Genetic Type And Accumulation Characteristics Of Natural Gas In The Kelameili Gas Field,Junggar Basin

Hydrocarbon migration and accumulation mechanism is one of the key scientific problems that must be studied and answered when carrying out hydrocarbon exploration in the deeper formation of the superimposed basin developed in the Northwest China.The Kelameili natural gas field is the only gas reservoir that developed in the volcanic reservoir in Northwest China,which makes it a unique example to answer the above scientific questions.Research results can also provide valuable information to guide the natural gas exploration in the deeper formation of the Junggar Basin.Research work is focused on the space distribution of the source rock,the genetic types of the natural gas and the mechanism of hydrocarbon migration and accumulation based on the abundant organic geochemical data both from the source rock and from the natural gas composition,and the carbon isotope data from different natural gas components.The following conclusions are drawn:The main source is from the Carboniferous Formation,which can be divided into the lower Dishuiquan segment and the upper Bashan segment.Both of them are distributed in the Dongdaohaizi sage to the east and the Dishuiquan sag to the west and the source rock is characterized by type III kerogen and medium-high abundance.However,the maturity in the source rock from the Dongdaohaizi sag is high(Ro>1.5%),while that from the Dishuiquan sag is relatively low(1.2%<Ro<1.5%).The natural gas has relatively complicated components in that some samples are high concentration in ethane and the above,nitrogen and carbon dioxide,while others are relatively high concentration in methane.Their maturation is also variable indicated by the isometric/normal alkane ration.However their genetic types fall uniquely into the thermogenic coalbed natural gas indicated by the concentration of different component and their carbon isotopic ration.Natural gas migration and accumulation happened mainly at the late Indosinian and the middle Yanshan.The natural gas with low maturity is mainly from the Dishuiquan sag,while the natural gas with high maturity is mainly from the Dongdaohaizi sag.The model for the natural gas migration and accumulation is simplified as long-distance lateral gas migration and accumulation along the faults.The low maturity natural gas sourced from the Dishuiquan sag migrated eastward and the high maturity natural gas sourced from the Wucaiwan sag migrated westward along the Dixi fault and accumulated in the traps on their way.Mixture happened on the well DX18 district as indicated by the isotopic reversal.