Evaluation of the Shale Oil Reservoir and the Oil Enrichment Model for the First Member of the Lucaogou Formation, Western Jimusaer Depression, Junggar Basin, NW China

Abstract

The Lucaogou Formation (Fm) in the Jimusaer depression is the first large-scale development of a terrigenous clastic sedimentary shale oil reservoir in China. Nearly one billion tons of shale oil resources have been discovered. However, the current exploration and development is concentrated in the eastern part of the sag. The limited geological understanding in the western area has restricted the prediction and development of “sweet spots” for shale oil. To help rectify this, we have studied the petrology, geochemistry, oil content, and pore properties of the second part of the first member (Mbr) of the Lucaogou Fm (P 2 l 1 2 ) in a typical well (Ji-X) in the western part of the sag. The results show that P 2 l 1 2 in the Jimusaer sag is a mixed fine-grained sedimentary system composed of sandstone, mudstone, and carbonate, which can be divided into seven types: dolomitic mudstone, calcareous mudstone, mudstone, mixed fine-grained rock, argillaceous limestone, sandstone, and argillaceous dolomite. The organic matter type of P 2 l 1 2 in well Ji-X is dominated by types I and II, and this is the best source rock in the whole exploration area of the Jimusaer sag. The overall oil saturation is relatively high, but the maturity of crude oil is low, and the overall oil quality is heavy, which is mainly controlled by the sedimentary environment and maturity of source rocks. Lithology and reservoir physical properties are the key to control oil content. The high-quality light oil reservoir lithology is argillaceous dolomite and sandstone. The higher the content of macropores and mesopores, the weaker the heterogeneity of the pore structure, and the better the oil content in the reservoir. There are four light oil sweet spots in the upper part (burial depth less than 4366 m), and there are excellent source rocks with high HI and high organic matter content near each sweet spot. This discovery of shale oil enrichment regularity will effectively guide the development of shale oil in continental lacustrine basins in other parts of the world.

Novel Insights into the Influence of Soil Microstructure Characteristics on the Migration and Residue of Light Non-Aqueous Phase Liquid

“…Most of the soil pore size of Jiangsu paddy soil, Jiangxi red earth, Hunan red earth, and Guizhou yellow soil was lower than 7.5 μm, and the pore volumes were 0.0243, 0.052, 0.0462, and 0.0317 cm 3 /g, respectively. This phenomenon was due to the fine-grained soils with high content that could easily enter the interior of the mesopores, which reduced the connectivity of soil pores and formed fine pores [ 36 ].…”

Oil Retention in Shales: A Review of the Mechanism, Controls and Assessment

“…Chen G. H. et al (2018) reported that 80% of shale oil is distributed in macropores. In fact, with increasing pore size, pore volume and porosity, the oil content in shales usually increases (Wang et al, 2019b;Song et al, 2020;Wang B. Y. et al, 2021). Because the density of the generated oil and gas is lighter than that of kerogen, the volume expansion and the overpressure phenomenon occurs in shales, resulting in the generation of oil expulsion fractures (Sun L. D. et al, 2021).…”

“…In recent years, an increasing number of studies on shales has been performed on their evolution of hydrocarbon generation, retention and expulsion (Shao et al, 2020;Song et al, 2021a;Sun J. et al, 2021;Hou et al, 2021b;Song et al, 2021b;Stockhausen et al, 2021), oil retention mechanism (Ritter, 2003;Tian et al, 2014;Li et al, 2016;Qiu et al, 2016;Han et al, 2017;Tian et al, 2017;Hou et al, 2020), influencing factors of shale oil enrichment (Han et al, 2015;Zou et al, 2019a;Sun et al, 2019;Chen et al, 2020;Milliken et al, 2021) and geological evaluation (Lu et al, 2012;Kumar et al, 2017;Hu et al, 2018;Qian et al, 2018;Wang et al, 2019b;Li J. B. et al, 2020b;Wang B. Y. et al, 2021). Literatures on shale oil are increasing year by year, shale oil has become a hot topic, and Chinese scholars have carried out much shale oil research work and achieved outstanding contributions (Figure 1).…”

Oil Mobility Evaluation of Fine-Grained Sedimentary Rocks with High Heterogeneity: A Case Study of the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China

“…The phenomenon is known as the “oil crossover effect”, and the higher the OSI is, the more content of movable oil will be. However, when the pyrolysis S 1 and TOC values are low, the OSI may also have a high value . Therefore, it is necessary to combine the hydrogen index (HI), production index (PI), and other parameters to determine the optimal oil effective flow point. , Second, recent studies have shown that shale oil cannot be released completely before 300 °C. , Therefore, S 1 is not entirely free oil, and S 2 does not completely represent the kerogen hydrocarbon generation potential .…”