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Organic matter (OM) pores are crucial to porosity in many shale gas reservoirs, but the origin and types of OM pores remain controversial. In this paper, the OM types are systematically identified and analyzed in the Wufeng−Longmaxi Formations from wells JY 1 and JY 2 in the Jiaoshiba gas field, Sichuan Basin. The results indicate that the OM comprises several hydrocarbon-generating organisms, such as various algae (multi-and unicellular algae, colonial algae, acritarch, etc.), graptolite, sponge spicule, and other fossil fragments, as well as several amorphous OM types, such as solid bitumen and strongly compacted algae. The OM pores have inherited the morphology and structure of multicellular algae and are commonly hundreds of nanometers, some of which even reach micrometer size, exhibiting irregular, bubble-like, spherical, and/or elliptical shapes. In the unicellular algae, only a small amount of OM pores are observed, which are isolated and distributed randomly. The OM pores, either irregular or oval, are tens to more than 100 nm, which are developed by the arrangement gap between the unicellular algae, and some are generated inside the unicellular algae by hydrocarbon generation and expulsion. Two types of OM pores developed in solid bitumen, including bitumen−spherulite pores and vesicular pores. The bitumen−spherulite pores are formed by the arrangement of nanoscale bitumen−spherulite with a pore diameter of nanometer scale. The vesicular pores are formed by gas generation and expulsion after oil cracking, and the shape is mostly sporadic, isolated with various sizes ranging from 500 nm to 3 μm. The OM pores in graptolite, sponge spicule, radiolarian, and other fossil fragments are much fewer in quantity and smaller in size. The OM pores may have only developed on the surface of graptolite. The pores are commonly developed in the walls of the fossil fragments and in the solid bitumen by filling in the biological cavity of the sponge spicule. Therefore, it is concluded that the OM types are the pivotal causes of different OM pore types and properties. Multicellular algae are most beneficial to OM pore development, serving as the major producer of OM pores. In the profile of the Wufeng−Longmaxi shales, the vertical variation of OM types and OM pores are diverse in different graptolitic zones. The dominant hydrocarbon-generating organisms in the WF2−LM4 graptolitic zone are multicellular algae and graptolite, followed by a small number of unicellular algae, sponge spicule, radiolarian, and other fossil fragments. The OM pores are mainly developed in multicellular algae and graptolite, with only a few developed in solid bitumen and unicellular algae. In the LM5− LM8 graptolitic zone, however, the hydrocarbon-generating organisms are primarily unicellular algae, with little multicellular algae, graptolite, sponge spicule, and other fossil fragments. The OM pores are mainly developed in unicellular algae and solid bitumen. The new findings provide evidence to support the proposal that multicellular algae are th...

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The trapped electron modes (TEMs) are numerically investigated in toroidal magnetized hydrogen, deuterium and tritium plasmas, taking into account the effects of impurity ions such as carbon, oxygen, helium, tungsten and others with positive and negative density gradients with the rigorous integral eigenmode equation. The effects of impurity ions on TEMs are investigated in detail. It is shown that impurity ions have substantially-destabilizing (stabilizing) effects on TEMs in isotope plasmas for(< 0), opposite to the case of ion temperature gradient (ITG) driven modes. Detailed analyses of the isotope mass dependence for TEM turbulences in hydrogenic isotope plasmas with and without impurities are performed. The relations between the maximum growth rate of the TEMs with respect to the poloidal wave number and the ion mass number are given in the presence of the impurity ions. The results demonstrate that the maximum growth rates scale as γ ∝ − M i max 0.5 in pure

The linear behaviors of the double tearing mode (DTM) mediated by parallel electron viscosity in cylindrical plasmas with reversed magnetic shear and thus two resonant rational flux surfaces is numerically investigated. The distance between the two surfaces is found to play an important role for modes with poloidal mode number m&gt;1. Two modes, one of which is centered at the inner rational surface and the other is located between the two surfaces, are simultaneously unstable and the growth rates show the standard single tearing mode (STM) scaling as γ∝R−1/3 when the distance is large (here, the Reynolds number R≡τυ/τh, τυ, and τh are, respectively, the viscosity penetration time of the magnetic field and the Alfvén time for a plasma sheet of width a). The latter is unstable only and the growth rate transits to the standard DTM scaling as γ∝R−1/5 for low-m (e.g., m&lt;4) modes and keeps the STM scaling γ∝R−1/3 for high-m (e.g., m∼10) modes, which are found dominant, when the distance is decreased. In contrast, two unstable modes extending from plasma center to the two rational surfaces, respectively, coexist and the growth rates always show the scaling of γ∝R−1/5, independent of the distance, when the poloidal mode number m=1. The DTMs mediated by electron viscosity are enhanced by plasma resistivity of the range where the growth rate of the mode induced by the latter alone is comparable with that mediated by the former alone and vice versa. Otherwise, the growth rate of the mode is equal to the higher of the modes mediated by resistivity or electron viscosity alone when both of them are taken into account.

Qiangtang Basin is an important exploration target in Tibetan area that was conducted little exploration and research before this study. Xiaochaka Formation is major source rocks in Upper Triassic, Mesozoic in the basin. According to the evaluation standard of source rocks established specially in this basin, the occurrence features of this formation in different structural units was analyzed comprehensively and then the favorable source kitchens were predicted on the aspects of its sedimentary environment, thickness and organic geochemical characteristics. The work was conducted on the samples from many geological profiles in field survey routes and the analytical data on organic carbon, maceral, rock pyrolysis, vitrinite and bitumen reflectance, and carbon isotopes, etc. The conclusions are as follows: firstly, the organic matter abundance of limestone and mudstone in Xiaochaka Formation is high so that they belong to medium-good source rocks; however, the actual areal division of their distribution shows by the fact that the values are variable in different areas; this formation mainly distributes in the middle part of Southern Qiangtang Basin with mainly II B organic matter type and high maturity; limestone is slightly better than mudstone in organic matter type, but smaller in the favorable source kitchens. All the above-mentioned research has an important reference meaning for the further determination of major source rocks, resource evaluation and exploration prospect on oil and gas.

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