Characteristics Of Structural Deformation And Its Relationship With Oil And Gas In The Southern Sichuan Basin

Sichuan Basin is an important petrol-bearing basin which has experienced multistage tectonic evolution.And the southern Sichuan Basin is an important gas-bearing area.Its structural characteristics and the influence of tectonism on the formation of gas reservoirs have always been concerned.The paper is based on the structural interpretation of seismic data,combined with ground geological survey,guided by modern structural geology principles and basin analysis method,the structural styles,fault characteristics,structural evolution and main tectonic controlling factors in the southern Sichuan Basin analyzed.Finally,the controlling effect of structural deformation and evolution process on hydrocarbon accumulation is analyzed by integrating oil and gas geological data.Separated by a slip layer,the southern Sichuan Basin can be divided into 4deformation layers: the Sinian-Middle Cambrian at the bottom,the Middle CambrianLower Silurian at the deep,the Lower Silurian-Middle Triassic at the middle,and Upper Triassic-Cretaceous at the shallow.The bottom deformation layer had weak deformation and the deep deformation layer had abundant structural styles.The middle and shallow deformation layers had inharmonious deformation in the “horse hoof” type area around the north part of the the south Huaying Mountain fault-fold belt,middle and north parts of the broom-like fault-fold belt and the east part of the Chishui tectonic belt,which is identical with the distribution of the three detachments.The structural styles include popup,triangle zone,imbricate fan and duplex.The deformation is controlled by regional dynamic conditions,paleo-uplift and detachment layer distribution.During Yanshanian tectonic cycle,Yongchuan broom-like fault-fold belt began to develop by the tectonic activity of Xuefeng mountain thrust belts on the eastern Sichuan Basin.The south Huaying mountain fault-fold belt began to form by the tectonic activity of the SongpanGarze fold belt on the western Sichuan Basin.Chishui tectonic belt was finally finalized by the tectonic activity of the the Daliang mountain tectonic belt on the southern Sichuan Basin.The Luzhou paleo-uplift affected to be a stress spacer.The middle Cambrian transmitted stresses for deformation and affected whole area deformation together with the lower Silurian detachment.The lower and middle Triassic detachment mainly affected the northeast “horse hoof” type area.Tectonic folds provide traps and faults provide migration channels for oil and gas,and the fractures associated with the faults improve the carbonate reservoir conditions which jointly affect the oil and gas accumulation in southern Sichuan Basin.With the transformation and adjustment of late tectonism,the present oil and gas distribution pattern was finally formed in the southern Sichuan Basin.In the future,the deep exploration direction in the southern Sichuan Basin may be the fault-block trap of deep deformation layer,the gentle slope shale gas with relatively weak structure and the subsalt structure-lithologic trap of bottom deformation layer.