BACKGROUND Mineral composition and its microscopic characteristics are of great significance to the study of sedimentary environment, rock framework and reservoir space of oil and gas reservoirs.

OBJECTIVES To investigate the mineral composition, content and spatial distribution of carbonate core samples of the Permian Longge Formation and provide the basis for oil and gas evaluation of the Paleozoic carbonate reservoirs in Qiangtang Basin.

METHODS The sample was analyzed by hyperspectral scanning and QEMSCAN.

RESULTS The Longge Formation is dominated by microcrystalline limestone and granulated limestone, and the minerals are mainly calcite and dolomite, the contents of which are generally greater than 90%, followed by quartz and a minor clay mineral and feldspar. The mineral composition has obvious characteristics of longitudinal segmentation. The contents of calcite and dolomite are higher in the upper section. The content of dolomite in the middle section is higher, and the degree of dolomization is relatively strong. The porosity and permeability of this section have decreased. The lower section is mainly composed of calcite. In addition, the analysis of clay mineral characteristics shows that the Longge Formation has experienced complex sedimentary-diagenesis and late thermal disturbance and fluid replacement, which has a strong impact on oil and gas migration and preservation in this area.

CONCLUSIONS Hyperspectral scanning technology can be used to quickly and efficiently interpret large-scale mineral features. QEMSCAN enables more precise and quantitative analysis of mineral microscopic features. The Longge Formation is dominated by carbonate and obviously affected by diagenesis and the local dolomization is strong. The oil and gas conditions in this formation are poor.