Gas breakthrough experiments on pelitic rocks: comparative study with N2, CO2 and CH4

The capillary‐sealing efficiency of intermediate‐ to low‐permeable sedimentary rocks has been investigated by N₂, CO₂ and CH₄ breakthrough experiments on initially fully water‐saturated rocks of different lithological compositions. Differential gas pressures up to 20 MPa were imposed across samples of 10–20 mm thickness, and the decline of the differential pressures was monitored over time. Absolute (single‐phase) permeability coefficients (k_abs), determined by steady‐state fluid flow tests, ranged between 10^?22 and 10^?15 m². Maximum effective permeabilities to the gas phase k_eff(max), measured after gas breakthrough at maximum gas saturation, extended from 10^?26 to 10^?18 m². Because of re‐imbibition of water into the interconnected gas‐conducting pore system, the effective permeability to the gas phase decreases with decreasing differential (capillary) pressure. At the end of the breakthrough experiments, a residual pressure difference persists, indicating the shut‐off of the gas‐conducting pore system. These pressures, referred to as the ‘minimum capillary displacement pressures’ (P_d), ranged from 0.1 up to 6.7 MPa. Correlations were established between (i) absolute and effective permeability coefficients and (ii) effective or absolute permeability and capillary displacement pressure. Results indicate systematic differences in gas breakthrough behaviour of N₂, CO₂ and CH₄, reflecting differences in wettability and interfacial tension. Additionally, a simple dynamic model for gas leakage through a capillary seal is presented, taking into account the variation of effective permeability as a function of buoyancy pressure exerted by a gas column underneath the seal.     

Meteorological influences on the spatial and temporal variability of NO2 in Toronto and Hamilton

The spatial and temporal variability of nitrogen dioxide (NO₂) concentrations and their relationships with meteorology was evaluated in the Toronto–Hamilton urban airshed. NO₂ concentrations were highest in the early morning and late evening. Mean concentrations were highest in winter, although individual one-hour NO₂ concentrations were found to be highest in summer. Wind direction was the strongest control on hourly NO₂ concentration, and temperature and wind speed also had an effect. Our analysis of NO₂ concentration variation by wind direction showed that areas downwind of major highways, urban centres and industry were exposed to higher pollutant concentrations. Seasonal patterns of NO₂ concentration displayed significant spatial heterogeneity, in particular, in Toronto. Onshore winds sheltered coastal inhabitants from the full extent of NO₂ exposure they would otherwise experience. Seasonal variations in meteorology and emissions mean that the degree of spatial variability in NO₂ concentrations changes from season to season. This study will help to improve existing land-use regression-based NO₂ prediction models by incorporating meteorological controls on NO₂ distributions for health effect studies.     

Gas breakthrough pressure for hydrocarbon reservoir seal rocks: implications for the security of long-term CO2 storage in the Weyburn field

This paper reports a laboratory study of the gas breakthrough pressure for different gas/liquid systems in the Mississippian‐age Midale Evaporite. This low‐permeability rock formation is the seal rock for the Weyburn Field in southeastern Saskatchewan, Canada, where CO₂ is being injected into an oil reservoir for enhanced recovery and CO₂ storage. A technique for experimentally determining CO₂ breakthrough pressure at reservoir conditions is presented. Breakthrough pressures for N₂, CO₂ and CH₄ were measured with the selected seal‐rock samples. The maximum breakthrough pressure is over 30 MPa for N₂ and approximately 21 MPa for CO₂. The experimental results demonstrate that the Weyburn Midale Evaporite seal rock is of high sealing quality. Therefore, the Weyburn reservoir and Midale Beds can be used as a CO₂ storage site after abandonment. The measured results also show that the breakthrough pressure of a seal rock for a gas is nearly proportional to the interfacial tension of the gas/brine system. The breakthrough pressure of a CO₂/brine system is significantly reduced compared with that of a CH₄/brine system because of the much lower interfacial tension of the former. This implies that a seal rock that seals the original gas in a gas reservoir or an oil reservoir with a gas cap may not be tight enough to seal the injected CO₂ if the pressure during or after CO₂ injection is the same or higher than the original reservoir pressure. Therefore, reevaluation of the breakthrough pressure of seal rocks for a given reservoir is necessary and of highest priority once it is chosen as a CO₂ storage site.     

