Solid bitumen as an indicator of petroleum migration, thermal maturity, and contact metamorphism: A case study in the Barrandian Basin (Silurian - Devonian), Czech Republic

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
Václav Suchý , Ivana Sýkorová , Jiří Zachariáš , Kateřina Pachnerová Brabcová , Petr Dobeš , Martina Havelcová , Ivan Rozkošný , Qingyong Luo , Weixun Cao , Jin Wu , Petra Mácová , Alberto Viani , Ivo Svetlik , Daniel Maxa
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引用次数: 0

Abstract

Silurian and Devonian marine shales and limestones of the Barrandian Basin host abundant black solid, non-fluorescing bitumens that fill tectonic fractures and veins, and occlude fossil moulds and diagenetic concretions. Solid bitumen, interpreted as thermally degraded petroleum, entered the rocks during several successive episodes of fracture-bound petroleum migration that occurred during deeper burial of the strata. Regional distribution of bitumen reflectance values that range between ∼0.9–2.3% Rr, correlate with variations of its FT-IR and Raman spectroscopic characteristics and aromatic hydrocarbon composition, and collectively evidence the maturity trend increasing across the basin from the southwest to the northeast. The reflectance of chitinozoans and graptolites (∼0.8–1.9% Rr) in the country rocks and homogenization temperatures of hydrocarbon fluid inclusions document palaeotemperatures ranging between ∼90–150 °C, characteristic of the oil window zone grading into the gas/condensate zone. Although in a basin-wide perspective the averaged values of solid bitumen and zooclast optical reflectance converge and indicate the same northeastern-increasing regional diagenetic trend, solid bitumen reflectance values vary considerably at individual localities and even within some bitumen samples. The wide scatter of optical reflectance values and the heterogeneity of optical properties, which were attributed to the presence of multiple source rocks in the basin, the variable lithology of bitumen host rocks, or other variables, hamper the use of solid bitumen as a simple alternative to zooclast/vitrinite reflectance palaeothermometers in a given basin. On the other hand, the highly anisotropic domain and the mesophase “coking” textures of the solid bitumen that were recognized in the NE part of the basin provide unique evidence on an anomalous, hitherto unrecognized, geologically short-lasting thermal event that affected the Palaeozoic rocks. A line of indirect evidence suggests that the coking of the bitumen was caused by a cryptic intrusion, possibly a concealed branch of the Central Bohemian Pluton, which intruded into the strata during the Variscan orogeny. More rarely occurring semi-solid, vividly yellow fluorescing waxy bitumen, that postdates solid bitumen in some fractures and voids, does not reveal a regional thermal maturation trend. It precipitated from relict waxy oils that migrated through the strata during a post-Neogene uplift of the Barrandian region.

固体沥青作为石油迁移、热成熟度和接触变质作用的指标:捷克共和国巴兰盆地(志留纪-泥盆纪)案例研究
巴兰盆地的志留纪和泥盆纪海相页岩和灰岩中蕴藏着大量黑色固态非荧光沥青,这些沥青填充了构造裂缝和岩脉,并遮蔽了化石模和成岩凝块。固态沥青被解释为热降解石油,是在地层深埋过程中发生的几次连续的裂缝石油迁移过程中进入岩石的。沥青反射率的区域分布在 ~0.9-2.3% R 之间,与沥青的傅立叶变换红外光谱和拉曼光谱特征以及芳香烃成分的变化相关,共同证明了成熟度在盆地内从西南向东北递增的趋势。乡土岩中壳虫和爬行岩的反射率(~ 0.8-1.9% R)以及烃类流体包裹体的均质化温度记录了~90-150 °C之间的古温度,这是石油窗口区向天然气/凝析气区分级的特征。虽然从整个盆地的角度来看,固体沥青和动物沉积物光学反射率的平均值趋于一致,并显示出相同的东北向区域成岩趋势,但固体沥青的反射率值在个别地方甚至在某些沥青样本中存在很大差异。由于盆地中存在多种源岩、沥青主岩的岩性多变或其他变量,光学反射率值的巨大差异和光学性质的异质性阻碍了在特定盆地中使用固体沥青作为动物群/岩性反射率古温度计的简单替代方法。另一方面,在盆地东北部发现的固体沥青的高度各向异性域和介相 "焦化 "纹理,为影响古生代岩石的异常的、迄今未被发现的、地质学上持续时间短的热事件提供了独特的证据。一系列间接证据表明,沥青焦化是由一个隐秘的侵入体造成的,该侵入体可能是中波西米亚岩块的一个隐蔽分支,在瓦里斯坎造山运动期间侵入地层。在一些断裂和空隙中,半固态、鲜黄色荧光蜡状沥青的出现时间晚于固态沥青,但这种沥青很少出现,并没有显示出区域性的热成熟趋势。它析出自巴兰迪地区新近纪后隆起过程中通过地层迁移的残余蜡油。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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