Origin of natural gas in the Kelameili Gas Field in the Junggar Basin and its periphery:Re-understanding and its implications for natural gas exploration
The Kelameili Gas Field is the largest gas field that has been discovered in the Junggar Basin,and its Carboniferous gas reservoirs have the proved natural gas in place of 832.4×108 m3.In order to further explore,evaluate and determine the natural gas source potential in the Kelameili Gas Field and its periphery and drive the discovery of new gas fields,this paper analyzes 65 natural gas samples taken from 5 reservoirs and 38 wells.Then,based on the components and stable carbon isotope compositions of natural gas,its origin and secondary reworking are researched systematically,and the potential natural gas exploration fields are pointed out.And the following research results are obtained.First,the origin of natural gas in the Kelameili Gas Field and its periphery is classified into four types,among which,type Ⅰ and Ⅱ are coal-derived gas,type Ⅲ is secondary biogenetic gas derived from the shallow associated oil through biological degradation(mixed thermogenic gas)and type Ⅳ is oil-type gas.Second,the Δδ13C(C3-C2)and i-C4/n-C4 values of some natural gas samples increase abnormally,indicating that their heavier-hydrocarbon-gas components were selectively degraded by bacteria.Third,compared with the Batamayineishan Formation source rocks,the Dishuiquan Formation source rocks have wider distribution,better continuity and larger scale.The Pingdiquan Formation source rocks have generally reached high to over-mature stage in the southern Junggar Basin.The petroleum system with the Dishuiquan Carbonifeous Formation and Pingdiquan Permian Formation source rocks is a potential new field for large-scale exploration of deep and ultra-deep natural gas in the Junggar Basin.Fourth,secondary biogenetic gas reservoir is an important field for efficient exploration of shallow natural gas due to its shallow burial,high methane concentration,low production cost,fast productivity construction and wide distribution in the Junggar Basin.In conclusion,re-understanding the origin of natural gas makes the natural gas resources in the Kelameili Gas Field and its periphery in the Junggar Basin understood further,and reveals that deep and ultra-deep natural gas and shallow natural gas in the Junggar Basin are strategic replacement fields of natural gas exploration.The research results provide an important technological reference for the great transformation from oil exploration to simultaneous development of oil and gas.
Junggar BasinKelameili Gas FieldLower CarboniferousMiddle PermianNatural gasGas source correlationExploration field
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