The potential of CBM (Coalbed Methane) generation in the South Santa Catarina reserve: 1. petrographic and chemical characteristics of the coal seams in Rio Bonito Formation, Paraná Basin

Currently, CBM is an important source of alternative energy in Brazil. The most important coal bearing sedimentary succession occurs in the Paraná Basin, and the largest reserves are located in RS and SC. This work aims to analyze the chemical and petrological characteristics of coal seams from three boreholes, being recently conducted in the South Santa Catarina coalfield, in the areas of Treviso and Ararangua (SC), in order to assess the capacity to generate associated methane gas. Samples of seven coal seams were collected (Barro Branco, Irapuá, seam A, Bonito Superior, Bonito Inferior, Pré-Bonito Superior and Pré-Bonito Inferior) from the Rio Bonito Formation, and were prepared and submitted for petrographic and chemical analysis. The lithotype banded dull (BD) was prevalent in hole CBM-SC-2012, and dull (D) in hole CBM-SC-2013. Petrographic results indicated average vitrinite reflectance values from 0.60 to 1.26 % Rrandom, classifying the seams according to rank from high volatile bituminous C to medium volatile bituminous. Maceral analysis showed significant variation in maceral composition, with predominance of vitrinite and inertinite. Results from the proximate analysis showed ash variation from 34.93 to 65.70 wt%, whereas the gross calorific value varied from 1858.0 to 5074.8 cal/g. The carbon content ranged from 4.15 to 65.81 wt%, and sulfur ranged from 0.22 to 12.43%. According to the analyzed parameters, the Barro Branco and Irapuá seams present characteristics suitable for the generation of natural gas, whereas the Bonito seam has a lower gas generation potential because of its high ash content.当前，煤层气（Coal Bed Methane, CBM）是巴西重要的替代能源来源。该国最重要的含煤沉积序列赋存于巴拉那盆地（Paraná Basin），最大储量分布于RS与SC地区。本研究旨在分析圣卡塔琳娜州南部煤田特雷维索与阿拉朗瓜（SC）区域内近期施工的3个钻孔的煤层化学与岩石学特征，以评估其伴生甲烷气体的生成潜力。研究从里约博尼图组（Rio Bonito Formation）中采集了7个煤层样品，分别为Barro Branco、Irapuá、A煤层、Bonito Superior、Bonito Inferior、Pré-Bonito Superior以及Pré-Bonito Inferior，随后对样品进行制样并开展岩石学与化学分析。CBM-SC-2012孔的煤岩类型以条带暗淡煤（banded dull, BD）为主，CBM-SC-2013孔则以暗淡煤（dull, D）为主。岩石学分析结果显示，镜质体随机反射率（Rrandom）平均值介于0.60%至1.26%，据此将供试煤层的煤阶划分为高挥发分烟煤C级至中挥发分烟煤。显微组分分析结果表明，供试样品的显微组分组成存在显著差异，以镜质组与惰质组为主。工业分析结果显示，灰分质量分数介于34.93%至65.70 wt%，总热值介于1858.0至5074.8 cal/g。碳质量分数介于4.15%至65.81 wt%，硫质量分数介于0.22%至12.43%。基于上述分析参数，Barro Branco煤层与Irapuá煤层具备适宜的天然气生成特征，而Bonito煤层因灰分含量较高，产气潜力较低。