Characteristics and Genesis of Alkaline Lacustrine Tight Oil Reservoirs in the Permian Fengcheng Formation in the Mahu Sag, Junggar Basin, NW China

Through optical microscopic examination, scanning electron microscope analysis, whole rock X-ray diffraction fluorescence spectrum carbon and oxygen isotope temperature measurement of fluid inclusions, the characteristics formation mechanism alkaline lacustrine tight oil reservoirs Permian Fengcheng Formation in Mahu Sag Junggar Basin have been systematically studied, a genetic model has proposed. Porosity is mostly less than 4%, with permeability 0.1 mD. The lithology mainly tuff, authigenic minerals consist feldspar, quartz, dolomite, salt (e.g., shortite, trona). feldspar quartz originate from devitrification volcanic glass pyroclastic rocks. Reservoir space dominated by dissolution pores minerals, followed intercrystalline among other formed devitrification. Fractures are comprised shrinkage fractures, structural bedding seans. was an lake Sag, sedimentary setting plays decisive role Formation. Volcanic generally devitrified within diagenetic early stage, micropores become important reservoir space. Feldspars were dissolved acidic fluids generated burial thermal evolution source rocks which produces most developed reservoir. abnormal high pressure hydrocarbon generation expulsion one main reasons for porosity preservation. In environment Formation, widespread dolomitization precipitation large number stage resisted partial compaction, not only effectively protected porosity, but also provided material conditions enhancement.