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Taking the Lower Permian Fengcheng Formation shale in Mahu Sag of Junggar Basin, NW China, as an example, core observation, test analysis, geological analysis and numerical simulation were applied to identify the shale oil micro-migration phenomenon. The hydrocarbon micro-migration in shale oil was quantitatively evaluated and verified by a self-created hydrocarbon expulsion potential method, and the petroleum geological significance of shale oil micro-migration evaluation was determined. Results show that significant micro-migration can be recognized between the organic-rich lamina and organic-poor lamina. The organic-rich lamina has strong hydrocarbon generation ability. The heavy components of hydrocarbon preferentially retained by kerogen swelling or adsorption, while the light components of hydrocarbon were migrated and accumulated to the interbedded felsic or carbonate organic-poor laminae as free oil. About 69% of the Fengcheng Formation shale samples in Well MY1 exhibit hydrocarbon charging phenomenon, while 31% of those exhibit hydrocarbon expulsion phenomenon. The reliability of the micro-migration evaluation results was verified by combining the group components based on the geochromatography effect, two-dimension nuclear magnetic resonance analysis, and the geochemical behavior of inorganic manganese elements in the process of hydrocarbon migration. Micro-migration is a bridge connecting the hydrocarbon accumulation elements in shale formations, which reflects the whole process of shale oil generation, expulsion and accumulation, and controls the content and composition of shale oil. The identification and evaluation of shale oil micro-migration will provide new perspectives for dynamically differential enrichment mechanism of shale oil and establishing a "multi-peak model in oil generation" of shale. [ABSTRACT FROM AUTHOR]

Large shale oil resources were recently been found in lacustrine organic-rich shale with strong heterogeneity, however, few studies have been conducted to examine their oil contents, resulting in considerable risks in lacustrine shale oil exploration. The Middle Permian Lucaogou Formation (P 2 l) shale in Jimusaer Sag is a typical lacustrine deposit with strong heterogeneity, and its shale oil resource shows great potential. Integrated geochemical characterization of 265 core samples were conducted and results show that the P 2 l shale developed in an anoxic lacustrine with stratified salty water and the organic matter in the upper sub-member shale of the P 2 l is more oil-prone than that in the lower sub-member shale of the P 2 l. The hydrocarbon generation potential of the P 2 l shale decreases with the kerogen types changing from Type I to Type III, however, the residual hydrocarbon contents of the P 2 l shale increases from Type I to II 1 kerogen, and then decreases from Type II 1 to III kerogen, this is mainly due to differentiated hydrocarbon expulsion efficiencies among different kerogen types. Based on S 1 and TOC values and the S 1 /TOC ratios, considering the oil enrichment degree, this study classified the shale oil resources in the P 2 l shale into four categories: enriched, moderately enriched, less efficient, and invalid resources. The enriched and moderately enriched resources are mainly shales with Type II 1 kerogen, followed by Type II 2 kerogen, and the middle interval of the Lower P 2 l shale is the most favourable target for further shale oil exploration. The improved evaluation criteria are applicable for evaluating shale oil plays with strong heterogeneity qualitatively and quantitatively in terrestrial lacustrine basins in other parts of the world. [ABSTRACT FROM AUTHOR]

Shale oil exploration of the Permian Lucaogou Formation (P2l) has greatly advanced in the Jimusar Sag in the Junggar Basin. However, despite the strong exploration prospects of shale oil resources, the potential of shale oil resources in the Junggar Basin has been insufficiently assessed. This study performs systematical evaluation of P2l source rocks in the Jimusar Sag and proposes an improved hydrocarbon generation potential method to assess the hydrocarbon generation and expulsion characteristics and evaluates the shale oil resource potential of the P2l source rocks in the Jimusar Sag. The results show that the P2l source rocks are thick (up to 200 m) and are distributed over a wide area (up to 1200 km2) in the study region. It contains high TOC (2%-5%), characterized by dominantly type I and type II kerogen. The source rocks are in the low mature-mature stage, and possess good conditions for generation of hydrocarbons. The P2l source rocks reached the hydrocarbon expulsion threshold at a thermal maturity of 0.8% vitrinite reflectance. The efficiency of hydrocarbon expulsion of the source rock is 34%. The amounts of hydrocarbons generated and expelled were 65 × 108 t. Based on the above information, the shale oil resources potential is calculated to be 43 × 108 t, indicating very good shale oil resource prospect in the P2l source rocks of the Jimusar Sag. