Chemical Characteristics Of Ordovician Formation Water And Its Relationship With Hydrocarbon Accumulation In Tazhong-Tabei Areas,Tarim Basin

The relationship between formation water and hydrocarbon accumulation is inseparable.Studying the chemical characteristics of formation water is of great significance for analyzing the origin and evolution of formation water and discussing its relationship with hydrocarbon accumulation.Significant progress has been made in the exploration and development of the Tarim Basin in recent years,and a large amount of data on formation water has been accumulated.By collecting the formation water data of the Ordovician and the overlying Silurian Carboniferous in the Tazhong and Tabei areas,on the basis of screening the data,the chemical characteristics of the Ordovician formation water in the Tazhong and Tabei areas were analyzed in this thesis.The origin and evolution characteristics of formation water and its relationship with hydrocarbon accumulation in study area are also analyzed,and the following understandings were obtained:(1)The Ordovician formation water in Tazhong area has relatively high TDS.The salinity increases first and then decreases vertically.The TDS in the central part of the Tazhong area is high,and is relatively low in the eastern and western parts.The ionproportionality coefficients are reductive,indicating that the sealed condition is well.The TDS of Ordovician formation water in Tabei area is higher than that in Tazhong area.It gradually decreases vertically and the TDS is higher in the north of the pinch-out line and gradually decreases in the south in the plane.The ion-proportionality coefficients indicate that the present formation is also well sealed.(2)The formation water in the Tazhong area is a mixture of seawater and paleo-meteoric water,it is typical sedimentary-buried water.The formation water has undergone albitization,dolomitization,and TSR.The formation water mainly comes from the Lower Cambrian;In Tabei area,the formation water is also a mixture of seawater and paleo-meteoric water,and affected by burial and hydrothermal action,it is also typical sedimentation-burial water which has experienced albitization,dolomitization,TSR,and BSR.The formation water may come from Overlying Silurian,Carboniferous and lower Cambrian.(3)In the Tazhong area,contemporaneous karst,weathering crust karst and buried karst occurred under the influence of water.However,the paleo-reservoir was also damaged by water washing and biodegradation,but the damage degree was weak.There is a well correlation between crude oil density and TDS on the plane.The high TDS and reducing ion-proportionality coefficients indicate that the formation conditions are favorable for the hydrocarbon accumulation and preservation.Tabei area also undergoes the karstification under the influence of water,but it is significantly different from that in the Tazhong area in terms of formation time and evolution characteristics.The paleo-meteoric water caused a stronger degree of damage to the oil and gas reservoirs formed in the Late Caledonian,and reservoirs in structural highs are again affected by meteoric precipitation in the Late Hercynian.The formation of high salinity formation water in the northern area is mainly related to the solute diffusion in the high salinity fluid form the overlying strata.But the overall high TDS and reducing ion-proportionality coefficients still indicate that the current formation is well sealed,which is conducive to the accumulation and preservation of hydrocarbons.