南非卡鲁中部粗玄岩岩床和火山口的地震成像:对页岩气潜力的影响

IF 1.2 4区 地球科学 Q2 GEOLOGY
Stephanie Scheiber-Enslin, M. Manzi, S. Webb
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引用次数: 3

摘要

南非卡鲁盆地占地70万平方公里,已被确定为可能的页岩气储量。对盆地页岩气潜力的任何评估都必须考虑广泛分布的粗玄岩脉和岩床。这些侵入体侵位于卡鲁超群,年代约为183Ma。它们的侵入引发了盆地内气体的爆炸性释放,地表以角砾岩管道和热液喷口为标志。这种天然气的泄漏被认为是全球气候变化的一个重要因素。对这些粗玄岩岩床和岩墙的三维互连结构及其与卡鲁超群下部富烃层的相互作用的研究仅限于对露头、磁性数据、遗留地震数据(20世纪70年代)和岩芯的局部观测。在这里,我们展示了一个65公里长、分辨率更高的二维地震反射剖面,该剖面位于特罗姆斯堡东南约100公里处的卡鲁盆地。这些数据是在20世纪90年代收集的,当时对沿线更深的结构进行了解释。在这项研究中,我们关注的是数据的前0.6到2秒行波管。地震线显示了沿剖面的粗玄岩脉和岩床的相互连接和交叉性质。我们还报告了可能的证据,表明在怀特希尔组附近的粗玄岩岩床边缘出现了气体逸出结构(表面直径约2.5公里),怀特希尔组是页岩气勘探的主要目标。这表明靠近莱索托的卡鲁盆地东部的天然气喷口是由于Ecca群碳质页岩释放出的气体。这与卡鲁盆地西部地表绘制的角砾岩管道相似。该地震剖面强调了在评估卡鲁盆地页岩气潜力时必须考虑粗玄岩岩床和岩墙的原因。我们建议,在计算页岩气储量之前,有必要通过地震和磁学研究对卡鲁盆地地下进行更好的表征。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Seismic imaging of dolerite sills and volcanic vents in the Central Karoo, South Africa: implications for shale gas potential
The Karoo Basin of South Africa covers an area of 700 000 km2 and has been identified as a possible shale gas reserve. Any evaluation of the shale gas potential of the basin must consider the widespread dolerite dykes and sills. These intrusions were emplaced into the Karoo Supergroup and are well dated at around 183 Ma. Their intrusion triggered the explosive releases of gas in the basin, marked on surface by breccia pipes and hydrothermal vents. This outpouring of gas has been proposed as a significant contributor to global climate change. Research into the three-dimensional interconnected structure of these dolerite sills and dykes and their interaction with the hydrocarbon rich layers in the lower part of the Karoo Supergroup has been limited to localized observations of outcrop, magnetic data, legacy seismic data (from the 1970s) and well core. Here we present an interpreted 65 km long higher-resolution 2D seismic reflection profile across the Karoo Basin, approximately 100 km southeast of Trompsburg. These data were collected in the 1990s and at the time deeper structures along the line interpreted. In this study we focus on the top 0.6 to 2 seconds TWT of the data. The seismic line images the interconnected and cross cutting nature of the dolerite dykes and sills along the profile. We also report possible evidence of a gas escape structure (approximately 2.5 km in diameter at surface) emerging near the edge of a dolerite sill in close proximity to the Whitehill Formation, which is the main target for shale gas exploration. This suggests that gas vents in the eastern Karoo Basin close to Lesotho are due to the release of gas from the carbonaceous shales of the Ecca Group. This is similar to breccia pipes mapped on surface in the western part of the Karoo Basin. This seismic section highlights why dolerite sills and dykes must be considered when evaluating the shale gas potential of the Karoo Basin. We propose that better characterization of the Karoo Basin subsurface by seismic and magnetic studies is necessary prior to any efforts to calculate shale gas reserves.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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