Browsing by Author "Fernandes, M."
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- The coal cleat system: A new approach to its studyPublication . Rodrigues, Cristina; Laiginhas, C.; Fernandes, M.; Lemos de Sousa, M. J.; Dinis, Maria Alzira PimentaAfter a general analysis regarding the concept of coal “cleat system!”, its genetic origin and practical application in Coalbed methane (CBM) commercial production and in CO2 geological sequestration projects, the authors have developed a method to answer, quickly and accurately according with the industrial practice and needs, to the following yet unanswered questions: (i) how to define the spatial orientation of the different classes of cleats present in a coal seam, and (ii) how to determine the frequency of their connectivites? The new available and presented techniques to answer these questions have a strong computer based tool (Geographic Information System (GIS)), able to build a complete georeferentiated database, which will allow to three-dimensionally locate the laboratory samples in the coalfield. It will also allow to better understand the coal cleat system and consequently to recognise the best pathways to gas flow through the coal seam. Such knowledge is considered crucial for understanding what is likely to be the most efficient opening of cleat network, then allowing the injection with the right spatial orientation, of pressurized fluids or propants in order to directly drain the maximum amount of gas flow to a CBM exploitation well. The method is also applicable to the CO2 Geological Sequestration Technologies, operations corresponding to the injection of CO2 sequestered from industrial plants in coal seams of abandoned coalmines or high depth coal seams.
- 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.