Mesozoic And Present Tectonic Stress Field Around Lichuan County,Western Hubei Province

The eastern part of Lichuan area belongs to wide-spaced synclines belt, which is in western Hunan and Hubei province, and the western part of that area belongs to wide-spaced anticlines, which is in eastern Sichuan province. In the whole, western Hunan and Hubei province-eastern Sichuan province area is characterized by wide-spaced anticlines and synclines belt, which formed in Mesozoic. Longmaxi Formation shale is an important reservoir of shale gas and typical fractured oil and gas reservoir in Jiaoshiba, eastern Sichuan province. For a long time, a great deal of work of the relevant fracture prediction of shale gas fields are concentrated in seismic interpretation and well logging interpretation, while ignoring the key role of tectonic stress field on the fracture growth. The late Jurassic tectonic stress is the foundation of the folds and fauts in Jiaoshiba area, when wide-spaced anticlines and synclines belt formed. The study of present tectonic stress filed around Jiaoshiba area can be used to predict fracture development advantageous area.Through the observation of conjugate shear joints, tectonic characteristics and stratigraphic contact relationships in Lichuan county, a tectonic event in late Jurassic was determined, and the extrusion direction is NW-SE. According to the ultra microstructure of quartz crystal dislocations density method, a value of 44.1MPa? 62.6MPa of the tectonic event was got. Moreover, according to the collection data, the direction of present tectonic stress field, which is SE1200, in Jiaoshiba was determined. The value of present tectonic stress filed in well JY1 is about 12MPa-33MPa in the altitude of-1800m?-4800m. The rocks in the altitude of-1800m?-4800m were divided into three rock series, which were sandy rock group of Xiaoheba-Hanjiadian Formations, mud shale group of Wufeng-Longmaxi Formations and limestone rock group of Shizipu-Linxiang Formations. According to the elastic-plastic increment stress field numerical simulation method, the differential stress contour maps of present tectonic stress field in Jiaoshiba and their characteristics were got.On the plane, the fracture development favorable areas of a layer from altitude of-1800m?-4800m every 600m, were mainly located in the northeast and southwest of Jiaoshiba area. The directions of fracture distribution and the fault strikes were similar. On the vertical, the fracture development favorable areas were larger in altitude of-2400m?-3600m than that of-1800m,-4200m and -4800m. Moreover, the deeper the depth was, the less fracture there were in the center parts. The present tectonic stress field direction maps of a layer from altitude of -1800m?-4800m every 600m in Jiaoshiba area, western Hubei, were got through method of elastic-plastic increment stress field numerical simulation. On the whole, their direction distributions of the tectonic stress field were similar, but each unit is slightly different which varied around SEE 118°?SEE 130°. In addition, the maximum principal stress and pre-existing faults always made large influence on artificial fractures, so local maximum principal stress direction should be considered in horizontal well deployment and development work. The present tectonic stress field direction maps can provide reference for the shale gas horizontal well deployment work in Jiaoshiba area.