SUPERMICRO SPHERICAL OBJECTS IN TIGHT RESERVOIRS—A POSSIBLE HYDROCARBON GENERATION MATERIAL FOUND IN JUNGGAR BASIN, NW CHINA

Junggar Basin is located in northern Xinjiang, China. It was an intracontinental faulted-rift basin during late Carboniferous to mid-Permian. Ultrabasic, acid volcanic rocks and carbonate rocks are dominant lithofacies. The mixed deep alkaline magma and hydrothermal fluids during deposit made a special set of magmatic-hydrothermal sedimentary rocks. Lucaogou Formationof Permian (lower Guadalupian) developed tight reservoirs which mainly consist of laminated alkali-parlkaline intermediate tuffs (andesite) and ultra-basic tuffs (carbonate rocks). Features of geochemistry show that they were mantle derived ^[1-3].

Some special supermicro spherical on the surface of minerals were observed within high oil potential intervals via scanning electron microscope. The supermicro spherical objects show two shapes. The first type is uniform spheres with diameter of 0.1 μm. The second one combined of multiple spheres, such as one or two spheres with a big sphere, or four or six spheres with a big one. Big spheres are 1-6 μm in size, whereas small ones are 0.1-0.5μm. Abundant oil drops occur around those spheres and show black concentric circle or in disseminated shapes. Minerals adhered by the supermicro spherical objects are mainly calcite, dolomite and some alkali-feldspars in a reasonable quantity either. Energy spectrum data show that supermicro spherical objects have high content of C which is 54.8% on average by 102 energy spectrum analyzed points. The highest one can reach up to 80.23%. P and S are detected as well which suggest a biological origin.

These supermicro spherical objects have a preferable conformity with oil-bearing intervals which are mainly produced in tuff, indicating a volcanic and hydrothermal activities geological setting. It could be a kind of thermophilic archaea, which is an important hydrocarbon generation material in this district. There is significant sense of further study on the supermicro spherical objects in reestablish the regional background and clarify the hydrocarbon generation mechanism.

References:

[1] LIU Y Q et al. (2013) Acta Sedimentologica Sinica 31(5): 773-781

[2] ZHU G H et al. (2014) Marine Origin Petroleum Geology, Earth Sciences 19(1):1-7

[3] JIANG Y Q et al. (2015) Petroleum Exploration and Development, 42(6):741-749