Study Of Hydrothermal Processes And Hydrothermal Reservoir On Ordovician At Shunnan Area,Central Of Tarim Basin

With the previous studies in in Shunnan area,central of Tarim Basin,data of well logging,core observation and thin section analysis,this paper concluded the rock types,diagenesis characteristics and diagenesis sequence in the lower-middle Ordovician at study area.The rock tapes are micrite,grain limestone,algal limestone,dolomite,silicolite,the micrite is the main rock type in study area.The diagenesis have positive and negative effects on reservoirs.The dolomitization,silicification,dissolution,karstification and fracturing can change the pore structure effectively on carbonate reservoirs.The cementation,compaction and pressure solution,and pyritization destroyed the primary-texture of pore of reservoirs.Based on the observation of thin section analysis and geochemical characteristics,analyzed the mechanism of dolomitization and silicification and established the model of this two diagenesis in the study area.According to the characteristics of dolomite can divide it into five types,including powder to crystallite dolomite,powder to fine grained dolomite,powder to fine grained euhedral dolomite,medium to coarse grained dolomite and saddle dolomite.The dolomite experienced four different dolomitization,such as seawater dolomitization,subsurface burial environment dolomitization,early hydrothermal dolomitization and late hydrothermal dolomitization.The hydrothermal dolomitization have signification influence on hydrothermal reservoir.The study area experienced two kinds of silicification.The early silicification blocked the development of reservoir.The late silicification was formed at late Hercynian related to the activity of hydrothermal fluid.The dissolution pores and incomplated fracture could provide reservoir space to the hydrothermal reservoir.With the preliminary work.Conclusions can be drawn as follows: lower-middle Ordovician experienced two hydrothermal processes in the study area.The one was happened at late Ordovician to Silurian,The other one was at Permian.The first hydrothermal process shown the features of medium to coarse grained dolomite which was not luminous through cathode ray.The hydrothermal fluid was acidic magmas coming from deep underground,pushed by the compaction of consolidation and fracture system to the most of the study area.The characteristics of second hydrothermal process were saddle dolomite which came out bright red light through cathode ray at the border of dissolution pores and silicified quartz crystal.The hydrothermal liquid was the post magmatic fluid rich in silicon and was controlled by the fracture system.The reservoir space for the hydrothermal reservoir were mainly about dissolution pore,dissolution vug,and the irregular fracture.The hydrothermal reservoir at study area can be divided into limestone hydrothermal dissolution vug reservoir,silicolite hydrothermal dissolution reservoir by the genetic type.The limestone hydrothermal dissolution vug reservoir is the main hydrothermal reservoir at study area.The available data shows that the development of this type of reservoir was controlled by the fracture,and the reservoir was made up by the microcrystalline limestone and grain stone and was mainly existed in the Yijianfang formation.The silicolite hydrothermal dissolution reservoir was seen at the upper Yinshangzu on well Shunnan 4 and 401.It was controlled by the fracture,especially more developed at the tensile fracture area.