Control Of Tectonic Evolution On Shale Gas Enrichment In Lower Silurian,Xiuwu Basin

The Upper Ordovician Xinkailing formation and the first member of Lower Silurian Lishuwo formation in Xiuwu Basin has a good hydrocarbon-generating material base.However,the gas reservoir was strongly restructured and the controlling effect of tectonic evolution on shale gas enrichment is not clear.So,further research is needed.In this paper,the logging indicators of formation elements,combined with core data,field profiles and conventional logging data are used to analyze oxidation-reduction environment and biological productivity,so as to identify the influencing factors of organic matter enrichment.Through the establishment of burial history,thermal history,hydrocarbon generation and expulsion history,the evolution process of reservoir control conditions is analyzed,and the control of tectonic evolution on shale gas enrichment is finaly clarified,and favorable areas are predicted finaly.During the depositional period of the target layer,the intense tectonic movement triggered the hydrothermal activities,resulting in the water anoxia and higher biological productivity,further controlling the enrichment of organic matter.Finally,shale with siliceous minerals and high TOC content were formed.From Caledonian to early Indosinian,the tectonic activity in the study area was weak.The strata settled steadily and the shale gas content increased rapidly.From the late Indosinian to the early Himalayas,the extensional action was strong,forming a large number of faults,which accelerated the shale gas loss.Compression in the late Himalayas closed the fault and slowed the rate of gas loss.The key time of reservoir formation and enrichment in the study area is Triassic to Jurassic.The evaluation units are divided according to the buried depth,the fault and the structural position.The preservation conditions are evaluated from the static aspects,such as the nature and scale of the fault,the distance from the fault and outcrop,the dip angle of the formation,the self-sealing of shale,the sealing of the roof and floor,and the dynamic process of denudation thickness,the time when shale stopped generating gas.The results show that Laopengli area is the favorable exploration area.