The Influence Of Structure On Accumulation Of Shale Gas In Lower Cambrian Niutitang Formation In Cen'gong,Guizhou

Cengong region of southeast Guizhou is located at west side of Xuefeng Mountain and southeast margin of Sichuan Basin,a complicated tectonic deformation zone with trough-like and anticline-like folds,where Niutitang Formation is of favorable exploration potential for shale gas,with high content of organic matter,high degree of thermal evolution and moderate sedimentary thickness.But there is still no gas reservoir in commercial exploitation value after exploration of several wells.In this region,Well TX-1 and Well TM-1 of unlike gas-bearing differ in structural location(the former one is footwall of thrust structure and the latter one is flat)that are inferred to have great impact on reservoirs.This paper researches on Well TX-1 and Well TM-1 to explore the influence of structure of this region on shale gas reservoir according to document retrieval,information collection and sorting,geological survey,geochemical testing,etc.As a result,this formation belongs to the stage of maturity to over maturity,whose maturity of organic matter ranges from 2.5% to 3.5% after structural processes,shale gas is free due to high degree of evolution of organic matter so that reservoirs are required to be of higher degree of porosity and favorable preservation condition.Shale gas of this region occurs in absorbed gas,low content of free gas and lower porosity and permeability as whole.The study has found that free gas in zones of higher content of shale gas of TX-1 Well increases;in terms of structural location,TM-1 Well's evolution of organic matter is higher than TX-1 Well,IH and D of pyrolytic parameter is lower and easier to loss hydrocarbon generation potential;TM-1 Well is relatively of favorable porosity and permeability,but its structural belt has no sealing ability because of the connection of fault and earth surface;TX-1 Well possesses sealing ability for slightly deformation of footwall and more stable flat.As a result of nappe tectonics with west-east ramps and northrn-southern ancient uplift,the landscape of basin formation.Under compressional stress,the central of this region develops approaching multi-faults that pass through Niutitang and Laobao Formation,resulting in reconstructed reservoirs,infiltrated surface water along faults and loss of shale gas.In addition,the outcrop of structural heights is one channel for the loss of shale gas as well.That is to say,this region is of poor preservation condition in terms of structure.In conclusion,factors of structure of this region on shale gas reservoirs are mainly as follows.Firstly,reservoirs reconstruction affects porosity and permeability and occurrence state of shale gas.Secondly,the damage of preservation condition leads to the loss of most shale gas,and shale gas is merely preserved in stable structural region.