塔东热液地质作用机制及对储层的改造意义

Mechanism of Geological Activities of Eastern Tarim Basin Hydrothermal Fluids and Its Significance in Reservoir Transformation

塔东地区断裂发育,早期发育的断裂与晚期断裂之间存在相互改造、叠加、复合的过程,深大断裂沟通多套地层,断裂活动期形成的挤压破碎带和断裂裂缝带作为岩浆热液上升通道,为热液溶蚀作用改造储层提供了有利条件,因此,识别出热液期次对塔东白云岩储层成因机制具有重要意义。通过对钻井岩芯、岩屑及岩石薄片、铸体薄片观察鉴定分析,在区内下古生界碳酸盐岩中识别和发现了钠长石化作用和自生羽毛状伊利石沉淀,也是塔里木盆地内的首次发现,并通过对包裹体均一温度,碳氧同位素等地化特征研究,揭示其成岩流体源于岩浆热液,丰富了区内热液作用的矿物学标志,进一步识别出区内存在3期热液作用,通过对3期热液作用的机制及其储渗空间意义的研究,总结出第Ⅰ期热液作用对于储层形成意义不大,第Ⅱ期热液作用主要发育在局限的沉积环境,第Ⅲ期热液溶蚀形成溶蚀缝孔洞,与天然气运移聚集匹配良好,构成了区内天然气聚集成藏的主要储渗空间。

Faults developed in the Eastern Tarim Basin.Early and late faults underwent processes such as mutual transformation,superposition,and recombination,and deep faults run through multiple strata.Compresso-crushed zones and fracture zones that were formed during fault activities function as the ascending passage for magmatic hydrothermal fluids and provide favorable conditions for reservoir reconstruction by hydrothermal dissolution.As such,identifying the hydrothermal activity stage is crucial for understanding of the mechanism of dolomite reservoir formation in the Eastern Tarim Basin.By observing,identifying,and analyzing drilling cores and fragments,rock thin sections,and casted rock thin sections,albitization and featherlike authigenic illite precipitation were identified and discovered in the Lower Paleozoic carbonate rocks for the first time in the Tarim Basin.By studying geochemical properties such as the homogenization temperature,and oxygen and carbon isotopes of the inclusions,the source of the diagenetic fluids was found to be magmatic hydrothermal fluids.This finding supplements the mineralogical indications of hydrothermal activities in the region.The study further identified the existence of stage-three hydrothermal activity,and by investigating its mechanism and significance in the reservoir space,it was concluded that stage-one hydrothermal activity does not play a key role in reservoir formation.Stage-two hydrothermal activity is mainly developed in constrained sedimentation environments.Stage-three hydrothermal dissolution forms dissolution fissures and cavities that are favorable for the migration and accumulation of natural gas,and therefore,the fissures and cavities serve as the main seepage passage for natural gas accumulation and reservoir formation in the region.