Akintola George Oluwole, Amponsah-Dacosta Francis, Rupprecht Steven, Mhlongo Sphiwe Emmanuel
Department of Earth Sciences, Faculty of Science, Engineering and Agriculture, University of Venda, Private Bag X5050 Thohoyandou 0950 Limpopo Province South Africa.
Department of Mining Engineering, University of Johannesburg, Johannesburg 2006, South Africa.
Heliyon. 2023 Mar 11;9(3):e14446. doi: 10.1016/j.heliyon.2023.e14446. eCollection 2023 Mar.
The transition to a low-carbon energy source from coal has become imperative to mitigating the escalating climate change crisis. This study aims to investigate the organic-rich shale core samples of the Limpopo-Area Karoo Basin, retrieved from the borehole at depth 480-580 m. These samples were subjected to petrographic, mineralogical, morphological, and kerogen-type analysis to investigate potentials for shale gas generation. The petrographic analysis reveals maceral group mainly comprised of vitrinite group with some liptinite and inertinite and mineral compositions. The preponderance of pyrite framboids (1.6-12%) indicate redox of FeS as a precursor to methane gas generation in anoxic condition. The x-ray diffractometer (XRD) reveals the presence of quartz, albite, microcline, dolomite, pyrite and clay minerals which alluded to the mineral composition indicated by the petrographic analysis. The clay mineral component consists of montmorillonite, illite, chlorite, and mixed layered illite/smectite (I/S) in the Madzaringwe samples. The representative scanning electron microscopy-Energy Dispersive X-ray (SEM-EDX) images of the studied shales depict a combination of organic-matter, groundmass mineral, micro-fracture pore structures reflecting polyframboidal pyrite and carbonate dissolution morphology. The total organic carbon (TOC) contents averaging at 47 wt%, indicating an excellent source rock. The Rock-Eval 6 programmed pyrolysis samples showed S2 value (15.25-16.47 mg HC/g rock) with an average of 15.69 mg HC/g rock and Hydrogen index (HI) (34.0-37.0 mg HC/g TOC) indicating a Type-III Kerogen dominance prone to gas generation. The shale showed Tmax values (464-470 °C) averaging at 467.2 °C, yielding a thermally mature condensate wet-gas. This study reveals that the Permian carbonaceous rock tends to generate gas which can be hosted mainly by the organic matter pore structures, inorganic and micro-fracture pore structures.
从煤炭向低碳能源的转型对于缓解不断升级的气候变化危机已变得势在必行。本研究旨在调查从深度480 - 580米的钻孔中获取的林波波地区卡鲁盆地富含有机质的页岩岩芯样本。对这些样本进行了岩相学、矿物学、形态学和干酪根类型分析，以研究页岩气生成的潜力。岩相学分析表明，显微组分主要由镜质组组成，还有一些壳质组和惰质组以及矿物成分。大量的黄铁矿莓球（1.6 - 12%）表明FeS的氧化还原是缺氧条件下甲烷气体生成的前体。X射线衍射仪（XRD）显示存在石英、钠长石、微斜长石、白云石、黄铁矿和粘土矿物，这证实了岩相学分析所表明的矿物成分。在马扎林韦样本中，粘土矿物成分包括蒙脱石、伊利石、绿泥石以及混合层伊利石/蒙脱石（I/S）。所研究页岩的代表性扫描电子显微镜 - 能量色散X射线（SEM - EDX）图像描绘了有机质、基质矿物、反映多莓球黄铁矿和碳酸盐溶解形态的微裂缝孔隙结构的组合。总有机碳（TOC）含量平均为47 wt%，表明是优质烃源岩。岩石热解6程序热解样本显示S2值（15.25 - 16.47毫克HC/克岩石），平均为15.69毫克HC/克岩石，氢指数（HI）（34.0 - 37.0毫克HC/克TOC）表明以III型干酪根为主，易于产气。页岩的Tmax值（464 - 470°C）平均为467.2°C，产生热成熟的凝析湿气。本研究表明，二叠纪碳质岩倾向于产气，气体主要储集于有机质孔隙结构、无机孔隙结构和微裂缝孔隙结构中。
