southeast Texas are homogeneous and continuous. In contrast, Seeligson and Stratton fields in south Texas, examples of major heterogeneity in fluvial systems, are composed of discontinuous, channel-fill sandstones confined to narrow, sinuous belts. These heterogeneous deposits contain limited compartments for potential CO₂ storage, although CO₂ sequestration effectiveness may be enhanced by the high number of intraformational shale beds. These field examples demonstrate that areas for CO₂ storage can be optimized by assessing sites for enhanced oil and gas recovery in mature hydrocarbon provinces.     

四川盆地理论CO_2地质利用与封存潜力评估

结合CO_2地质利用与封存技术机理,在国际权威潜力评估公式的基础上,系统地提出了适合中国地质背景的次盆地尺度CO_2封存潜力评估方法及关键参数取值。同时,以四川盆地为例,依次开展了枯竭油田地质封存与CO_2强化石油开采、枯竭气田与CO_2强化采气、不可采煤层地质封存与CO_2驱替煤层气,以及咸水层地质封存技术的CO_2地质封存潜力。结果表明,四川盆地利用深部咸水层与枯竭天然气田CO_2地质封存潜力最大,期望值分别达154.20×10~8t和53.73×10~8t。其中,枯竭天然气田因成藏条件好、勘探程度高、基础建设完善,为四川盆地及其周边利用枯竭气田CO_2地质封存技术实现低碳减排提供了早期示范机会。CO_2地质利用与封存潜力评估方法,对进一步开展全国次盆地尺度理论封存潜力评估与工程规划具有重要意义。     

二氧化碳羽流地热系统的碳封存经济分析

【研究目的】 二氧化碳羽流地热系统（CPGS）在取热的同时可实现CO₂地质封存，在碳达峰与碳中和背景下，CPGS碳封存的经济性是众多学者关注的要点。【研究方法】 以松辽盆地泉头组为例，采用数值模拟方法对比分析了注入压力、井间距与回注温度对热提取率的影响，在供暖情景下，计算了CPGS供暖效益与碳封存成本，并与常规水热型地热系统供暖效益进行了对比。【研究结果】 受携热介质转变与热突破影响，CPGS开采井温度呈现“降低-稳定-降低”的趋势，其中井间距对开采井温降影响显著，井间距越小开采井温降越明显；热提取率与回注压力呈现正相关性，与回注温度呈现负相关性，井间距对热提取率影响不显著；CPGS与常规水热型地热系统相比，采热量呈现“高-低-高”三个阶段，其中回注压力越小、回注温度与储层温度越接近，实现CPGS较水介质多采热能所需的时间越短。【结论】 仅考虑CO₂价格与取热效益，供暖收益抵消部分碳封存成本后，井间距对CO₂封存单位成本影响最为显著，井间距越小，CO₂封存单位成本降低越迅速，在注采井间距300 m条件下，持续开采30 a后CO₂封存单位成本可降至160元/t。     

Laboratory study of self-potential signals during releasing of CO2 and N2 plumes

Carbon Capture Sequestration (CCS) projects require, for safety reasons, monitoring programmes focused on surveying gas leakage on the surface. Generally, these programmes include detection of chemical tracers that, once on the surface, could be associated with CO₂ degassing. We take a different approach by analysing feasibility of applying electrical surface techniques, specifically Self-Potential. A laboratory-scale model, using water-sand, was built for simulating a leakage scenario being monitored with non-polarisable electrodes. Electrical potentials were measured before, during and after gas injection (CO₂ and N₂) to determine if gas leakage is detectable. Variations of settings were done for assessing how the electrical potentials changed according to size of electrodes, distance from electrodes to the gas source, and type of gas. Results indicated that a degassing event is indeed detectable on electrodes located above injection source. Although the amount of gas could not be quantified from signals, injection timespan and increasing of injection rate were identified. Even though conditions of experiments were highly controlled contrasting to those usually found at field scale, we project that Self-Potential is a promising tool for detecting CO₂ leakage if electrodes are properly placed.     

水射流破碎联合CO2置换开采天然气水合物新工艺及实验研究

本文对目前开采天然气水合物的5种方法进行了归纳总结,重点分析了CO₂置换开采以及固体开采法,并通过分析这2种开采方法的优劣势,提出了水射流冲蚀、破碎海洋天然气水合物储层联合CO₂置换开采天然气水合物的新思路。水射流冲蚀、破坏水合物储层后形成的采空区能为CO₂提供更好的储藏空间并提高其与储层的作用面积,提高置换效率;封存的CO₂水合物也可以提高水合物储层的稳定性,具有良好的互补效应。实验结果表明,在整个置换过程中,含采空区储层CH₄置换率为24.3%,CO₂封存率为22.1%;完整储层CH₄置换率为15.3%,CO₂封存率为20.9%,置换率提升约59%,封存率提升约5.7%。采空区的作用主要体现在提升水合物置换介质的注入量上。     

