Research On Effect Of Structure On The Shale Gas Accumulation In Niutitang Formation In Block 3 Of Fenggang,Qianbei Area

In the exploration process of conventional oil and gas with the Sichuan basin as a representive,it is clear that there is great exploration potential of shale in the north of Guizhou.The block 3 of Fenggang is located in the northern Guizhou Province.It is affected by multi-period tectonic movements,and the geological conditions are very complex,which restricts the exploration of shale gas to a great extent.This paper takes the black shale of the lower Cambrian Niutitang Formation in block 3 of Fenggang as a research object and definites the Niutitang Formation deformation mechanism under the action of tectonic transformation,reservoir characteristics and gas-bearing properties features basing on systematic analysis of tectonic development characteristics and then analyses the preservation conditions of shale gas combining with structural characteristics.The study area is located in the the Fenggang north-south trough-like fold deformation zone what is included in the north Guizhou uplift zone and it has the typical characteristics of Jura-type Fold.The deformation of the synclines is strong and the pressure faults frequently develop;The anticline deformation is relatively weak and it is the typical thin-skinned structure,which is the product of complex detachment of the shallow crust;The main slip surface may be the weak layer in the lower Cambrian.The structural feature is mainly folds and faults and the preferred direction of it is mainly the nearly SN,NNE and NE.The properties of the reservoir has changed greatly under the action of tectonic reformation and the TOC of the black shale in the Niutitang Formation is 0.3%~28.1%;Vitrinite reflectance(Ro)is 2.66%~2.95%,what indicates organic matter is in over mature evolutionary stages.The pore system in the study area is complicated and the shale gas mainly exists in the pore system in the free form.The black shale of the Niutitang Formation in the study area has good hydrocarbon generation capacity but the formation age is old.It is influenced by multi-periods tectonic movement and the structural evolution is complex and the preservation condition is the key to the shale gas accumulation.To definite the preservation conditions of the the black shale of the lower Cambrian Niutitang Formation,seismic interpretation and structural evolution analysis are used,combining with the studying on material basis,the top and bottom and regional caprocks,gas composition,formation pressure and other factors on shale gas preservation conditions.The results show that the action of strong thrust nappe structure in the Stage of Yanshan has formed the typical trough-like fold this area,accompanied by large faults and strong uplift denudation.Contrast TX-1 well with high CH4 content and FC-1 well with low CH4 but high N2 content can be found that the development of high angle fractures has a great influence on shale gas preservation.On the whole,well preserved areas of shale gas for the study area is the paleo uplift region near faults,where the hydrothermal ore deposits and high angle fractures is not developed and the later tectonic transformation has little effect.