Diagenetic illite growth in porous sandstones leads to significant modifications of the initial pore system which result in tight reservoirs. Understanding and quantifying these changes provides insight into the porosity-permeability history of the reservoir and improves predictions on petrophysical behavior. To characterize the various stages of diagenetic alteration, a focused ion beam – scanning electron microscopy (FIB-SEM) study was undertaken on aeolian sandstones from the Bebertal outcrop of the Parchim Formation (Early Permian Upper Rotliegend group). Based on 3D microscopic reconstructions, three different textural types of illite crystals occur, common to many tight Rotliegend sandstones, namely (1) feldspar grain alterations and associated illite meshworks, (2) tangential grain coats, and (3) pore-filling laths and fibers. Reaction textures, pore structure quantifications, and numerical simulations of fluid transport have revealed that different generations of nano-porosity are connected to the diagenetic alteration of feldspars and the authigenic growth of pore-filling illites. The latter leads to the formation of microstructures that range from authigenic compact tangential grain coatings to highly porous, pore-filling structures. K-feldspar replacement and initial grain coatings of illite are composed primarily of disordered 1M_d illite whereas the epitaxially grown illite lath- and fiber-shaped crystals occurring as pore-filling structures are of the trans-vacant 1M_tv polytype. Although all analyzed 3D structures offer connected pathways, the largest reduction in sandstone permeability occurred during the initial formation of the tangential illite coatings that sealed altered feldspars and the subsequent growth of pore-filling laths and fibrous illites. Analyses of both illite pore-size and crystallite-size distributions indicate that crystal growth occurred by a continuous nucleation and growth mechanism probably controlled by the multiple influx of potassium-rich fluids during late Triassic and Jurassic times. The detailed insight into the textural varieties of illite crystal growth and its calculated permeabilities provides important constraints for understanding the complexities of fluid-flow in tight reservoir sandstones.

多孔砂岩中的成岩伊利石生长导致初始孔隙系统发生显着改变，从而形成致密储层。了解和量化这些变化有助于深入了解储层的孔隙度-渗透率历史，并改进对岩石物理行为的预测。为了表征成岩作用的不同阶段，对来自 Parchim 组 Bebertal 露头的风成砂岩（早二叠世上 Rotliegend 组）进行了聚焦离子束扫描电子显微镜 (FIB-SEM) 研究。基于 3D 显微重建，出现了三种不同纹理类型的伊利石晶体，这在许多致密 Rotliegend 砂岩中很常见，即 (1) 长石颗粒蚀变和相关的伊利石网状结构，(2) 切向颗粒涂层，以及 (3) 孔隙填充板条和纤维。反应织构、孔隙结构量化和流体传输的数值模拟表明，不同世代的纳米孔隙与长石的成岩蚀变和孔隙充填伊利石的自生生长有关。后者导致微观结构的形成，从自生致密的切向晶粒涂层到高度多孔的孔隙填充结构。伊利石的钾长石替代和初始晶粒涂层主要由无序的1组成 后者导致微观结构的形成，从自生致密的切向晶粒涂层到高度多孔的孔隙填充结构。伊利石的钾长石替代和初始晶粒涂层主要由无序的1组成 后者导致微观结构的形成，从自生致密的切向晶粒涂层到高度多孔的孔隙填充结构。伊利石的钾长石替代和初始晶粒涂层主要由无序的1组成M_伊利石，而作为孔隙填充结构出现的外延生长的伊利石板条状和纤维状晶体属于反空 1 M _tv多型。尽管所有分析的 3D 结构都提供了连接的通道，但砂岩渗透率的最大降低发生在最初形成密封蚀变长石的切向伊利石涂层以及随后孔隙填充板条和纤维状伊利石的生长期间。对伊利石孔径和微晶尺寸分布的分析表明，晶体生长是通过连续的成核和生长机制发生的，这可能受三叠纪晚期和侏罗纪时期富钾流体的多次流入控制。对伊利石晶体生长的结构变化及其计算的渗透率的详细了解为理解致密储层砂岩中流体流动的复杂性提供了重要的约束。