Chlorite is recognized as a key mineral for preserving reservoir quality in deeply buried sandstones, as chlorite coatings inhibit the nucleation of quartz overgrowths. A limited understanding of the mechanisms and conditions under which these authigenic chlorite coatings form prevents the accurate forward modeling of diagenesis and limits reservoir quality models critical to a wide range of geoscience applications. We present experimental data that show how authigenic chlorite grain coatings preserve porosity in deeply buried sandstone reservoirs, using a series of hydrothermal reactor experiments to simulate quartz cementation and capture the evolving porosity. To simulate reservoir evolution, berthierine-bearing sandstone samples (Lower Jurassic Cook Formation, Oseberg Field, 30/6-17R, Norway) were exposed to a silica-supersaturated Na2CO3 (0.1 M) solution for 72 hours at temperatures of between 100 and 250 °C. Quantification of the temperature-dependent changes in the volume of authigenic chlorite, the thickness and coverage of the clay coatings, and the sample porosity shows increases in chlorite volume (from ∼ 2% to ∼ 14%). This occurs by the transformation, of patchy amorphous berthierine into grain-coating Fe-chlorite cements through a mixture of the solid-state transformation and dissolution–precipitation mechanisms, siderite replacement, and direct precipitation on clay-free surfaces. With increasing temperature, the chlorite coatings increase from ∼ 3.8 μm to ∼ 5.4 μm thick and expand their grain surface coverage from ∼ 28% to ∼ 50%. The face-to-edge and face-to-face foliaceous structure of the clay coatings produced are morphologically similar to those observed in deeply buried sandstones. Only above temperatures of 175 °C is porosity preserved as a consequence of inhibition of quartz overgrowths and the generation of secondary porosity.Our quantitative approach enhances our knowledge regarding the temperature and mineral precursor influence on chlorite-coating authigenesis and therefore provides key insight for chlorite grain coatings for reservoir potential in sedimentary sequences greater than 2.5 km.

中文翻译：

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亚氯酸盐成矿作用及其对砂岩孔隙率维持影响的实验研究

亚氯酸盐被认为是维护深埋砂岩中储层质量的关键矿物，因为亚氯酸盐涂层抑制了石英过度生长的形核。对这些自生亚氯酸盐涂层形成机理和条件的了解有限，妨碍了成岩作用的精确正演模拟，并限制了对广泛的地球科学应用至关重要的储层质量模型。我们提供的实验数据表明，使用一系列热液反应器实验来模拟石英胶结并捕获正在演化的孔隙度，自生的亚氯酸盐颗粒涂层如何在深埋的砂岩储层中保持孔隙度。为了模拟储层演化，将含黄连素的砂岩样品（下侏罗纪库克组，Oseberg油田，30 / 6-17R，挪威）暴露于二氧化硅超饱和的Na2CO3（0。1 M）溶液在100至250°C的温度下放置72小时。对自生绿泥石的体积，黏土涂层的厚度和覆盖率以及样品孔隙率随温度的变化进行量化，结果表明绿泥石的体积有所增加（从约2％增至约14％）。这是通过固态转化和溶解-沉淀机制，菱铁矿置换以及在无黏土表面上直接沉淀的混合物，将片状无定形的berthierine转变成颗粒包覆的Fe-亚氯酸盐水泥而发生的。随着温度的升高，亚氯酸盐涂层的厚度从〜3.8μm增加到〜5.4μm，其颗粒表面覆盖率从〜28％扩展到〜50％。所产生的粘土涂层的面对面和面对面的叶状结构在形态上与在深埋砂岩中观察到的相似。由于抑制了石英的过度生长和二次孔隙的产生，因此只有在高于175°C的温度时才能保留孔隙。我们的定量方法增强了我们对温度和矿物前驱物对绿泥石涂层成矿作用的认识，从而为绿泥石提供了重要的见识。大于2.5 km的沉积层中具有潜在储层的颗粒涂层。