全国二氧化碳地质储存适宜性评价编图技术方法研究

将全国CO2地质储存潜力与适宜性评价工作划分为5个阶段,依次为区域级预测潜力(E级)评价、盆地级推定潜力(D级)评价、目标区级控制潜力(C级)评价、场地级基础储存量(B级)评价和灌注级工程储存量(A级)评价阶段.第一阶段编制的成果图件主要为全国1∶500万CO2地质储存成果图系;第二、三阶段主要编制沉积盆地CO2地质储存成果图集;第四、五阶段主要编制CO2地质储存示范工程成果图册.提出中国CO2地质储存潜力与适宜性评价和编图是一项有步骤、分阶段逐步完成的工程,评价及编图方法有待通过潜力与适宜性评价和编图的实践不断完善.     

黑钨矿有效沉淀机制:CO2逃逸

黑钨矿是石英脉钨矿床的主要矿石矿物,其沉淀机制一直存在争议。CO₂逃逸能否造成黑钨矿有效沉淀尚缺乏定量模型的评价。文章建立了W-Fe-Cl-Na-O-C-H体系的反应平衡模型,涉及22种组分和16个化学反应;相关热力学参数来自SUPCRT数据库。模型计算结果表明,pH与流体压力呈负相关关系,而钨溶解度与流体压力呈正相关关系;当成矿流体压力从静岩压力降至静水压力水平,钨溶解度降幅可达到27%~47%,降幅与温度和深度成正比。因而,降压造成的CO₂逃逸是黑钨矿沉淀的有效机制之一。      

采空区对CO2置换开采海域天然气水合物置换效果影响的实验研究

为揭示固体开采形成的采空区对CO₂置换开采天然气水合物置换效果的影响,开展了含采空区储层与完整储层的CO₂/N₂置换开采不同天然气水合物饱和度对比实验研究。结果表明：对于水合物饱和度分别为30%和45%的试样,含采空区储层较完整储层的CH₄置换率分别提高了5.5%和9%,单位体积CO₂封存量分别提高了26.5%和39.8%。采空区的存在提高了置换介质与天然气水合物的摩尔比率,从而提供了更高的置换驱动力;且在较高水合物饱和度试样中采空区还会提高置换介质的扩散作用,导致含采空区储层的置换效果好于完整储层。因此,在固体开采后进一步进行CO₂置换开采,可以提高置换开采效率,同时有助于碳封存与地层稳定,是一种潜在的海域天然气水合物安全、绿色开采模式。     

温室气体CO2与钠长石相互作用实验研究

为寻求减缓全球变暖的途径,利用高压釜,开展不同温度下(75、100、125、150和175℃)CO₂与钠长石的水热实验研究,以探讨CO₂在长石砂岩中地质封存的可能性。结果表明,随着温度的升高,钠长石溶蚀强度逐渐增强,在150℃左右开始有菱镁矿、菱铁矿等碳酸盐矿物生成,175℃新矿物生成量增加,这表明CO₂能够以碳酸盐矿物的形式在含钠长石的长石砂岩中以矿物的形式被“固定”,其被“固定”的温度在150℃左右。     

中国二氧化碳地质储存潜力评价与示范工程

2010—2012年,中国地质调查局水文地质环境地质调查中心承担完成的“全国二氧化碳地质储存潜力评价与示范工程计划项目”,全面建立了我国二氧化碳地质储存潜力与适宜性评价指标体系与评价技术方法,评价了主要沉积盆地的二氧化碳地质储存潜力与适宜性,完成了全国1∶500万评价图系和主要盆地评价图集编制,圈定出一批二氧化碳地质储存目标靶区;构建了深部咸水层二氧化碳地质储存工程选址、场地勘查与评价技术方法;与神华集团合作,在内蒙古鄂尔多斯市伊金霍洛旗成功实施了我国首个深部咸水层二氧化碳地质储存示范工程,基本形成了我国二氧化碳地质储存基本理论和技术方法体系。     

Experimental identification of CO2–water–rock interactions caused by sequestration of CO2 in Westphalian and Buntsandstein sandstones of the Campine Basin (NE-Belgium)

Geological sequestration of CO₂ is one of the options studied to reduce greenhouse gas emissions. Although the feasibility of this concept is proven, apart from literature data on modelling still little is known about the CO₂–water–rock interactions induced by CO₂-injection.To evaluate the effect of CO₂–water–rock interactions on three sandstone aquifers in NE-Belgium an experimental setup was built. Eighteen experiments were performed in which sandstones were exposed to supercritical CO₂. CO₂–water–rock interactions were deduced from the evolution of aqueous concentrations of 25 species and a thorough characterisation of the sandstones before and after treatment. The results show that dissolution of ankerite/dolomite and Al-silicates could enhance porosity/permeability. The observed precipitation of end-member carbonates could increase storage capacity if it exceeds carbonate dissolution. Precipitation of the latter and of K-rich clays as observed, however, can hamper the injection.     

