A naturally fractured chalk reservoir in the Ekofisk Formation: characteristics, petrography and stable isotope signature of cemented fractures and faults (The Kraka Field, Danish North Sea)

IF 0.8 4区地球科学 Q2 Earth and Planetary Sciences

Norwegian Journal of Geology Pub Date : 2020-06-19 DOI:10.17850/njg100-2-4

A. C. Glad, F. Amour, M. Welch, O. Clausen, H. Nick

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引用次数: 2

Abstract

Natural fractures occur in chalk from the Kraka Field (Danian Ekofisk Formation, Southern Danish Sea) and contribute to an increased effective permeability in the reservoir. The majority of fractures are open and act as conduits for hydrocarbons to migrate through. However, some fractures are cemented and thus act as barriers for fluid flow. Predicting porosity and fluid flow in subsurface carbonate reservoirs is challenging, and with a proper understanding of cementation in fractures these subjects are better understood. Further knowledge on cemented fractures can be useful for hydrocarbon exploration and production. This study investigates cemented fractures, faults and a cataclastic fault zone in chalk cores from the Kraka Field. Emphasis is given to small-scale fractures. These are either partially or fully cemented by mineral precipitates, commonly calcite, and have apparent widths of up to 5 mm. One type of fractures has silica cement along the fracture edge and calcite in the central part, while another type only contains blocky calcite cement. The faults have apparent widths up to 5 cm and are partially cemented by calcite. The cataclastic fault zone has an apparent width of 25 cm and is filled with angular fragments of chalk cemented by blocky calcite. Stable isotope analysis of the cement in the fractures and the cataclastic fault zone suggests that they were filled by calcite cement almost simultaneously during burial. The paragenetic sequence of Danian chalk from the Kraka Field is reconstructed and compared with that of other North Sea fields. Based on an investigation of cemented fractures in the Kraka Field, this study provides information on cementation evolution and possible implications for porosity and fluid flow. The majority of Danish faults, and one example of a cataclastic fault zone. The distinction between fractures

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Ekofisk组天然裂缝白垩岩储层：胶结裂缝和断层的特征、岩石学和稳定同位素特征（丹麦北海克拉卡油田）

天然裂缝出现在Kraka油田（丹麦海南部Danian Ekofisk组）的白垩中，有助于提高储层的有效渗透率。大多数裂缝是开放的，充当碳氢化合物迁移的管道。然而，一些裂缝被胶结，从而成为流体流动的屏障。预测地下碳酸盐岩储层的孔隙度和流体流动具有挑战性，如果对裂缝中的胶结有了正确的理解，这些主题就会更好地理解。进一步了解胶结裂缝可能对油气勘探和生产有用。本研究调查了克拉卡油田白垩岩岩芯中的胶结裂缝、断层和碎裂断层带。重点是小规模裂缝。这些裂缝由矿物沉淀物（通常为方解石）部分或完全胶结，表观宽度高达5毫米。一种类型的裂缝沿裂缝边缘有硅石胶结物，中部有方解石，而另一种类型仅含有块状方解石胶结物。断层的表观宽度高达5厘米，部分由方解石胶结。碎裂断层带的表观宽度为25厘米，充满了由块状方解石胶结的白垩角碎片。对断裂和碎裂断裂带中胶结物的稳定同位素分析表明，在埋藏过程中，它们几乎同时被方解石胶结物填充。重建了克拉卡油田大年白垩系的共生序列，并与北海其他油田的共生序列进行了比较。基于对克拉卡油田胶结裂缝的调查，本研究提供了胶结演化的信息以及对孔隙度和流体流动的可能影响。大多数丹麦断层，以及碎裂断层带的一个例子。骨折之间的区别

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来源期刊

Norwegian Journal of Geology 地学-地球科学综合

CiteScore

1.60

自引率

25.00%

发文量

审稿时长

>12 weeks

期刊介绍： The Norwegian Journal of Geology publishes high-quality, fully peer-review papers from all geoscientific disciplines. Papers are commonly based on regional studies and should emphasise the development of understanding of fundamental geological processes. More specialised papers can also be submitted, but should be written in a way that is easily understood by nonspecialists, and illustrate the progress being made within that specific topic in geosciences. We also encourage initiatives for thematic issues within the scope of the Journal.