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Significant progress has recently been made in tight oil exploration within the Permian Lucaogou (P2l) Formation of the Jimusar Sag. However, current tight oil exploration deployment of the P2l Formation is mainly based on reservoir prediction, which is high risk for tight oil exploration. In this study, the geological and geochemical characteristics of the P2l Formation source rocks, including the distribution, sedimentary environment, organic matter abundance, kerogen types and thermal maturity were investigated. Hydrocarbon generation and expulsion intensity were evaluated through an improved hydrocarbon generation potential methodology, and the significance of source rocks in tight oil source and occurrence was systematically investigated. Results indicate that P2l Formation source rocks with total organic carbon >1.0 wt% occur widely (an area up to 1500 km2), are thick (up to 160 m), were deposited in a lacustrine weakly reducing sedimentary environment with relatively low salinity, have a high total organic content with a mean value of 3.12 wt%, are dominated by type II kerogen and have reached the early mature to mature stage. Modelling results indicate that the source rocks reached the hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.48% and 0.86% vitrinite reflectance, respectively. The comprehensive hydrocarbon expulsion efficiency was approximately 30%, and the maxima of hydrocarbon generation and expulsion intensities for P2l Formation source rocks are 1200 × 104 and 425 × 104 t/km2. The tight oil is sourced from adjacent source rocks that are interbedded with, or are close to, the reservoirs. The migration of oil generated from the source rocks occurs over very short distances. The oil filling degree index (oil bearing thickness/P2l Formation thickness) is higher at a closer proximity to the source rocks, and where it is higher the hydrocarbon generation intensity of the source rocks is also elevated. In addition, the greater the hydrocarbon expulsion intensity of the source rocks, the higher the daily oil production values (ton/day) from prospect wells. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The petroliferous Permian system of the Junggar Basin in northwest China is predominantly a conventional oil exploration region. To assist in the unconventional tight oil reservoir exploration, the hydrocarbon expulsion potential of source rocks and its influence on the tight oil distribution of the Middle Permian Lucaogou Formation (P 2 l) in the Jimsar Sag are discussed. The researches are based on geological and geochemical characteristics such as the distribution, abundance, type, thermal maturity of source rocks, and “sweet spots”. Meanwhile, hydrocarbon expulsion intensity and quantity were evaluated with hydrocarbon generation potential method. The Middle Permian Lucaogou source rocks have wide distribution and high thickness (mostly thicker than 100 m). The source rocks exhibit low to high TOC (mainly ranges from 1.0 wt% to 5.0 wt%) and primarily contain type-II kerogen, resulting in significant hydrocarbon expulsion potential under moderate mature thermal evolution (R o mainly ranges from 0.55% to 1.05%). According to the hydrocarbon expulsion modelling, the source rocks reached the hydrocarbon expulsion threshold at 0.73% R o and the hydrocarbon expulsion rate became greatest at 0.9% R o . The comprehensive hydrocarbon expulsion efficiency was approximately 48%. About 18.7×10 8 t of hydrocarbons were expulsed from the Lucaogou source rocks in the Jimsar Sag. The hydrocarbon expulsion intensities are relatively large and rang from 150×10 4 t/km 2 to 400×10 4 t/km 2 in the center and west area of the Sag, where is the superimposed area of source rock thicker than 200 m, TOC greater than 3.5% and R o higher than 0.85% in the sag. There are 17 exploratory wells obtaining commercial oil flow in the Sag. 16 of the 17 exploratory wells are located in the area with hydrocarbon expulsion intensity greater than 50×10 4 t/km 2 . By contrast, other exploratory wells outside the hydrocarbon expulsion coverage area have slight show of oil, even dry. In addition, there is positive correlation between the hydrocarbon expulsion intensity and the daily output of well testing. It is concluded that the tight oil exploration should focus on the area with hydrocarbon expulsion intensity greater than 100×10 4 t/km 2 , which is a favorable area for commercial hydrocarbon accumulation and exploration. [ABSTRACT FROM AUTHOR]

