THE COALBED METHANE POTENTIAL OF THE PARANÁ BASIN IN RIO GRANDE DO SUL STATE, SOUTHERN BRAZIL

The southern region of Brazil, comprising Rio Grande do Sul, Santa Catarina and Paraná States, has been known for its abundant and economically important coalfields since the beginning of the century. The coal occurrences are historically assigned to the Rio Bonito Formation, a fluvial to marine sandstone and shale-prone unit of the Early Permian age Artinskian/Kungurian.

Total resources are in the order of 32 billions tons with the majority (89%) occurring in Rio Grande do Sul state. The study area is part of a tectonic unit in southwestern Gondwana known as the Paraná Basin, a large intracratonic basin located at the central-eastern part of the South-American Plate.

The coalfields selected for CBM evaluation are Santa Terezinha and Chico Lomã, RS that appear to have the highest CBM potential of the Paraná Basin coals (coal rank, coal distribution).

Coalbed methane potential was estimated based on coal resources, coal characteristics (coal quality and coal rank), coal distribution and thickness of individual coal seams, total coal thickness, size of reservoir, depth of the reservoir, hydrologic and tectonic regime, type of roof and base rock and partings. In addition, methane isotherm experiments on selected core samples were carried out to determine the methane adsorption capacities of the coals using standardized procedures (temperature, pressure and time).

The coal seams of the Santa Terezinha and Chico Lomã Coalfields occur in a depth interval from 400-950 m, with coal resources in the order of 4.2 billions tons for the three main seams and it has been suggested that there may be as much as 19 billions cubic meters coalbed methane associated with these.

Coal rank determination at this point is based on vitrinite reflectance measurements of 120 coal samples obtained from 30 boreholes. The reflectance values (0.53-0.99% Rrandom) indicate subbituminous to high volatile A bituminous coals. Locally diabase intrusions have altered the rank of the coal seams to anthracite, with vitrinite reflectances of up to 5,46%.

Current work focuses on 3D geological modeling of the deposit to determine the exact coal volume and to predict the CBM content based on the criteria mentioned above. Preliminary results will be presented at the time of the meeting.