The shale oil resources of the Permian Fengcheng Formation in the Mahu Sag are abundant, and the types of shale oil reservoirs therein are diverse. However, differences in the reservoir spaces, occurrence states, and source–reservoir configurations of different types of shale oil reservoirs restrict the in-depth understanding of the enrichment and accumulation mechanisms of shale oil in this formation. Thus, using multiple complementary experiments, this study systematically compared laminated-type and sandwich-type shale oil reservoirs (LTSOR and STSOR), in terms of hydrocarbon generation potential, physical characteristics, and oil-bearing properties. These two types of shale oil reservoirs had distinct differences in total organic carbon (TOC), porosity, oil saturation index, and S1, demonstrating differences in accumulation mechanisms. These two types of reservoirs were mainly dominated by inorganic intergranular pores and dissolution pores, and the storage capability of STSOR was much better than that of LTSOR. Specifically, STSOR mainly developed macropores, whereas LTSOR developed macropores and mesopores. The free oil content in the STSOR was found to be higher than that of the adsorbed oil, whereas the free and adsorbed oil contents in the LTSOR were similar. Furthermore, the shale oil occurrence in the STSOR was mainly affected by pore structure and mineral composition, whereas the shale oil occurrence in the LTSOR was affected by pore structure, mineral composition, TOC content, and sedimentary structure. The source–reservoir configuration relationship of STSOR was one where the upper and lower shale layers were source rocks, whereas the intercalated siltstone layers were reservoirs. The source–reservoir configuration of the LTSOR involved bright laminae as reservoirs and dark laminae as source rocks (i.e., integrated source and reservoir). Hydrocarbon accumulation models were established for the STSOR and LTSOR that involved source–reservoir configurations, occurrence states, and migration directions. 

Occurrence Mechanisms of Laminated-Type and Sandwich-Type Shale Oil in the Fengcheng Formation of Mahu Sag, Junggar Basin

Alkaline lacustrine deposits are known for their high primary productivity, unique aquatic environments, and sedimentary patterns, which are conducive to the formation and preservation of organic matter. Consequently, related source rocks have significant hydrocarbon generation potential. The study of hydrocarbon source rocks in the Fengcheng Formation of the Mahu Sag in the Junggar Basin serves as a good example for understanding organic matter enrichment and hydrocarbon generation characteristics of such alkaline lacustrine deposits source rocks. However, the characteristics of organic matter and hydrocarbon generation model in the source rocks of Fengcheng Formation lack systematic research, thus hindering exploration planning and favorable area selection. In this study, analysis of mineral content based on X-ray diffraction and organic geochemical analysis were employed, along with systematic observations of bio-precursor types under fluorescence microscopy. Based on mineral identification and quantitative statistics, the Fengcheng Formation was classified into three zones according to different alkaline mineral assemblages: an inner zone dominated by sodium carbonate minerals, a transitional zone with higher borosilicate mineral content, and a marginal zone characterized by abundant calcite deposition. The inner zone is characterized by the presence of lamalginite and telalginite, which are influenced by high pH values and changes in water depth, and exhibit high maturity characteristics. The transitional zone exhibits high total organic carbon (TOC) values, with predominantly type I and type II1 kerogen. Under fluorescence, the main components were observed to be lamalginite and telalginite, with their distribution being influenced by high salinity and ash supply. The marginal zone has relatively lower TOC than the previous two zones, which is dominated by type II2 kerogens, and contains a certain quantity of terrigenous inertinite supply. The hydrocarbon generation patterns of lamalginite and telalginite are consistent with the bimodal efficient hydrocarbon generation model observed in the source rocks of Fengcheng Formation, revealing the unique hydrocarbon generation model of organic matter in alkaline lacustrine source rocks. This research has significant implications for the exploration strategy of the alkaline lacustrine deposits in the Fengcheng Formation and similar oil- and gas-bearing basins.

