Tectonic Characteristics Of The Cen'gong Block In Guizhou Province And Its Effects On Shale Gas Preservation

Cen'gong shale gas block is located in the southwest of China,it's tectonic position belongs to the complex tectonic deformation zone of Guiyang.This area has developed a series of Lower Cambrian organic rich Niutitang Formation shale with a large deposition thickness,wide distribution,as well as moderate buried depth.It has good hydrocarbon generation and the huge shale gas resources potential.However,because it is located in the complex tectonic area and there are large-scale faults and folds which affects the preservation of shale gas,no breakthrough has been made so far.Therefore,it is particularly necessary to strengthen the study on the tectonic characteristics of the area and its effects on preservation conditions.Based on the previous research results,this paper takes Guizhou province Cen'gong shale gas block as study object,using geological,seismic,drilling and logging data,a fine interpretation of the faults tectonic styles of the main seismic sections,an analysis of faults and folds deformation characteristic,an investigation of Cambrian faults system and a division of faults level have been made.By using 2D balanced-section technique to make clear tectonic evolution characteristics of study area.Combined with the analysis of burial history,characteristics of faults and fractures,tectonic styles,conditions of the roof and floor and regional caps,formation pressure and so on,as well as compared with the shale gas block such as Jiaoshiba block,take a comprehensive analysis of the tectonic characteristics effects on shale gas preservation conditions,establish evaluation standard of tectonic preservation conditions.The main research results are as follows:The high dip-angle reverse faults and folds in Cen'gong block are well-developed,which are dominated by NE and NNE.The NNE fault system is mainly formed in the period of Yanshan movement and Himalayan movement,and the NE fault system is a complex fault system formed in many stages.The folds are mainly separated trough-type folds.Back thrust faults are often developed on the two wings of the wide and slow anticlines,and hedging thrust faults are often developed on the two wings of the closed synclines.The structure in the centre and south of the study area is stable,with relatively few faults and folds,mainly shown as wide and slow anticlines or a broad and slow saddle structure held between the anticlines.The structures in the area are mainly compressional and have strike slip properties.The Niutitang Formation mainly develops structural fractures,including high dip-angle shear fractures,high dip-angle tension fractures,high dip-angle twisting fractures and low dip-angle detachment fractures.Non-structural fractures are mainly bedding fractures.The tectonic evolution of Cen'gong shale gas block is consistent with the regional tectonic evolution of the upper Yangtze platform,which has clear stages,can be divided into the late Mesoproterozoic to Silurian development stage,the late Triassic development stage of the Devonian period and the Mesozoic Cenozoic development stage.It has the characteristics of early and medium term continuous burial,stable hydrocarbon generation in the middle and late stage,moderately uplift and transformation in the later stage.The strata pressure of the Niutitang formation is generally not high,showing a low and normal pressure status.Based on the tectonic evolution and burial history,development characteristics of faults and fractures,tectonic styles,the roof and floor and regional caps,formation pressure and other key factors,the evaluation standard of tectonic preservation conditions are established and the favorable area prediction from the tectonic angle is carried out.The results show that the most favorable area for tectonic preservation of shale gas is around TX 1 well.