Methane and carbon dioxide adsorption–diffusion experiments on coal: upscaling and modeling

Numerical modelling of the processes of CO₂ storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO₂ and CH₄ were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VR_r=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to 3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO₂ sorption was consistently faster than CH₄ sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO₂ and CH₄ that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO₂ and CH₄ can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.     

汶川M_s 8.0地震破裂带CO_2、CH_4、Rn和Hg脱气强度

地震活动断裂带能够向大气释放大量的温室气体、放射性气体和有毒气体(CO_2、CH_4、Rn和Hg),并对大气环境的影响产生复杂的影响。利用静态暗箱法,对汶川M_s8.0地震破裂带CO_2、Rn和Hg脱气强度进行实地测量,并计算了CO_2和Hg脱气对大气的年贡献量。结果表明:(1)破裂带土壤气中CO_2、CH_4、Rn和Hg异常浓度最大值分别可以达到7.98%、2.38%、524.30k Bq/m~3和161.00ng/m~3;破裂带CO_2、Rn和Hg脱气平均通量是34.95g·m~(-2)d~(-1)、36.11m Bq·m~(-2)s~(-1)和26.56ng·m~(-2)h~(-1),最大值分别达到259.23g·m~(-2)d~(-1)、580.35m Bq·m~(-2)s~(-1)和387.67ng·m~(-2)h~(-1);(2)汶川Ms8.0地震破裂带向大气脱气的CO_2年贡献量是0.95Mt,Hg的年贡献量是15.94kg。汶川Ms8.0地震破裂带破裂CO_2、CH_4、Rn和Hg等的脱气强度,不仅与破裂带渗透率有关,还与断裂带浅部存在的气藏、煤层以及磷矿层等气体源有重要的联系。     

松辽盆地含CO_2火山岩气藏的形成和分布

松辽盆地特有的深部构造背景和裂谷演化特征,造成盆地内含CO_2火山岩气藏的形成和富集。松辽裂谷盆地中新生代火山岩浆活动发育,总体上具有多期喷发、分布广泛和储集条件良好的特点。火山活动以中心式喷发为主,主要发育中基性-酸性火山岩,发育流纹岩、凝灰岩等多种岩石类型,爆发相和溢流相2种火山岩相。中生代火山岩在盆地内分布广泛,营域组构成深层有利储层,新生代火山岩在盆地外围出露较多,而在盆内出露较少。盆地高含量的二氧化碳为无机幔源成因,由青山口期和新生代幔源岩浆脱气形成。含CO_2火山岩气藏的形成主要受深部构造背景、深大断裂和中新生代火山岩控制。已发现含CO_2火山岩气藏主要分布于古中央隆起带及其两侧断陷的营城组火山岩中,具有点状、带状分布,局部富集的特点。根据主控因素分析,预测了5个CO_2富集区带。     

CO2气综合识别技术及应用

CO₂气藏由于其物理、化学性质的特殊性,CO₂气勘探与烃类气既有相同又有区别,综合应用多种资料和多种技术方法是识别CO₂气(层)藏的有效手段。利用区域地质分析、地球物理和地球化学勘探方法综合评价非烃气的分布,提出钻探目标,通过非烃色谱测量法和红外线CO₂气体浓度测量法实现CO₂气层钻井现场动态检测,利用气体色谱检测相关录井参数资料、核测井密度中子孔隙度差值综合解释CO₂气层,有效地识别CO₂气。主要介绍CO₂气藏综合勘探技术的关键的新技术方法,如地球化学方法、录井和测井综合识别的关键技术方法等。     

CO2流体对火山碎屑岩改造作用的实验研究

以塔木察格盆地火山碎屑岩为研究对象,研究不同温度下(100、120、140、160、180℃)CO2流体对火山碎屑岩(流纹质凝灰岩、沉凝灰岩)成分的改造.研究发现:在CO2流体的作用下,火山碎屑岩中的长石、碳酸盐矿物发生溶蚀,且其溶蚀强度随温度的升高而增大,石英的溶蚀程度较弱;火山碎屑岩中的凝灰质成分易溶蚀,并且是CO2流体溶蚀火山碎屑岩的主要对象;通过扫描电镜观察发现沉凝灰岩在160℃下样品表面有绿泥石(?)和一水软铝石(?)生成.结合塔木察格盆地中的碳酸盐矿物(尤其是片钠铝石)的存在及盆地中次生溶孔大量发育的特征,认为盆地内有CO2流体活动且CO2流体对塔木察格盆地次生孔隙的形成有重要的贡献.