/pdf/distribution-characteristics-of-organic-matter-in-the-2i8eibk1.pdf

Distribution characteristics of organic matter in the Fengcheng Formation in Mahu Sag, Junggar Basin: implications for hydrocarbon generation model in alkaline lacustrine deposition

Controlling Factors of Shale Oil Enrichment in the Paleogene Funing Formation, Gaoyou Sag, Subei Basin, China

Abstract Lake-phase organic-rich shales are widely developed in the fifth member (Xu5 Member) of the Triassic Xujiahe Formation in the Sichuan Basin. However, due to the lack of understanding of the paleoclimate and paleoenvironment, the mechanism of organic matter enrichment in the Xu5 Member shale is controversial. To address these issues, this study takes the X5 Member in the Tianfu area as a case study. By analyzing its paleoenvironmental characteristics and correlating with organic matter development, we elucidate the influence of paleoenvironmental conditions on organic matter enrichment patterns in X5 shale. The results show that: (1) the shale of the Xu5 Member has high total organic carbon content and the organic matter type is dominated by type III, which has good potential for anger. (2) Chemical index of alteration (CIA)–weathering index of Parker (WIP) cross-plots indicate first-cycle deposition of the Xu5 Member shales with significant terrigenous input. La/Th, Hf, and Al 2 O 3 /TiO 2 ratios collectively suggest relatively slow sedimentation rates. Provenance analysis reveals dominant felsic igneous sources with minor mafic contributions. C -values and Sr/Cu ratios consistently indicate semi-humid to humid paleoclimatic conditions during deposition. Sr/Ba (&lt;0.5) and Al 2 O 3 /MgO (&gt;7) ratios constrain paleosalinity to freshwater-brackish conditions. Redox proxies (Ni/Co, U/Th, V/Cr, U EF , Mo EF ) uniformly demonstrate oxygenated bottom-water conditions. Productivity indicators (P/Ti, Cu/Ti, Ba bio ) reveal elevated paleoproductivity in early Xu5 3 to Xu5 2 , with lower values in overlying intervals. (3) The organic matter enrichment of the shale in the Xu5 Member is mainly affected by the redox conditions of the bottom water, paleoproductivity, and paleosalinity, and the more reducing the bottom water is, the higher the paleoproductivity and the higher the paleosalinity are, the more favorable the organic matter enrichment is. In addition, in the sub-member of Xu5 1 and Xu5 2 , paleoclimate, land-source input, and sedimentation rate are also secondary factors affecting the degree of organic matter enrichment. 

pdf/paleoenvironmental-characteristics-of-continental-shale-and-yuochfknpau0.pdf

Paleoenvironmental characteristics of continental shale and its significance to organic matter enrichment: Taking the fifth member of Xujiahe Formation in Tianfu area of Sichuan Basin as an example

Transgressive Lacustrine Shale Sedimentary Environment, Enrichment Model and Mechanisms for Organic Matter in the Paleocene Funing Formation, China

