Browsing by Author "Rodrigues, Cristina"
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- O Carvão na ActualidadePublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Dinis, Maria Alzira Pimenta
- 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.
- Coal gas adsorption/desorption isotherms versus diffusion processPublication . Rodrigues, Cristina; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.In the present work, the authors studied two meta-anthracite samples from Douro Coalfield (NW of Portugal) in which classical sorption isotherms were carried out, using CO2 only. Results have demonstrated that whenever the CO2 is adsorbed in the coal pores/matrix it will be enduringly fixed up to, approximately, pressures of 32 bar in sample A and 34 bar in sample B. Since the gas release process it intensely related to diffusion coefficients, it is crucial to define their evolution on the two analyses reported in this paper. So, during adsorption, diffusion coefficients decrease in sample A from 4.66736E-08 to 1.23490E-09 cm2/sec (6.72 and 48.13 bar) and during desorption they increase from 7.61829E-09 to 1.09908E-08 cm2/sec (45.68 and 11.48 bar). In sample B, diffusion coefficients decrease from 2.47409E-08 to 2.11813E-09 cm2/sec (7.53 and 47.17 bar) in adsorption and increase in desorption from 1.48767E-09 to 2.83736E-08 cm2/sec (42.22 and 7.71 bar).
- 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.
- 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.
- Estudio de las propiedades de adsorción/desorción de gas en el carbón de la Cuenca de Sabinas en México: Study of gas adsorption/desorption properties in coals of Sabinas Basin on MexicoPublication . Enciso-Cárdenas, J. J.; Rodrigues, Cristina; Martínez, L.; Camacho-Ortegón, L. F.; Lemos de Sousa, M. J.; De la O-Burrola, F.; Dinis, Maria Alzira PimentaEl objetivo principal de esta investigación, se enfoca en el estudio de las propiedades de adsorción/desorción de CH4 en los yacimientos de gas asociado al carbón, los cuales se ubican en la porción noreste de México, con el fin de comprender su comportamiento desde el punto de vista de los yacimientos no convencionales. Para continuar con el desarrollo de este proyecto, se llevó a cabo una campaña de muestreo a cargo del Servicio Geológico Mexicano (SGM), el cual nos proporcionó 7 muestras de carbón bituminoso, procedentes de la Cuenca de Sabinas para su caracterización. La caracterización general incluyó: (1) Análisis inmediatos o primarios de humedad y ceniza, (2) Análisis elemental para la determinación de (C, H, O, N, y S), (3) Análisis petrográfico para determinar el tipo de materia orgánica, (4) Pirolisis Rock-Eval®6 para conocer su potencial petrolífero. El conjunto de estos análisis nos permitieron evaluar las muestras para desarrollar mediante “Isotermas de Langmuir” los ensayos de adsorción/desorción de CH4 y la interpretación de los parámetros que influyen en el proceso de adsorción. Para el desarrollo de las pruebas de adsorción/desorción se utilizó la técnica termo-volumétrica, observando capacidades de almacenamiento de gas metano de 202.11 scf/ton (7.07m3/ton) a 364.76 scf/ton (10.47m3/ton). Estos resultados nos permitieron interpretar las características físicas y químicas que influyen en la capacidad de almacenamiento del gas en el carbón. Anticipando como conclusión general que: la adsorción del gas aumenta con el rango/madurez. También se estudió la influencia de la composición maceral en el proceso de sorción y se verificó que la capacidad de almacenamiento de gas está íntimamente relacionada al contenido de vitrinita. Esto nos condujo a retomar las declaraciones de algunos autores (Chalmers y Bustin, 2008; Zhang et al, 2012) quienes verificaron que la capacidad de adsorción en base al COT aumenta en el siguiente orden: tipo I < tipo II < tipo III. Esto se atribuyó a que la vitrinita tiene una mayor capacidad de adsorción, en comparación con otros tipos de macerales.
- 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).
- 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 Storage versus Gas Circulation in North Atlantic and Gondwana Coal TypesPublication . Dinis, Maria Alzira Pimenta; Rodrigues, Cristina; Lemos de Sousa, M. J.The growing insufficiency in oil and natural gas supplies and the rise in energy consumption all over the world have created new opportunities to other energy products and technologies. Coal acquired again an important role in the global energy survey. International Organizations are nowadays conscious and compromised to systematically move into Clean/Cleaner Coal Technologies (CCTs) and, above all, into Zero (or near zero) Emission Technologies (ZETs). Carbon Capture and Storage (CCS) Technologies, acting in a complementary way to CCTs, are becoming one of the solutions to face Climate Changes, permitting not to avoid but to minimize at an acceptable level the Green House Gas Effect (GHGE). It is also imperative to emphasize the actual crucial role of coal as a natural gas source rock and as a reservoir. Yet it is also important to understand that when coal has a high gas generation potential this fact does not necessarily imply that coal also has a high gas storage capacity and a high gas circulation performance. This investigation aims to compare the gas storage capacity and the gas circulation behaviour between Gondwana and North-Atlantic coal types. Two sets of Gondwana and North-Atlantic coal types, with different ranks, were selected in the present research. Results revealed that the two sets of samples, corresponding to different facies and, consequently, with different chemical and physical properties, have quite different gas storage and gas circulation behaviours. In general terms, “North-Atlantic Type” coals have a higher CH4 storage capacity than “Gondwana Type” coals, due to differences in their petrographic characteristics, mainly in terms of vitrinite content, and rank but also, although in a smaller scale, in terms of gas sorption temperatures. Diffusion coefficient values present a higher dependency on temperature changes than on gas storage capacities due to the high activation energy induced by high temperatures.
- II. Petrologia e Geoquímica OrgânicasPublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Dinis, Maria Alzira Pimenta
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