关键词: 塔中地区, 白云岩储层, 热液溶蚀作用, 重结晶作用, 流体包裹体, 同位素组成

Abstract: Dolomite accounts for a significant proportion of the Cambrian-the Lower Ordovician strata of the Tarim Basin,which mainly consists of dark gray powder-fine crystalline dolomite.A lot of shallow gray-white medium-coarse crystalline dolomite is locally developed in the Tazhong area.The maximum frequency of homogenization temperature of the fluid inclusions in the medium-coarse crystalline dolomite ranges from 160 ℃to 200℃,and the salinity is from 6.88% to 14.15%.The δ¹⁸O_PDB values of the medium-coarse crystalline dolomite are from -10.91‰ to -7.65‰,and the average value is -8.98‰,which is lighter than that of the powder-fine crystalline dolomite.The δ¹⁸O_SMOW values of the fluid are from +4.2‰ to +10.2‰ according to the fractionation factor between dolomite and water,such fluid is considered as the hydrothermal fluids.The ⁸⁷Sr-to-⁸⁶Sr ratios of the medium-coarse crystalline dolomite range from 0.709 098 to 0.709 236,and the average ratio is 0.709 171,which is higher than those of the powder-fine crystalline dolomite and the Paleozoic normal marine carbonate.The characteristics of the strontium isotope composition demonstrate that the formation of the medium-coarse crystalline dolomite is relative to hydrothermal fluid.By combining with the occurrence,the medium-coarse crystalline dolomite is predicted to be the recrystallization of the powder-fine dolomite under the effect of hydrothermal fluid.The altered dolomite is good reservoir because it contains abundant intercrystalline pores and dissolution pores.The hydrothermal alteration dolomite reservoir is extensively developed in the Lower Paleozoic of Tarim Basin and should be paid more attention during petroleum exploration of deep hydrocarbon reservoir in the Paleozoic.

Key words: Tazhong area, dolomite reservoir, hydrothermal dissolution, recrystallization, fluid inclusion, isotope composition