Hydrogeochemical modelling of CO2 equilibria and mass transfer induced by organic–inorganic interactions in siliciclastic petroleum reservoirs

Different feldspar types control complex hydrogeochemical processes in hydrocarbon‐bearing siliciclastic reservoirs, which have undergone different degrees of degradation. To test such processes generically, carbon dioxide equilibria and mass transfers induced by organic–inorganic interactions have been modelled for different hydrogeochemical scenarios. The approach is based on and compared with data from the Norwegian continental shelf ( Smith & Ehrenberg 1989 ) and assumes local thermodynamic equilibrium among solids and fluids. Equilibrating mineral assemblages (different feldspar types, quartz, kaolinite, calcite) are based on the primary reservoir composition. Equilibration and coupled mass transfer were triggered by the addition and reaction of different amounts of CO₂, CH₄ and H₂ (plus acetic acid) at temperatures between 50 and 95°C (323 and 368 K). These components occur in oil fields as products of anaerobic bacterial degradation, hydrolytic disproportionation of hydrocarbons and/or thermal maturation of kerogen. We apply two different computer codes and two different thermodynamic data bases to calculate the results. Reaction of 0.32–0.6 mol CO₂, 0.16–0.3 mol CH₄ and 0.8–1.5 mol H₂ with K‐feldspar, quartz, kaolinite and calcite in 1 l of pore water results in modelled values of 0.3–2.3 mol% CO₂ in a multicomponent gas phase that resembles measured data (0.2–1.5 mol%). Similar CO₂ contents result from acetic acid addition (CO₂, CH₄, H₂ + 0.016 mol CH₃COOH). Equilibration with albite or anorthite reduces the release of CO₂ into the multicomponent gas phase dramatically, by 1 or 4 orders of magnitude compared with the equilibration with K‐feldspar. Minor differences in the modelled CO₂ content (0.1–0.2 mol%) result from calculations with different computer codes if the same thermodynamic data base is applied. Relevant differences (up to 1.9 mol% CO₂) result from calculations using different thermodynamic data bases.     

Conceptualizing and Researching Policy Convergence1

This article develops criteria to classify the relative development of public policies across countries as convergent, divergent, identical and synchronous, and indeterminate. It emphasizes that relative policy developments have to be compared over defined time periods, and that they cannot be aggregated or averaged over several time periods, or across policy sectors or policy dimensions. The significance of policy convergence between countries needs to be evaluated against relative policy developments between other countries during the same period. Given these rigorous conceptual and methodological requirements, it is doubtful whether policy convergence is as pervasive as generally assumed in the literature.     

超临界CO2流体干燥海洋出水木质文物的实验研究

有研究表明,相较于传统的干燥技术,利用超临界CO₂流体干燥技术对出土饱水竹木器进行干燥具有周期短、变形小的优势。与出土饱水竹木器相比,海洋出水木质文物除了含水率高外,还含有较多的难溶性盐分,在文物的长期保存和展览中,盐分与水分、空气、文物本身进行化学反应会加速文物的老化和腐蚀。因此,本研究以“南海Ⅰ号”船体的部分构件为研究对象,开展了将超临界CO₂流体干燥技术应用于海洋出水木质文物的探索实验研究。实验结果表明,在温度40 ℃,压力20 MPa的条件下,超临界CO₂流体干燥海洋出水木质文物效果明显,样品的三向干缩率均低于或者接近健康木材阴干的三向干缩率;含水率大幅度下降,经过超临界技术干燥后不需再做其他干燥处理就能满足文物保存的要求。文物干燥前后含盐率的测量结果表明,此干燥技术还具有明显脱盐的效果。     

The Northern Ireland Conflict: A Framework for Discussion1

At the Dublin Antipode Conference of March 1978, a debate occurred on the Northern Ireland question. In what follows we present extended versions of two of the papers (those by Boal and Anderson). We have also included other pertinent material in the form of Pringle's essay and Perron's review. Hopefully both of these papers will add a further dimension to the debate. In the case of Anderson's paper, due to both time and space limitations, the editorial collective reduced his original work substantially.     

