关键词: 西北地区, 侏罗系, 煤系, 油气田, 条件, 油气分布

Abstract: The formation of coal measure-derived oil ggs fields in NW China is the product of the assemblage in spatial and temporal domains of certain tectonic conditions,sedimentology and the accumulation of oil-prone organic materials as well as the effective expulsion of oil gas from the coal measures.The study made by this paper shows that the following.conditionsare necessary for the formation of coal measure-derived oil gas fields in Jurassic sequence of NW China The Jurassic original basin,which was occupied by lake water or low-positional swamp during the most Jurassic time,should exist,so that the complete association of source rock,reservoir and caprock was well developed;The original depositional environment was characterized with low and gentle depression and humid climate which are favorable for the development of low-positional marshland and lake where the oil-prone organic materials were accumulated with large volume;The sequent basin should occur on the Jurassic original basin which is necessary to keep the coal measure source rocks in the condition of progressive mat uration,and certain degree of tectonic compression taking place soon after the maturation of source rocks can provide the driving force for the effective expulsion of oil gas from the coal measures.Coal measure-derived oil gas fields is horizontally distributed along the inner side of lake strandline depositing with source-rock and vertically occured above or below the thresh old of maturity.Owing to the sharp variation of lithology and facies in coal measures,the lithological and composite types of oil gas pools play a big role in the petroleum accumula tions of coal measure sequence.

Key words: NW area, jurassic system, coal measures, oil and gas fields, condition, oil and gas distribution