Ruilin Hao, Liyin Pan, Nana Mu, Xi Li, Xiaodong Fu, Shaoyun Xiong, Siqi Liu, Jianfeng Zheng, Min She, Axel Munnecke
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The foraminifera assemblage provides evidence that the studied interval is of Early Jurassic age. The δ13C values are similar to the contemporaneous seawater signature. The REE+Y patterns of limestones and dolostones exhibit similarities to that of seawater. The mean Na and Sr values are comparable to those of other near-normal seawater dolomites. The δ18O values of all lithologies are markedly depleted. The dolomitization started penecontemporaneously, with deposition. A general sand shoal setting with patch reefs developed. The dolomitizing fluids, near-normal seawater, was probably formed by slight evaporation on top of the shoal. Saddle dolomites in the interparticle and moldic pores might indicate hydrothermal activity, which also caused the recrystallization of some pre-existing dolomites. The recrystallization might have slightly increased the crystal size, demolished the ghost structures, formed saddle dolomites, and altered the REE+Y patterns. 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引用次数: 0
摘要
羌塘盆地(中国西南部)由块状白云岩组成的古油藏带的年龄和白云岩化过程仍存在争议。本研究选取了隆恩-格鲁盖纳地区。利用宏观信息、薄片和地球化学方法研究了白云岩化特征和控制白云岩化的过程。观察到了五种替代白云石和两种白云石胶结物。一些白云岩显示出原始沉积结构的幽灵。鞍状白云岩很普遍,出现在石灰岩的颗粒间隙和模孔中,这些孔隙应该在成岩早期就被填满了。确定了十种微地层类型。有孔虫的组合证明了所研究的区间属于早侏罗世。δ13C值与同期海水特征相似。石灰岩和白云石的 REE+Y 模式与海水相似。Na 和 Sr 的平均值与其他接近正常海水的白云岩相当。所有岩性的 δ18O 值都明显偏低。白云岩化与沉积同时开始。形成了带有片状礁石的总体沙滩环境。白云石化的流体是近乎正常的海水,可能是由浅滩顶部的轻微蒸发形成的。颗粒间和模孔中的鞍状白云石可能表明存在热液活动,这也导致了一些原有白云石的重结晶。重结晶可能使晶体尺寸略有增大,破坏了幽灵结构,形成了鞍状白云岩,并改变了 REE+Y 模式。再结晶的范围随着与提供流体的断裂距离的增加而减小。此外,沙洲环境中存在的保护区可能会增强白云岩储层的垂直和水平异质性。
Multi-Phase Dolomitization in the Jurassic Paleo-Oil Reservoir Zone, Qiangtang Basin (SW China): Implications for Reservoir Development
The age and dolomitization processes in the Paleo-oil reservoir zone, which is composed of massive dolostones found in the Qiangtang Basin (SW China), are still debated. In this research, the Long’eni-Geluguanna Area was selected. Macroscopic information, thin sections, and geochemical methods were used to investigate the dolomitization characteristics and the processes that controlled dolomitization. Five types of replacive dolomites and two types of dolomite cement were observed. Some of the dolomites displayed ghosts of primary sedimentary structures. Saddle dolomites were prevalent, occurring in the interparticle and moldic pores of the limestone which should have been filled at an early diagenetic stage. Ten microfacies types were identified. The foraminifera assemblage provides evidence that the studied interval is of Early Jurassic age. The δ13C values are similar to the contemporaneous seawater signature. The REE+Y patterns of limestones and dolostones exhibit similarities to that of seawater. The mean Na and Sr values are comparable to those of other near-normal seawater dolomites. The δ18O values of all lithologies are markedly depleted. The dolomitization started penecontemporaneously, with deposition. A general sand shoal setting with patch reefs developed. The dolomitizing fluids, near-normal seawater, was probably formed by slight evaporation on top of the shoal. Saddle dolomites in the interparticle and moldic pores might indicate hydrothermal activity, which also caused the recrystallization of some pre-existing dolomites. The recrystallization might have slightly increased the crystal size, demolished the ghost structures, formed saddle dolomites, and altered the REE+Y patterns. The recrystallization extent diminished with increasing distance from the fluids-providing fracture. Furthermore, the existence of protected areas within the sand shoal settings could enhance the vertical and horizontal heterogeneity of dolostone reservoirs.
期刊介绍:
Minerals (ISSN 2075-163X) is an international open access journal that covers the broad field of mineralogy, economic mineral resources, mineral exploration, innovative mining techniques and advances in mineral processing. It publishes reviews, regular research papers and short notes. Our aim is to encourage scientists to publish their experimental and theoretical results in as much detail as possible. There is no restriction on the length of the papers. The full experimental details must be provided so that the results can be reproduced.