天然气水合物成藏要素及其时空耦合初探——以青藏高原昆仑山垭口多年冻土区为例

Preliminary discussion on the space-time coupling of natural gas hydrate accumulation elements:A case study from Kunlun Pass permafrost regions,Qinghai-Tibet Plateau

针对青藏高原昆仑山垭口多年冻土区表层地质、钻探和测井等表现出的地表浅层赋存大量烃类和非烃类气体的现象,结合该区地质资料和天然气水合物最新勘探成果,利用"天然气水合物油气系统"的概念和理论,从气源、温压、水源、运聚等关键要素详细分析了昆仑山垭口多年冻土区天然气水合物的赋存条件。并以该区地质演化历史为依据,探讨了诸多成藏要素的时空匹配和耦合关系。结果表明,昆仑山垭口多年冻土区先后经历了晚三叠世末期—新近纪晚期大量热解气形成与散失,部分热解气残留,新近纪末期羌塘组沉积,晚更新世高原隆升、冰川冻土形成,晚期新构造运动产生断裂、裂缝沟通深部残留热解气进入浅层水合物稳定带与羌塘组少量微生物气混合形成天然气水合物等多个阶段。该区赋存的天然气水合物具有晚期成藏的特征。

A large number of hydrocarbon and non-hydrocarbon gas which may be decomposed from natural gas hydrate are found in the surface layer of Kunlun Pass Basin permafrost regions Qinghai-Tibet Plateau by the surface geological anomalies,shallow holes drilling and logging.Based on the geological data,natural gas hydrate exploration results,and the concept of＂natural gas hydrate petroleum system＂,gas hydrate forming key elements in Kunlun Pass permafrost area are analyzed in detail,which include gas source,temperature,pressure,water and migration-accumulation.And based on the geological evolution history of this area,the space-time matching and coupling relation of many reservoir forming factors are discussed.The results showed the formation of gas hydrate in Kunlun Pass permafrost area has experienced multiple stages.First stage,plenty of hot gas formed and dissipated from late Triassic to Late Neogene,and part of the pyrolytic gas was kept in the formation;Second stage,Qiangtang Formation sediment in the Late Neogene and Late Pleistocene with plateau uplift,the glaciers and permafrost came into being;Final stage,deep residue pyrolytic gas migrated along the fracture and crack which were generated by new tectonic movement.When it moved upward into the shallow hydrate stability zone,and mixed with biogenic gas forming in Qiangtang Formation,the gas hydrate came into being.Natural gas hydrate has the characteristics of late hydrocarbon accumulation.