Print this pageThe Features and Distribution of Lower Paleozoic Dolomite Reservoir in Tarim Basin, Northwest China
Shen, Anjiang 1; Zheng, Jianfeng 1; Qiao,
Zhanfeng 1; Luo, Xianying 1
(1)Hangzhou Institution of
Petroleum Geology, Petrochina, Hangzhou, China.
Based on the observation of cores and thin-sections from 60 wells, in combination with paleogeography and paleoclimate setting, and geochemistry data, the dolomite reservoir of lower Paleozoic (Cambrian- Ordovician) in Tarim basin is divided into 4 types in origin.
Evaporitic Tidal-flat Dolomite Reservoir occurred in the evaporitic intertidal-supertidal environment, characterized by the deposits of gypsodolomicrite, in which the types of porosity are gypsum-dissolved pores and interbreccia pores. High Fe, Na, P, and Sr, and low Mn contents of the dolomite result in the non- or dark brown- colored CL. The 18O and 13C value of the dolomite is higher than -4‰PDB and -1‰PDB, respectively. The 87Sr/86Sr ratios vary ranging from 0.7085 to 0.7100.
Evaporitic Platform Dolomite Reservoir occurred under the lagoon at the oceanward side, featured by the fabric-selectively dolomitized algae mound or grainstone, in which the types of porosity include moldic pores, gypsum-dissolved pores, and intergranular pores. High Na, P, Mn, and Sr, and low Fe result in the bright brown-orange CL. The 18O, 13C values and 87Sr/86Sr ratios of the dolomite are similar to those of the evaporitic tidal-flat dolomite, however, the Mg/Ca ratios are higher compared to the evaporitic tidal-flat dolomite.
Burial Dolomite Reservoirs consist of the finely, mediumly, coarsely crystallized dolomite, in which pores include mainly intercrystalline pores and intercrystalline dissolved pores. The increasing temperature in burial diagenetic environment caused the depleted 18O value(<-4‰--10‰PDB) of the dolomite. The 13C values are slightly depleted or weakly enriched (-3‰~2‰PDB). The 87Sr/86Sr ratios of dolomite are higher than sea water at that time, as a result of recrystallization. The homogenization temperatures of fluid inclusions in dolomite show the variation from 70°C to 130°C.
Hydrothermal Dolomite Reservoir is characterized by the crystalline dolomite influenced by the hydrothermal fluids and their accompanying hydrothermal minerals. The dolomite shows the variation in 18O value from -9‰ to -17‰PDB, which is depleted significantly less than of the calcite precipitated from meteoric water. The 87Sr/86Sr ratios of the dolomite vary in range from 0.7090 to 0.7100. The hydrothermal dolomite has higher Mg/Ca ratios compared to the evaporitic tidal-flat dolomite. The homogenization temperatures of fluid inclusions in the dolomite vary in range from 110°C to 240°C.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.