In recent years,significant progress has been made in shale gas exploration in southern Shaanxi.The Hanzhong area,located along the northern margin of the Yangtze Plate,is also considered to have promising shale gas resource potential.This study focuses on investigating the geological conditions and evolutionary history of Cambrian shale gas in the Hanzhong area using field geological surveys,2D seismic analysis,petrological examinations,and organic geochemical data.The results show that the Hanzhong area has undergone three stages of geological evolution:marine evolution from the Nanhua to the Triassic period,intracontinental evolution from the end of the Triassic to the Cretaceous period,and Cenozoic rift basin formation.The Cambrian Niutitang Formation and Shipai Formation represent transitional facies deposits,characterized by dark mudstone containing predominantly type Ⅱ 1 and Ⅱ 2 organic matter.These shale formations exhibit a total organic carbon(TOC)content ranging from 0.45％to 2.79％,with a maturity level(Ro)between 0.61％and 1.21％.These characteristics classify them as medium-to good-mature source rocks,indicating significant hydrocarbon generation potential.In addition,the gray-black silty mudstone of the Niutitang Formation is rich in organic matter and contains high contents of brittle minerals such as quartz and clay minerals.This formation also exhibits well-developed micro-fractures and pores,which are favorable conditions for the generation,occurrence,and subsequent development of shale gas.The study concludes that the Cambrian system in the Hanzhong area holds promising shale gas resources,with the geological conditions being more favorable in the eastern part compared to the western part.
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