Combined with the actual geological settings, tight oil is the oil that occurs in shale or tight reservoirs, which has permeability less than 1 mD and is interbedded with or close to shale, including tight dolomitic oil and shale oil. The Fengcheng area (FA), at the northwest margin of the Junggar Basin, northwest China, has made significant progress in the tight oil exploration of the Fengcheng (P1f) Formation recently, which indicates that the tight oil resources have good exploration prospects. Whereas the lack of recognition of hydrocarbon generation and expulsion characteristics of Permian P1f source rocks results in the misunderstanding of tight oil resource potential. Based on the comprehensive analysis of geological and geochemical characteristics of wells, seismic inversion, sedimentary facies, tectonic burial depth, etc., the characteristics of P1f source rocks were investigated, and the horizontal distributions of the following aspects were predicted: the thickness of source rocks, abundance and type of organic matter. And on this basis, an improved hydrocarbon generation potential methodology together with basin simulation techniques was applied to unravel the petroleum generation and expulsion characteristics of P1f source rocks in FA. Results show that the P1f source rocks distribute widely (up to 2039 km2), are thick (up to 260 m), have high total organic content (TOC, ranging from 0.15 to 4 wt%), are dominated by type II kerogen and have entered into low mature-mature stage. The modeling results indicate that the source rocks reached hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.5% Ro and 0.85% Ro and the comprehensive hydrocarbon expulsion efficiency was about 46%. The amount of generation and expulsion from the P1f source rocks was 31.85 × 108 and 15.31 × 108 t, respectively, with a residual amount of 16.54 × 108 t within the source rocks. Volumetrically, the geological resource of shale oil is up to 15.65 × 108 t. Small differences between the amounts calculated by the volumetric method compared with that by hydrocarbon generation potential methodology may be due to other oil accumulations present within interbedded sands associated with the oil shales. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Jurassic strata along the southern margin of Junggar Basin are important petroleum system elements for exploration in northwest China. The Lower and Middle Jurassic source rock effectiveness has been questioned as exploration progresses deeper into the basin. These source rocks are very thick and are distributed widely. They contain a high total organic carbon composed predominantly of Type III kerogen, with some Type II kerogen. Our evaluation of source rock petroleum generation characteristics and expulsion history, including one-dimensional basin modeling, indicates that Jurassic source rocks are gas prone at deeper depths. They reached peak oil generation during the Early Cretaceous and began to generate gas in the Late Cretaceous. Gas generation peaked in the Paleogene-Neogene. Source rock shales and coals reached petroleum expulsion thresholds at thermal maturities of 0.8% and 0.75% vitrinite reflectance, respectively, when the petroleum expulsion efficiency was ∼40%. The petroleum generated and expelled from these source rocks are 3788.75 × 108 and 1507.55 × 108 t, respectively, with a residual 2281.20 × 108 t retained in the source rocks. In these tight reservoirs, a favorable stratigraphic relationship (where tight sandstone reservoirs directly overlie the source rocks) indicates short vertical and horizontal migration distances. This indicates the potential for a large, continuous, tight-sand gas resource in the Lower and Middle Jurassic strata. The in-place natural gas resources in the Jurassic reservoirs are up to 5.68 × 1012 − 15.14 × 1012 m3. Jurassic Badaowan and Xishanyao coals have geological characteristics that are favorable for coal-bed methane resources, which have an in-place resource potential between 3.60 × 1012 and 11.67 × 1012 m3. These Lower and Middle Jurassic strata have good shale gas potential compared with active US shale gas, and the inferred in-place shale gas resources in Junggar Basin are between 20.73 × 1012 and 113.89 × 1012 m3. This rich inferred conventional and unconventional petroleum resource in tight-sand, coal-bed, and shale gas reservoirs makes the deeper Jurassic strata along the southern margin of Junggar Basin a prospective target for future exploration. [ABSTRACT FROM AUTHOR]

New oil reservoirs have been discovered recently in the Jurassic Toutunhe Formation in the Fudong slope, Junggar basin in China. The process and mechanism of lateral petroleum migration in the Jurassic System in the Fudong slope was investigated based on the geological analysis of the strata, porosity and permeability of the reservoir rocks and geochemistry on oil-source correlation and oil-oil correlation. The results indicate that hydrocarbons of the Toutunhe Formation were primarily derived from the Middle-Lower Jurassic and Middle Permian source rocks of the western Fukang Depression and migrated along the axis from west to east. The thickness, sand/strata ratio, porosity and permeability of the Toutunhe 2 member are all better than that of the Toutunhe 1 member, making it the main carrier bed of the hydrocarbons lateral migration. [ABSTRACT FROM AUTHOR]