Characteristics and development model of hydrothermal alteration reservoir of Ordovician Yingshan Formation in northern slope of central Tarim Basin

In the Middle-Lower Ordovician Yingshan Formation in the northern slope of the central Tarim Basin, typical epithermal hydrothermal mineral assemblages, such as hydrothermal quartz, lath gypsum and saddle dolomite, were found in carbonate rocks. For different types of quartz inclusions, measured temperature was significantly higher than maximum evolution temperature. The relation between the Yingshan reservoir distribution in typical wells and the potential unconformities in the study area was studied, indicating that the Yingshan reservoirs generated from hydrothermal alteration, rather than the karstification of meteoric water. The main space of the Yingshan reservoirs was secondary hole (cave) and expansion fracture, with low porosity and permeability. They were divided into 3 types: hole type, hole-fracture type and pore type. Analysis of the main controlling factors of hydrothermal alteration reservoir showed that fault-fracture system was a precondition for reservoir deve-lopment, and the NE and NEE main strike-slip faults of the late Caledonian-Hercynian and the secondary faults controlled the plane distribution of hydrothermal reservoir. Deep hydrothermal fluid altered reservoir, and fluid properties and reservoir lithologic structure controlled the vertical distribution of hydrothermal reservoir. The development model of hydrothermal alteration reservoir was established. Hydrothermal alteration reservoirs, which were featured by big thickness, little affected by depth, and widely developed along main and secondary faults, were new gas exploration fielda of carbonate rocks in the Tarim Basin.