Formation Mechanism and Enrichment Regularities of Kelasu Subsalt Deep Large Gas Field in Kuqa Depression,Tarim Basin

It is well known that there were rich gas resources in Kuqa Depression.Since the discovery of Kela-2large gas field,Dabei gas field and Keshen gas field have been discovered in the down block of Kelasu fault in Keshen structural zone.Taking Keshen and Dabei gas fields as an example,formation mechanism and enrichment regularities of Kelasu subsalt deep large gas field were discussed in detail in this paper.It was considered that the Jurassic-Triassic coal-measure source rocks were a high effective gas kitchen,gas generation intensity and rate reached the maximum(corresponding to(160-320)×108 m3/km2 and 15-20mg/gTOC·Ma,respectively)in recent 5Ma.Kelasu structural zone overlapped the hydrocarbon supplying centers,and sufficient gas source supplied a material basis for gas accumulation of Dabei-Keshen gas field. Regionally distributed thick gypsum rock restricted structure thrust breakthrough,protected reservoirs effectively and preserved oil and gas with high-efficiency,which provided an important assurance.Beddingdelamination contractional deformation,subsalt imbricated thrust structures and widely distributed low porosity sandstone reservoir provided a favorable storage space for oil and gas accumulation in Dabei-Keshen area.The formation of subsalt deep structure is related to compressional deformation as a result of later Himalayan episodic strong thrust compression.Pliocene-Quaternary is the main stage for the formation of Kelasu structural zone and the main structure finalized in Middle-Later Kuqa Formation.Gas generation history research showed the main gas generation stage began in sedimentary period of Kuqa Formation. Later high-efficiency oil and gas accumulation of Kelasu subsalt structural zone was determined by a better match of main gas generation stage and structure forming stage,which is an important reason for the formation of deep large gas field in Kelasu play zone.