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 S 1 of more than 1.5 mg/g, OSI of more than 100 mg/g.TOC-1, a ratio of free/adsorbed oil ( S 1 − 1 + S 1 − 2 / S 2 − 1 ) of more than 3, and a ratio of free/total oil ( S 1 − 1 + S 1 − 2 / S 1 − 1 + S 1 − 2 + S 2 − 1 ) 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 TOC 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.
The enrichment mechanism and process of shale oil are key issues in the studies on shale oil. To date, a variety of methods have been applied to describe the characteristics of typical shale oil reservoirs and reveal the potential influencing factors on marine and freshwater continental shale. However, geological characteristics and influencing mechanism of saline lake shale oil reservoirs remain poorly understood.Here, we report our investigation on the petrological, organic geochemical, and pore structure characteristics of the 10th cyclothem of the third member (Eq3 4 10) of the saline lake-formed Qianjiang Formation in Jianghan Basin using X-ray fluorescence spectroscopy, X-ray diffraction, field emission scanning electron microscopy, lowtemperature nitrogen adsorption, and high-pressure mercury intrusion. The shales of Eq3 4 10 contain high average carbonate contents (45.53%) and clay minerals (20.89%), as well as anisometric glauberite, quartz, feldspar, rock salt, and pyrite. The main lithofacies are dolomitic mudstone, argillaceous dolomite, and calcareous mudstone. The shale samples tested yield total organic carbon (TOC) and S 1 + S 2 values of 1.94 wt% and 10.46 mg HC/g rock, respectively, and are primarily types II 1 and II 2 kerogen with thermal maturities between 0.5 and 1.0%. The abundance of organic matter in calcareous mudstone and dolomitic mudstone facies of the Eq3 4 10 shales was relatively high. Inorganic pores are the dominant pore types, including intercrystalline pores within the carbonate and clay minerals, while mesopores and macropores contribute most to the pore volume. Better pore structures exist in argillaceous dolomite and dolomitic mudstone facies, and their characteristics are mainly affected by the compositions of dolomite, clay minerals, and glauberite and, thus, the TOC and oil contents of the shale oil reservoir.
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