Analysis of Sedimentary Environment Conditions for Lacustrine Fine-Grained Sedimentary Rocks and Its Control of Lithofacies Development: A Case Study of the Lower Submember of Member 3 of Shahejie Formation in FY-1 Well, Dongying Sag, Bohai Bay Basin, China

Abstract

In recent years, the studies on fine-grained sedimentation mainly focus on the rock type, sedimentary environment, sedimentation, and sequence stratigraphy, while those on the relationship between sedimentary environment and lithofacies development are rare. However, a clear understanding on the relationship is of great significance to the muddy shale oil and gas exploration. This paper studied the muddy shale of semideep and deep lacustrine facies in the lower submember of Member 3 of Shahejie Formation in FY-1 Well, Dongying Sag, Bohai Bay Basin, East China. Based on geochemical data, the sedimentary environment media conditions and vertical changes of this submember were analyzed by means of core description, thin section authentication, X-ray diffraction (XRD), and other technologies, and the relationship between sedimentary environment and lithofacies development was discussed. The results show that this environment underwent three stages and is featured by cyclicity. From the bottom up, it experienced the semideep, deep, and deep/semideep waters under the relatively dry-cold/relatively warm-wet, warm-wet, and warm-wet/relatively warm-wet paleoclimates, respectively. Correspondingly, the paleoredox transited three stages from reducibility to high reducibility to high reducibility/reducibility; the paleosalinity changed from saline water to brackish water to brackish/saline water. Paleoproductivity was low/relatively high at the beginning, then became high, and finally relatively high. In this submember, the lithofacies primarily includes organic-rich mudstone, organic-rich lime mudstone, organic-rich lime-bearing mudstone, and organic-contained argillaceous limestone/lime mudstone. The sedimentary environment controls the mineral composition and content in the lithofacies and thus determines the lithofacies types. Meanwhile, the cyclicity of environmental change not only leads to that of the lithofacies development but also affects the positions of the lithofacies and its assemblages in sequence stratigraphic framework.

Fine-Grained Lithofacies Types and Sedimentary Model of the Upper Permian Longtan Formation Coal Measures in the Western Guizhou Region, South China

“…Then, the samples were washed with distilled water until neutral and dried at a constant temperature of 60− 80 °C; finally, the samples were combusted in a hightemperature oxygen flow (oxygen purity: 99.9%) to convert the total organic carbon into carbon dioxide, which was then detected by an infrared detector to obtain the total organic carbon content. 51,53 The experiment used a LECO CS-230 carbon-sulfur analyzer, and the test conditions followed the China National Petroleum and Natural Gas Industry Standard GB/T 19145-2003. 2), with yellowish-gray, dark gray, and grayish-black shale; it can be divided into 64 lithostratigraphic layers, including four layers of coal seam, 14 layers of shale, 28 layers of mudstone, and 18 layers of sandstone (Figure 3a−e).…”

“…First, the rock sample is ground into a powder form in an agate mortar with an average particle size of approximately 5 μm or less than 200 mesh. Second, the powdered sample is pressed into a mold and then tested to obtain the mineral mass percentage . The experiment was carried out in the XRD powder crystal laboratory of the Scientific Research Institute of China University of Geosciences (Beijing) using a Japan Rigaku SmartLab (9kw) X-ray diffractometer.…”

“…The dried test samples were ground into particles of approximately 100 mesh in size; then, an excess of dilute hydrochloric acid solution (pure hydrochloric acid/water = 1:7) was used to dissolve the samples under constant temperature conditions of 60–80 °C for more than 2 h to remove the inorganic carbon component in the sample. Then, the samples were washed with distilled water until neutral and dried at a constant temperature of 60–80 °C; finally, the samples were combusted in a high-temperature oxygen flow (oxygen purity: 99.9%) to convert the total organic carbon into carbon dioxide, which was then detected by an infrared detector to obtain the total organic carbon content. , The experiment used a LECO CS-230 carbon-sulfur analyzer, and the test conditions followed the China National Petroleum and Natural Gas Industry Standard GB/T 19145-2003.…”

“…Second, the powdered sample is pressed into a mold and then tested to obtain the mineral mass percentage. 51 The experiment was carried out in the XRD powder crystal laboratory of the Scientific Research Institute of China University of Geosciences (Beijing) using a Japan Rigaku SmartLab (9kw) X-ray diffractometer. The test conditions followed the China National Petroleum and Natural Gas Industry Standard GB/T 19145-2003.…”

Lithofacies Characteristics of Continental Lacustrine Fine-Grained Sedimentary Rocks and Their Coupling Relationship with Sedimentary Environments: Insights from the Shahejie Formation, Dongying Sag

“…It is widely believed that these fine-grained sedimentary rocks are primarily composed of particles smaller than 62.5 µm, including clay minerals, quartz, feldspars, carbonates, and organic matter [2]. Notably, those developed in deep-water environments and rich in organic matter are key source rocks for hydrocarbon generation [3][4][5]. However, due to the small size of mineral particles in fine-grained sedimentary rocks, their susceptibility to weathering, the subtlety of their sedimentary structures, and constraints in experimental conditions, the study of these rocks has long been overlooked [6,7].…”