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首页> 外文期刊>Organic Geochemistry: A Publication of the International Association of Geochemistry and Cosmochemistry >Organic geochemistry and petrology of subsurface Paleocene-Eocene Wilcox and Claiborne Group coal beds, Zavala County, Maverick Basin, Texas, USA
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Organic geochemistry and petrology of subsurface Paleocene-Eocene Wilcox and Claiborne Group coal beds, Zavala County, Maverick Basin, Texas, USA

机译：美国德克萨斯州马弗里克盆地扎瓦拉县地下新世-始新世Wilcox和Claiborne Group煤层的有机地球化学和岩石学

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摘要

Coal samples from a coalbed methane exploration well in northern Zavala County, Maverick Basin, Texas, were characterized through an integrated analytical program. The well was drilled in February, 2006 and shut in after coal core desorption indicated negligible gas content. Cuttings samples from two levels in the Eocene Claiborne Group were evaluated by way of petrographic techniques and Rock-Eval pyrolysis. Core samples from the Paleocene-Eocene Indio Formation (Wilcox Group) were characterized via proximate-ultimate analysis in addition to petrography and pyrolysis. Two Indio Formation coal samples were selected for detailed evaluation via gas chromatography, and Fourier transform infrared (FTIR) and ~(13)C CPMAS NMR spectroscopy. Samples are subbituminous rank as determined from multiple thermal maturity parameters. Elevated rank (relative to similar age coal beds elsewhere in the Gulf Coast Basin) in the study area is interpreted to be a result of stratigraphic and/or structural thickening related to Laramide compression and construction of the Sierra Madre Oriental to the southwest. Vitrinite reflectance data, along with extant data, suggest the presence of an erosional unconformity or change in regional heat flow between the Cretaceous and Tertiary sections and erosion of up to >5km over the Cretaceous. The presence of liptinite-rich coals in the Claiborne at the well site may indicate moderately persistent or recurring coal-forming paleoenvironments, interpreted as perennially submerged peat in shallow ephemeral lakes with herbaceous and/or flotant vegetation. However, significant continuity of individual Eocene coal beds in the subsurface is not suggested. Indio Formation coal samples contain abundant telovitrinite interpreted to be preserved from arborescent, above-ground woody vegetation that developed during the middle portion of mire development in forested swamps. Other petrographic criteria suggest enhanced biological, chemical and physical degradation at the beginning and end of Indio mire development. Fluorescence spectra of sporinite and resinite are consistent and distinctly different from each other, attributed to the presence of a greater proportion of complex asphaltene and polar molecules in resinite. Gas chromatography of resinite-rich coal shows sesquiterpenoid and diterpenoid peaks in the C _(14-17) range, which are not present in resinite-poor coal. Quantities of extracts suggest bitumen concentration below the threshold for effective source rocks [30-50mg hydrocarbon/g total organic carbon (HC/g TOC)]. Saturate/aromatic and pristane/phytane (Pr/Ph) ratios are different from values for nearby Tertiary-reservoired crude oil, suggesting that the Indio coals are too immature to source liquid hydrocarbons in the area. However, moderately high HI values (200-400mg HC/g rock) may suggest some potential for naphthenic-paraffinic oil generation where buried more deeply down stratigraphic/structural dip. Extractable phenols and C _(20+) alkanes are suggested as possible intermediates for acetate fermentation in microbial methanogenesis which may, however, be limited by poor nutrient supply related to low rainfall and meteoric recharge rate or high local sulfate concentration.
机译：通过综合分析程序对德克萨斯州马弗里克盆地Zavala县北部煤层气勘探井中的煤样品进行了表征。该井于2006年2月进行了钻探，并在煤芯解吸表明可忽略不计的瓦斯含量后关闭。始新世克莱伯恩组两个层面的岩屑样品通过岩相学技术和岩石评价热解法进行了评估。除岩相学和热解作用外，还通过近距离-最终分析对古新世-始新世印第纪地层（Wilcox集团）的岩心样品进行了表征。选择了两个Indio地层煤样品进行气相色谱，傅里叶变换红外（FTIR）和〜（13）C CPMAS NMR光谱进行详细评估。根据多个热成熟度参数确定的样品为次烟级。研究区的煤阶升高（相对于墨西哥湾沿岸盆地其他地区的类似年龄的煤层）被认为是与拉拉米德压缩和西南山脉马德雷东方构造有关的地层和/或构造增厚的结果。玻璃铁矿的反射率数据以及现存的数据表明，白垩纪和第三纪之间存在侵蚀不整合或区域热流变化，并且白垩纪的侵蚀长达5km以上。克莱伯恩（Claiborne）井场中富立陶土富煤的存在可能表明存在中等持久性或重复性的成煤古环境，这被解释为多年生草本植物和/或浮游植物的浅临时湖中的泥炭。然而，地下的各个始新世煤层没有明显的连续性。印第奥岩层煤样品中含有丰富的钙钛铁矿，据解释是从森林沼泽中泥潭发展的中部所形成的树状地上木本植被中保存下来的。其他岩相学标准表明，在印第奥泥矿开发的开始和结束时，生物，化学和物理降解加剧。子锂辉石和树脂岩的荧光光谱是一致的，并且彼此明显不同，这归因于树脂岩中存在更多比例的复杂沥青质和极性分子。富含树脂的煤的气相色谱显示在C _（14-17）范围内的倍半萜和二萜的峰，在贫树脂的煤中不存在。提取物的数量表明沥青浓度低于有效烃源岩的阈值[30-50mg碳氢化合物/ g总有机碳（HC / g TOC）]。饱和/芳香族和p烷/植烷（Pr / Ph）之比与附近的三次储层原油的值不同，这表明印第欧煤还不成熟，无法在该地区获得液态烃。但是，中等偏高的HI值（200-400mg HC / g岩石）可能表明某些潜在的环烷烃石蜡油的产生，埋藏在地层/构造倾角的更深处。建议将可提取的酚和C_（20+）烷烃作为微生物甲烷生成中醋酸盐发酵的可能中间体，但是可能会受到与低降雨和大气补给速率或高局部硫酸盐浓度相关的营养供应不足的限制。

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