Abstract
The aim of this study was to determine the coal characteristics in the Chico-Lomã coalfield, Brazil and to evaluate the potential of natural gas associated with the coal seams (CBM), by carrying out a test well (CBM001-CL-RS) for collecting coal samples, followed by gas desorption measurements, and petrographical and chemical analyses of the coals and their methane adsorption capacities. The gas collected was analyzed for gas composition, stable carbon and hydrogen isotopes. The results indicate a cumulative coal thickness of 11.46 m in well CBM001-CL-RS, associated with an igneous intrusion of 10 m thickness. In the contact zone with the intrusion, the organic matter is severely altered with partial transformation of the coal to natural coke at distances less than 2 m from the intrusion. The ash content, based on proximate analysis, shows a variation from 29.1 to 82.8 wt.%. The sulphur content ranges from 0.43 to 3.89 wt.% and shows higher values in samples from the top of the Rio Bonito Formation. The gas desorption measurements range from 0.05 to 0.74 cm3/g, with methane being the predominant gas (>90%). A thermal origin of the gas is suggested by C and H isotopes and the C1 (methane) to C3 (propane) hydrocarbon distribution. The methane adsorption capacity of the samples varies from 2.50 to 6.50 cm3/g. Changes in microporosity related to thermal alteration may have a significant impact on the gas-holding capacity of samples located near the contact to the intrusion. For the study area, a 3D geological model was generated to estimate the volume of coal in the coalfield, followed by assessment of the gas volume associated with the coal. Based on the 3D model, a preliminary appraisal indicates resources of 7.2 billion tons of coal for the Chico-Lomã coalfield, associated with 2.7 billion m3of gas.
Highlights
Despite the focus on shale gas exploration and exploitation in recent years, CBM resources remain an important source of none-conventional gas (Mastalerz, 2014), with a total of 250 Â 1015 m3 estimated worldwide (Murray, 1996).In Brazil, economically important coal-measures occur in the southern part of the Parana Basin (Figure 1), covering portions of Rio Grande do Sul, Santa Catarina and Paranastates, with measured reserves in the order of 32 billion tons of coal (Informativo Anual da Industria Carbonıfera, 2000)
The Coal and Source Rock Laboratories, Universidade Federal do Rio Grande do Sul (UFRGS) have been evaluating for a number of years the CBM potential of the Brazilian coal deposits based on parameters such as depth of coal-bearing interval, coal rank and coal seam distribution (Kalkreuth and Holz, 2000; Kalkreuth et al, 2003, 2006, 2010, 2013)
The present study focuses on the evaluation of the CBM potential in the Chico-Lom~a Coalfield, RS (Figure 1), based on the results of gas desorption measurements on coal samples retrieved from a CBM exploration borehole (CBM001-CL-RS)
Summary
Despite the focus on shale gas exploration and exploitation in recent years, CBM resources remain an important source of none-conventional gas (Mastalerz, 2014), with a total of 250 Â 1015 m3 estimated worldwide (Murray, 1996).In Brazil, economically important coal-measures occur in the southern part of the Parana Basin (Figure 1), covering portions of Rio Grande do Sul, Santa Catarina and Paranastates, with measured reserves in the order of 32 billion tons of coal (Informativo Anual da Industria Carbonıfera, 2000). Despite the focus on shale gas exploration and exploitation in recent years, CBM resources remain an important source of none-conventional gas (Mastalerz, 2014), with a total of 250 Â 1015 m3 estimated worldwide (Murray, 1996). The Coal and Source Rock Laboratories, Universidade Federal do Rio Grande do Sul (UFRGS) have been evaluating for a number of years the CBM potential of the Brazilian coal deposits based on parameters such as depth of coal-bearing interval, coal rank and coal seam distribution (Kalkreuth and Holz, 2000; Kalkreuth et al, 2003, 2006, 2010, 2013). The present study focuses on the evaluation of the CBM potential in the Chico-Lom~a Coalfield, RS (Figure 1), based on the results of gas desorption measurements on coal samples retrieved from a CBM exploration borehole (CBM001-CL-RS) CBM exploration boreholes (Figure 1) have been carried out in the Santa Terezinha Coalfield, Rio Grande do Sul (Kalkreuth et al, 2008, 2013) and in the South Santa Catarina Coalfield, Santa Catarina (Lourenzi et al, 2017), with the highest CBM potential determined for the Santa Terezinha Coalfield.
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