CHARACTERISTICS AND INFLUENCING FACTORS OF CARBONIFEROUS VOLCANIC RESERVOIRS IN HASHAN AREA, NORTHWESTERN MARGIN OF THE JUNGGAR BASIN

As important exploration targets at the northwestern margin of the Junggar basin, Carboniferous volcanic rocks formed under the background of continental island arc and oceanic island arc. In order to study the development and controlling factors of volcanic reservoirs in the Hashan area, based on outcropping observation, through studying core, ordinary and cast thin sections, scanning electron microscope and other means, combined with FMI analysis, the petrological characteristics, reservoir characteristics and influencing factors of volcanic rocks were explored. It is believed that Carboniferous volcanic rocks are mainly composed of five lithological types, which can be classified into two classes, including lava-formed rocks, such as basalt and andesite, and pyroclastic rocks, such as volcanic breccia, tuff and sedimentary tuff. There are 16 types of reservoir space, which can be classified into three larger types that are corrosion-fracture type, fracture-corrosion type and corrosion type. Lithology and lithofacies are the internal factors affecting the reservoir, while weathering, leaching and tectonics are the external factors. Weathering and leaching mainly occur under the weathering crust, the interface of volcanic eruption cycles and the interface of eruption periods. Moreover, a large number of fractures are generated by tectonism, which can not only improve the percolation performance of reservoirs, but also effectively increase the storage space. The weathering crust at the convergence zone of faults and the development areas of volcanic breccia, tuff and andesite at the interfaces of eruptive cycles and periods are favorable reservoir areas. This study provides a basis for predicting the favorable reservoir distribution of carboniferous volcanic rocks in the Hashan area and a theoretical support for exploration and deployment.