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- Carvões portugueses: A revalorização moderna possível de um recurso geológico. O caso-de-estudo da Bacia Carbonífera do DouroPublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Diogo, Miguel Tato; Pinto de Jesus, A.; Mouraz Miranda, A.; Dinis, Maria Alzira Pimenta; Oliveira, Gisela; Chaminé, H.I.; Dinis da Gama, C.; Arrais, C.M.Na sequência de uma síntese sobre as formações datadas do Carbonífero presentes na Bacia Carbonífera do Douro e seu enquadramento geológico, os autores descrevem os estudos modernos, nomeadamente no domínio da estratigrafia efectuados na bacia. Após o fecho das minas de metantracites da bacia (1972 na área do Couto Mineiro de São Pedro da Cova e 1994 na área do Couto Mineiro do Pejão) desenvolveram-se outros importantes estudos, designadamente na área do Couto Mineiro do Pejão, relacionados com o fim da actividade mineira, nomeadamente nos domínios de subsidência mineira e afluxos de água e seus aspectos geológicos e hidrogeomecânicos, estudos estes de que se dá igualmente relato no presente trabalho. Por fim, apresenta-se o essencial do Projecto-Piloto COSEQ elaborado com vista a definir a possível revalorização, em termos modernos, das metantracites da Bacia Carbonífera do Douro como potencial meio de sequestração geológica de CO2. Com efeito, os carvões durienses constituem, hoje, um recurso geológico abandonado do ponto de vista mineiro tradicional.
- Workshop on "Energy, greenhouse gases and environment" proceedings, presentations and postersPublication . Lemos de Sousa, M. J.; Oliveira, Gisela; Rodrigues, Cristina; Dinis, Maria Alzira Pimenta; Diogo, Miguel Tato; Barros, Nelson
- O Carvão na ActualidadePublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Dinis, Maria Alzira Pimenta
- Effect of gas compressibility factor estimation in coal sorption isotherms accuracyPublication . Rodrigues, Cristina; da Silva, J.M. Machado; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.Compressibility factor (CF) is a key parameter in gas industry, regarding gas flow and storage in a gas reservoir. This study highlights the necessity to accurately estimate CF, affecting reservoir sorption capacity determination. The effect of the CF of N2, CH4 and CO2 in the coal porous structure was studied. Sorption isotherms showed no significant hysteresis regarding N2, due to gas inert behaviour. CH4 has a higher CF slope and the hysteresis behaviour is stronger than in N2. CO2 has no linear CF behaviour and besides relevant hysteresis, a distinct general trend between both curve shapes was identified, and the CO2 desorption curve intercepted the CO2 adsorption curve at 30x105 Pa. This is due to CO2 retention on coal porous structure, thanks to the great affinity between CO2 and the organic microporous structure, to pressures up to 6.9x105 Pa. The gas mixture showed a significant hysteresis due to its composition.
- Comparative study of the influence of minerals in gas sorption isotherms of three coals of similar rankPublication . Rodrigues, Cristina; Pinheiro, H. J.; Lemos de Sousa, M. J.; yesThis investigation compares the gas adsorption behaviour and capacity of three bituminous coals from South Africa, of similar rank, by assessing the characteristics of the raw coal, as well as the resulting float and sink fractions (at 1.80 cm3/g) obtained by density separation of crushed coal samples. Calculations were also made to obtain the raw coal gas storage capacity from the weighted contribution of both float and sink fractions results, thereby permitting comparison with the analysed results of the raw coal. The study demonstrated that the clean fraction of a coal has the highest capacity to retain gas in the sorbed state, followed by raw coal, and lastly the sink fraction, and re–confirmed previous investigations that showed minerals to be inhibitors of gas adsorption and retention.
- Sequestração geológica de dióxido de carbono: notas sobre o estado-da-artePublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Oliveira, GiselaApós uma breve introdução sobre os conceitos de (i) Alterações climáticas vs Alterações globais e de (ii) Gases de efeito de estufa, os autores apresentam o estado-da-arte sobre os principais problemas relacionados com a redução do dióxido de carbono e sua sequestração geológica. Por fim, fazem referência aos projectos existentes neste domínio no “Grupo de Investigação em Energia” do Centro de Investigação em Alterações Globais, Energia, Ambiente e Bioengenharia - CIAGEB da Universidade Fernando Pessoa. After a short introduction regarding concepts such as (i) Climate change vs Global changes, and (ii) Greenhouse gases effect, the authors present the state-of-the-art regarding problems related with Carbon dioxide abatement and geological sequestration. Finally, the authors refer to the current projects on this particular issue being developed by the “Energy Research Group” of the Global Change, Energy, Environment and Bioengineering RDID&D Unit – CIAGEB of Universidade Fernando Pessoa.
