|
Influences of Feldspar Dissolution on Reservoir Physical Properties of Clastics in the Lower Jurassic Coal Measures, Eastern Kuqa Depression
WU Jin, WANG Bo, ZHU Chao, GONG Qingshun, SONG Guangyong, WANG Hui
2019, 40 (6):
1-1.
doi: 10.7657/XJPG20190603
The dissolution of acid fluids to feldspar is commonly found in the Lower Jurassic coal measures in the eastern Kuqa depression and the thin section analysis shows that a large number of secondary dissolution pores are developed in feldspar and rock debris. Under different diagenesis conditions, feldspar dissolution degree, feldspar dissolution product type and feldspar dissolution product quantity are different, which result in different effects on reservoir physical properties. Based on the analysis of thin section, cast thin section and scanning electron microscope and using whole rock analysis, clay mineral analysis and fluid inclusion data, the paper analyzes feldspar dissolution, diagenetic environment, the differences of feldspar dissolution products and their effects on reservoir physical properties in different diagenetic environments. The study shows that in the Lower Jurassic reservoirs in the Dibei area of the eastern Kuqa depression, the dissolution of feldspar occurs in a relatively closed high-temperature diagenetic environment, the dissolution rate of feldspar is high under high temperature conditions, and fluids flow slowly in this closed diagenetic environment. Therefore, a large amount of feldspar dissolution products precipitate in the intergranular and intragranular pores nearby. When the burial depth is less than 4 000 m （the temperature is less than 110 °C）, the products of feldspar dissolution are mainly silica and kaolinite, the kaolinite is dispersed like dots and the pores are not filled. The intercrystalline pores are developed and have good connectivity so that to some extent, the physical properties of the reservoir are improved. When the burial depth is more than 4 000 m (the temperature is higher than 110 °C), the feldspar dissolution products are mainly silica and illite, the hairy and flaky illite fills the pores in sandstone, leaving no pore spaces, and it is easy to form debris to block the pores, which reduces the porosity and permeability of the reservoir. The dissolution of feldspar in the Lower Jurassic reservoirs in the Tugerming area occurs in a relatively open and shallow diagenetic environment, the products of feldspar dissolution can be effectively brought out of the dissolution zone, and only a small amount of silica and kaolinite precipitate. The feldspar dissolution in this area has an effective pore-enhancing effect on the reservoir
Related Articles |
Metrics
|