Organic matter in depositional environment is the essential material for oil and gas generation. Total organic carbon (TOC) is one of the important parameters for estimating the hydrocarbon generation potential of shale oil and predicting sweet spots. The TOC of the second member of the Funing Formation (Ef2) ranges from 0.25% to 2.30%. TOC is higher in the upper shale and lower in the lower shale of the Funing Formation, showing a significant enrichment difference. However, there have been few reports on the study of the main controlling factors for the differential enrichment of organic matter in Ef2. This study aims to reconstruct the paleoenvironment of lacustrine shale in Ef2. Additionally, this study aims to clarify the influence of the paleoenvironment on the differential enrichment of organic matter in Ef2. For this purpose, systematic mineralogical and geochemical analyses were conducted on 72 samples from a representative well. The results indicate that, based on parameters such as paleoclimate (chemical index of alteration, CIA), paleosalinity (Sr/Ba), paleoredox conditions (Cu/Zn), paleoproductivity (P/Ti), water depth (Rb/K), and terrigenous clastic input (Al, Ti), the paleoenvironment during the deposition of the Ef2 shale clearly exhibited significant changes. During the early stage, the climate was hot and dry, with shallow water, weak chemical weathering, low productivity, and salinity ranging from saline to brackish. In the later stage, the climate became warm and humid, with deeper water, moderate chemical weathering, high productivity, and salinity ranging from brackish to freshwater. There are significant errors in directly using the Sr/Ba index to evaluate the paleosalinity of Ef2 shale. Carbonate minerals and calcium-rich bioclasts may increase the Sr/Ba ratio, and the corrected Sr element content is only 44.29% of the original sample. The enrichment of organic matter is clearly controlled by productivity levels and climatic conditions. The higher the paleoproductivity and the warmer and more humid the climate, the more enriched the organic matter becomes. Fundamental differences in paleoproductivity govern the enrichment of organic matter during the deposition process of the Ef2 shale. The organic matter enrichment pattern in the Ef2 shale represents a typical productivity model.

Paleoenvironmental Characteristics of Lacustrine Shale and Its Impact on Organic Matter Enrichment in Funing Formation of Subei Basin

<jats:p>Due to an increasing energy demand and the depletion of conventional oil, there is ever increasing demand for unconventional shale oil and gas resources. As the most hydrocarbon-rich sag in the Junggar Basin, the development prospects for shale oil in the Mahu Sag have become a focus of research. However, so far, there have been few studies of the oil-bearing properties of shale and shale oil mobility in the sag. This paper redresses this using a range of methods, such as pyrolysis and multi-temperature step pyrolysis. The results show that the Fengcheng Formation shales are generally good quality source rocks. The main body of the shale is low mature-mature, and the type of organic matter is mostly Type II kerogen. In the depth intervals at 4616.45~4640.30 m, 4661.25~4695.20 m, 4728.30~4759.80 m, 4787.60~4812.30 m, and 4876.70~4940.25 m, the oil-bearing properties of the shale and shale oil mobility are good, with an average <jats:inline-formula>
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                     </math>
                  </jats:inline-formula> of more than 1.5 mg/g, OSI of more than 100 mg/g.TOC-1, a ratio of free/adsorbed oil (<jats:inline-formula>
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                  </jats:inline-formula>) of more than 3, and a ratio of free/total oil (<jats:inline-formula>
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                              <msub>
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                  </jats:inline-formula>) of more than 80%. The second member (P1f2) and the lower part of the first member (P1f1) of the formation offer the most promising commercial prospects. Shale oil mobility in the formation is greatly affected by the abundance of organic matter. The higher the <jats:inline-formula>
                     <math xmlns="http://www.w3.org/1998/Math/MathML" id="M4">
                        <mtext>TOC</mtext>
                     </math>
                  </jats:inline-formula> value, the greater the hydrocarbon generation capacity, and the better its adsorption capability in the shale. The Fengcheng Formation shale is mature, and shale oil mobility is good. Impacted by the main reservoir space, the felsic shale in the formation has optimal shale oil mobility, with the shale oil being characterized by self-generation and self-storage, and accumulation in adjacent layers.</jats:p>

/pdf/evaluation-of-the-oil-bearing-properties-of-shale-and-shale-269eacfp.pdf

Evaluation of the Oil-Bearing Properties of Shale and Shale Oil Mobility in the Fengcheng Formation in the Mahu Sag, Junggar Basin, Northwest China: A Case Study of Well Maye-1

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Paleoenvironmental Characteristics of Lacustrine Shale and Its Impact on Organic Matter Enrichment in Funing Formation of Subei Basin

Evaluation of the Oil-Bearing Properties of Shale and Shale Oil Mobility in the Fengcheng Formation in the Mahu Sag, Junggar Basin, Northwest China: A Case Study of Well Maye-1