- Gas diffusion coefficient in coal: calculation of tangent slope accuracy through the inflection point determinationPublication . Rodrigues, Cristina; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.This investigation aims to develop an accurate method to calculate the tangent slope (b) - a fundamental parameter to calculate gas diffusion coefficients under different pressures - using inflection point determinations. The authors also studied the different tangent slope behaviours depending on the experimental gas sorption used. The single Langmuir model, for individual gases, and the extended Langmuir model, for multicomponent gas mixtures, were applied to fit experimental gas sorption isotherm data. Two coals were selected in order to minimize and/or avoid the maceral composition and vitrinite mean random reflectance effects. Samples were submitted to three different gas compositions, viz. 99.999% CH4; 99.999% CO2; and a gas mixture containing 74.99% CH4 + 19.99% CO2 + 5.02% N2. Results showed that the first and the second derivatives calculated to define the first inflection points represent exactly the final limit of tangent slopes.
- Gas content derivative data versus diffusion coefficientPublication . Rodrigues, Cristina; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.The study of the gas diffusion process has a main role in both Coalbed Methane (CBM) production and CO2 injection in geological sequestration projects. The accurate determination of gas diffusion coefficients in unconventional reservoirs such as coal seams, requires a consistent mathematical approach. The study of the gas diffusion process in coal seams was carried out using sorption isotherms. The Langmuir model for individual gases and the extended Langmuir model for multicomponent gas mixtures were applied to fit sorption isotherm data. “Gas content derivative data” and “gas content changes” emerged as crucial mathematical parameters to accurately study the gas diffusion process. The main goal of this paper is to define the degree of interaction between the gas content derivative data and the gas diffusion process. Experiments were performed on three samples selected from two different coals, which were submitted to three different gas compositions, viz 99.999% CH4; 99.999% CO2; and a gas mixture containing 74.99% CH4 + 19.99% CO2 + 5.02% N2, at 35ºC, and at pressures ranging from 0 up to 50 bar. Experimental results obtained from the three samples indicate that during adsorption/desorption processes, the diffusion coefficients increase and the gas content changes decrease when the pressure decreases, due to the sample saturation degrees and to the kinetic mechanisms increase. Additionally, the “gas content derivative data” scattering is slightly lower during the desorption process than during the adsorption process. These behaviors are clearly identified when using methane, but are even more evident when using CO2 and the gas mixture, due to the CO2 interaction with coal porous structure, which induces a considerable resistance to CO2 release. The results show that sample B (CH4 + CO2 + N2) displays higher diffusion coefficient values (this behaviour is mainly related to the presence of N2) than sample C (CH4) and than Sample A (CO2).
- The role of coal “cleat system” in Coalbed Methane Prospecting/Exploring: A new approachPublication . Rodrigues, Cristina; Laiginhas, C.; Fernandes, M.; Lemos de Sousa, M. J.The Coalbed Methane (CBM) generated by coal is located in coal pores and the drainage of the coalbed gas to the production well is made through the so-called "cleat system", i.e., the natural fracture network of coal. This justifies the classic method of CBM production by providing fracture-stimulation with fluids under pressure to open coal natural fractures. However, natural fracturing system of any coal is very complex, depending on coalification process and local and regional tectonics. Additionally, the cleat network cannot be inferred using conventional regional micro-tectonics studies. Therefore, what really matters is to know, in each case, the spatial orientation of the different classes of fracturing, ordered by connectivity frequencies, to make possible an orientated injection of fluids to open the cleat permitting higher amounts of gas release/drainage. In fact, the cleat family of highest connectivity frequency is the one that define the gas circulation network to the producing well, and consequently the most favorable one to be opened by fluids injected in the correct direction. The current investigation refers to a new and innovative proposal to develop a method for determining cleat family orientation in the space, ordered by cleat connectivity frequency. This new semi-automatic method is based in the study of "cleat characteristics" by image analysis in orientated core samples of boreholes for CBM prospection/exploration. The information from image analysis is studied by statistical CCT ("coal-core tectonics") methodology and subsequently combined with Geographic Information System, thus referring to location of the real case under study.
- Documented international enquiry on solid sedimentary fossil fuels; Coal: definitions, classifications, reserves-resources and energy potentialPublication . Alpern, B.; Lemos de Sousa, M. J.This paper deals with all solid sedimentary fossil fuels, i.e. coal, the main one for geological reserves and resources, peat, and oil shales. Definitions of coal ( < 50% ash) and coal seam (thickness and depth limits) are examined in view of an international agreement regarding new concepts for a common reserves and resources evaluation using the same nomenclature. The 50% ash limit, already adopted by UN-ECE for coal definition, allows the creation of a new category—the organic shales (50–75% ash)—comprising energetic materials still valuable for thermal use (coal shales) or to be retorted for oil production (oil shales). Geological relations between coals, oil shales, solid bitumen, liquid hydrocarbons, natural gas, and coalbed methane are also examined together with environmental problems. As a final synthesis of all topics, the paper discusses the problems related with a modern geological classification of all solid sedimentary fuels based on: various rank parameters (moisture content, calorific value, reflectance), maceral composition, and mineral matter content (and washability). Finally, it should be pointed out that the paper is presented as series of problems, some of them old ones, but never resolved until now. In order to facilitate the next generation of coal geologists to resolve these problems on the basis of international agreements, all sections begin with documented introductions for further questions opening an international enquiry. The authors hope that the answers will be abundant enough and pertinent to permit synthetic international solutions, valuable for the new millennium, with the help of interested consulted authorities, international pertinent organisations, and regional experts. D 2002 Elsevier Science B.V. All rights reserved.