Origin of authigenic zeolite and its influence on reservoir development in glutenites of the Middle–Upper Permian in Fukang Sag, Junggar Basin

The origin of authigenic zeolites and the main reservoir space types in glutenite reservoirs of the Middle–Upper Permian in the Fukang Sag, Junggar Basin, remain unclear. This study utilizes methods such as optical microscope, scanning electron microscope (SEM), energy spectrum analysis, and X-ray diffraction (XRD) analysis to investigate occurrence characteristics, as well as the origin and its influence of authigenic zeolites on reservoir development in the glutenite reservoirs. The results are as follows: (1) Laumontites are identified as the predominant authigenic zeolites, with minor occurrences of analcimes in poikilitic and interparticle-pore filling forms. (2) Early-stage poikilitic laumontites and analcimes formed during phase A of eodiagenesis, while middle-stage interparticle-pore filling laumontites and analcime formed during phase B of eodiagenesis. Late-stage replacive laumontites formed during late phase A and phase B of mesodiagenesis. (3) The materials for early-stage zeolites originated from the hydration–hydrolysis of plagioclase and magmatic rock fragments, and the dissolution of CO₂ from biological degradation, which formed through the hydration and albitization of plagioclase. Middle–late stage laumonites, related to the dissolution of plagioclase and magmatic rock fragments by organic acids and CO₂ due to thermal evolution of kerogen, formed through plagioclase albitization and analcime alteration in Ca²⁺-rich solutions. (4) The glutenite is characterized by “intense dissolution of zeolite and no (or weak) dissolution of calcite”, with the intergranular laumontite dissolution pores being the most important type of reservoir space. The intense dissolution of laumontites significantly enhances reservoir quality and is a key controlling factor in the formation of glutenite reservoirs.