可溶盐NaCl和CaCl2对陶质文物的酥粉作用

研究可溶盐NaCl和CaCl_2复合盐破坏陶质文物过程中作用本质,在复合盐溶液的平衡结晶相分析基础上,分析陶质样品中可溶盐溶液的吸收和水分蒸发速率变化,以及采用超景深显微系统、扫描电子显微系统等检测可溶盐NaCl、CaCl_2和复合盐溶液对陶质样品的破坏过程和作用。结果表明:陶质样品破坏的本质在于可溶盐结晶受力过程中微裂纹的扩展和贯通,在环境相对湿度变化引起裂纹扩展贯通过程中,陶质样品表面逐层粉化脱落,质量、形貌和强度都发生着一定程度的改变,其中NaCl结晶体对陶质样品产生的作用力较大,破坏性最强,而NaCl溶液中加入的CaCl_2延长了盐结晶所需要的时间,间接地阻碍了NaCl的结晶析出,反而对陶质样品起到了一定的保护作用。研究结果为进一步酥粉陶质文物的保护研究提供科学依据。     

陕西境内遗址表面CaSO42H2O产生之水盐运移规律研究

陕西境内遗址出土后短时间内表面产生白色物质CaSO₄2H₂O是非常普遍的现象。本研究利用土柱模拟遗址出土后表面产生CaSO₄2H₂O的过程,通过监测土柱中土壤的湿度、含盐量及离子变化综合分析CaSO₄2H₂O产生的原因,研究结果表明遗址出土后形成了新的界面层,在蒸发的作用下,地下水沿土壤孔隙向上迁移,同时将可溶盐带入土壤中,表面的可溶盐含量逐渐增大,达到峰值后不再增加,实验后测得表面土壤中的Ca²⁺和SO2-₄是原始土壤的数十倍,说明遗址表面产生CaSO₄2H₂O是水盐运移的结果。本研究可为遗址出土后预防CaSO₄2H₂O的产生提供依据。     

SO2与水分综合影响下的云冈石窟砂岩劣化研究

气体污染物SO₂是造成云冈石窟文物本体劣化的重要因素之一。为厘清SO₂与水分耦合作用下的云冈砂岩劣化规律，开展不同SO₂浓度、相对湿度以及降水条件下的室内模拟风化试验，测定试样质量、表面特征和化学成分变化。结果表明：SO₂易与砂岩中的碳酸盐矿物(如方解石)和长石发生化学反应，产物包括CaSO₄·2H₂O、MgSO₄·7H₂O和高岭石等，且随着相对湿度增加，反应程度增大，造成试样的质量、色差值、可溶盐含量上升及硅铝比下降；液态水的参与能显著加快SO₂与砂岩的相互作用过程，不但增加了各项指标的变化幅度，还加大了SO₂入侵深度。研究成果可为砂岩质文物的科学认知和预防性保护提供参考。     

海底打捞铁质文物的腐蚀机理及其脱氯方法

综述了铁质文物在海水中及打捞出水后的腐蚀机理,如电化学循环机理、氧浓差电池腐蚀机理等,同时简述了从海水中打捞出来的铁质文物的各种脱氯方法,包括碱性溶液浸泡法、碱性亚硫酸盐还原法,电解还原法及高温还原法等.     

International Assistance to the Former Soviet Union: Conditions and Transitions1

Since the demise of the Soviet Union the newly independent states (NIS) have attempted the wholesale reform of their economic, political, and social institutions. With varying levels of success they have sought to create new institutions or reorganize old institutions, often so as to mirror similar institutions in western Europe and North America. Many nations and international organizations have sought to influence these transitions with technical assistance, foreign aid, concessional loans, and trade/investment promotion programs. In this article we attempt to bridge the conceptual, analytic, and empirical gaps between those who argue that external influences remain unimportant and those who believe that international organizations and foreign governments can support reforms. Specifically, we argue that although external assistance can play a positive role in the successful consolidation of political and economic reforms, the contribution of external assistance to the post-Soviet transitions has been limited by the institutional arrangements, technical proficiency, and political motivations of the aid providers. We thus analyze patterns of foreign assistance to demonstrate that implicit conditionalities imposed by aid donors upon recipient countries—with regard to geographic distribution, program priorities, timing, and graduation criteria—often force recipients to comply with reform agendas that may or may not be favorable for the recipient.