The Ordovician and Silurian deposits in the Baltic Basin are represented by siltstones, mudstones, limestones, marls, sandstones and, most commonly, claystones with a markedly shaley structure. Claystones that are particularly rich in organic matter are considered as potential reservoirs for shale gas accumulations. Samples from 11 boreholes, including core samples of the Piaśnica, Słuchowo, Kopalino, Sasino, Prabuty, Jantar, Pelplin and locally Pasłęk, Kociewie and Puck formations, were analysed by optical microscopy, cathodoluminescence (CL), scanning electron microscopy (SEM) and energy-dispersive spectrometry and X-ray diffraction analyses (XRD). The Piaśnica, Sasino, Jantar, Pasłęk and Pelplin formations are characterized locally by a dominance of black bituminous claystones with a high content of organic matter, and a generally consistent clay mineral composition. Individual samples only show variations in silt fraction and carbonate content. Very important is the negligible proportion of swelling minerals in the clay fraction; the percentage of smectite in the mixed-layered illite/smectite minerals does not exceed 15%. It is important for the rocks to have adequate [SiO2 >10%; Quartz (Q) + Feldspars (Fs) + Carbonates >40%] brittleness. The content of quartz, feldspars and carbonates (here >40%) suggests that the claystones are susceptible to hydraulic fracturing. The claystones show micropores between detrital grains, between the flakes of clay minerals, within pyrite framboids, and organic matter and secondary micropores within grains.

波罗的海盆地的奥陶系和志留系沉积物以粉砂岩、泥岩、石灰岩、泥灰岩、砂岩和最常见的具有明显页岩结构的粘土岩为代表。有机质含量特别丰富的粘土岩被认为是页岩气聚集的潜在储层。来自 11 个钻孔的样品，包括 Piaśnica、Słuchowo、Kopalino、Sasino、Prabuty、Jantar、Pelplin 和当地的 Pasłęk、Kociewie 和 Puck 地层的岩心样品，通过光学显微镜、阴极发光 (CL)、扫描电子显微镜 (SEM) 和能量色散光谱法和 X 射线衍射分析 (XRD)。Piaśnica、Sasino、Jantar、Pasłęk 和 Pelplin 地层的特征是当地以富含有机质的黑色沥青粘土岩为主，和大体一致的粘土矿物成分。个别样品仅显示淤泥分数和碳酸盐含量的变化。非常重要的是粘土部分中溶胀矿物的比例可以忽略不计；混合层状伊利石/蒙脱石矿物中蒙脱石的百分比不超过15%。对于岩石来说，重要的是要有足够的 [SiO2 >10%；石英 (Q) + 长石 (Fs) + 碳酸盐 >40%] 脆性。石英、长石和碳酸盐的含量（此处 >40%）表明粘土岩易受水力压裂的影响。粘土岩在碎屑颗粒之间、粘土矿物薄片之间、黄铁矿小块内以及颗粒内的有机质和次生微孔中显示出微孔。非常重要的是粘土部分中溶胀矿物的比例可以忽略不计；混合层状伊利石/蒙脱石矿物中蒙脱石的百分比不超过15%。对于岩石来说，重要的是要有足够的 [SiO2 >10%；石英 (Q) + 长石 (Fs) + 碳酸盐 >40%] 脆性。石英、长石和碳酸盐的含量（此处 >40%）表明粘土岩易受水力压裂的影响。粘土岩在碎屑颗粒之间、粘土矿物薄片之间、黄铁矿小块内以及颗粒内的有机质和次生微孔中显示出微孔。非常重要的是粘土部分中溶胀矿物的比例可以忽略不计；混合层状伊利石/蒙脱石矿物中蒙脱石的百分比不超过15%。对于岩石来说，重要的是要有足够的 [SiO2 >10%；石英 (Q) + 长石 (Fs) + 碳酸盐 >40%] 脆性。石英、长石和碳酸盐的含量（此处 >40%）表明粘土岩易受水力压裂的影响。粘土岩在碎屑颗粒之间、粘土矿物薄片之间、黄铁矿小块内以及颗粒内的有机质和次生微孔中显示出微孔。石英 (Q) + 长石 (Fs) + 碳酸盐 >40%] 脆性。石英、长石和碳酸盐的含量（此处 >40%）表明粘土岩易受水力压裂的影响。粘土岩在碎屑颗粒之间、粘土矿物薄片之间、黄铁矿小块内以及颗粒内的有机质和次生微孔中显示出微孔。石英 (Q) + 长石 (Fs) + 碳酸盐 >40%] 脆性。石英、长石和碳酸盐的含量（此处 >40%）表明粘土岩易受水力压裂的影响。粘土岩在碎屑颗粒之间、粘土矿物薄片之间、黄铁矿小块内以及颗粒内的有机质和次生微孔中显示出微孔。