International Geologiical Congress - Oslo 2008


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GEP-17 Unconventional gas ? coalbed, shale, and tight gas-sands gases


Coalbed methane potential of Paraná Basin coals, Brazil - Results from test well CBM001 -ST-RS


Wolfgang Kalkreuth, Instituto de Geociencias, UFRGS (Brazil)
Michael Holz, Instituto de Geociencias, UFRGS (Brazil)
Junia Casagrande, Instituto de Geociencias, UFRGS (Brazil)
Tiago Oliveira, Instituto de Geociencias, UFRGS (Brazil)
Marcio Kern, Instituto de Geociencias, UFRGS (Brazil)
Janaina Levandowski, Instituto de Geociencias, UFRGS (Brazil)
Andreas Busch, RWTH Aachen University (Germany)
Bernhard Krooss, RWTH Aachen University (Germany)


On a worldwide scale methane resources associated with deep-lying coal beds (CBM) are estimated to range between 86 and 283 1012 m3. At present time methane is being produced from coal beds in a number of sedimentary basins in the USA and Canada, whereas in other countries such as China, Australia and India coalbed methane is one of the exploration targets of the petroleum industry. In Brazil the principal coal resources occur in the southern part of the Paraná Basin associated with the Permian age Rio Bonito Formation. Earlier studies identified the Santa Terezinha coalfield, Rio Grande do Sul (RS) as prime candidate for coalbed exploration in Brazil based on coal distribution (coal thickness, lateral continuities of the coal beds), size and depth of reservoir (coal) beds and coal rank)
The principal objectives of the present study were to develop a 3D geological model (Schlumberger Petrel) of the Santa Terezinha coalfield, focusing on an area of approx. 20 x 40 km in size, with depth of the coal-bearing interval ranging from 380 to 950 m, followed by a CBM test well to study the coal properties and to measure the desorbed methane volumes, in order to estimate the methane volumes contained in the deposit. The 3D modeling included seam correlation based on sequence stratigraphic interpretation, delineation of major fault systems, identification of diabase occurrences, as well as calculation of coal volumes for each stratigraphic unit identified.
The CBM test well was drilled in early 2007 near Osorio, RS, where samples from 12 coal seams and carbonaceous shales were collected from an interval of 605 to 638 m depth using wire line core retrieval techniques, followed by gas desorption tests and coal quality analyses Gas desorption values ranged from 0.37 to 2.01 cm3/g of coal (average value=0.95 cm3/g). Methane adsorption experiments carried out on selected samples suggest a methane adsorption capacity of up to 5 m3/t of coal. Methane constitute < 94 Vol% of the gas, with minor contributions of higher hydrocarbon homologues (ethane, propane, butane), CO2 and N2. Stable carbon isotope values indicate a thermal origin of the methane. The coals are in general mineral matter-rich (ash yields range from 28.4 to 92.7 wt.%) and are of high volatile bituminous rank, except where in contact with diabase (semi-anthracite).
Integration of coal volume determined by 3D modeling with average desorbed methane values suggest a total amount of 5 x 109 m3 of methane associated with the coal seams and carbonaceous shales for the study area investigated.


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