| This paper is focused on the characteristic of deep geostress field and rock burstin,the second member of the Upper Triassic Xujiahe Formation inXinchang area, of Western Sichuan depression. According to the formation lithology,geological structure and geological evolution in Xinchang and adjacent area,geological model has been set up through investigating the drill cores from deep rock masses and the comparative study among the materials of mud logging,well loggingand well completion. Then analyzingthecharacteristicsof geostress field in the study area and predicting the features of the structure plane and the distribution rules of deep rock masses by systemicengineering geology and structural geology methods. According to the study,several conclusions can be drawn as follows:(1)The stratum in the second member of Xujiahe Formationin study area has experienced 5 large-scale tectonic movements : the middle stage of Indosinian movement(Anshan movement), the middle stage of Indosinian movement ~ the latestage of Indosinian movement,the early stage ofYenshan movement~the middle stage ofYenshan movement,the late stage ofYenshan movement~the middle stage ofHimalayan movement,Himalayan movement.(2)Combined traditional structural geological methods with modern rock mechanical methods, geostressmeasurement methods, large-scale physical simulationand numerical simulation methods,a systemic methods about the analysis of deep geostress field and the prediction and evaluation of fracture has been set up(3)According to the field investigation,logging curve,image loggingand the analysis of borehole cores in the second member of Upper Triassic Xujiahe Formationin study area,the fracture distributing in study area are mainly small angle cracks and including some oblique cracks,high angle crack and meshy cracks. The strike directionsof main cracksare NEE,NE,SEE.(4)Through multi-periodKaiser test,a preliminary methods that acquire ancientgeostress has been set up. The data showed that the stratums in study area had experienced at least four phases of tectonic movements(5)According to the uniaxial test and triaxial test in laboratory, the physical mechanics parameters have been obtained and statisticalanalyzed.(6)The study area has flat terrain and the fault structures control the distribution of geostress field. In such three stratums,the geostress field presents discontinuity and the concentration of maximum principal stress and shear stress in the ends and turning parts of faults. And the two sides of fault shows stress dissipation and the minor principal stress appear to be tensile stress. From the view of longitudinal profile,the geostress field is obvious zonal:The geostress field of the stratums that above Qianfoya stratums are continuous distribution and the maximum principal stress is nearly horizontal. Affected by faults,the direction of principal stress in Xujiahe Formation is different from parts,especially around the faults,where the geostress field is discontinuous and the direction of principal stress is fickle. The geostress field of the stratums that at the bottom of Xujiahe Formation is continuous distribution and most of the maximum principal stress turn vertical.(7)According to the result of three-dimensional physical simulation and numerical simulation,combined with the core observation and log analysis,the paper determined the standard for prediction and predicted the development characteristics of fractures for three stratums. The results showed that the fractures mainly developed near the fault zone,turning parts of steep flank and culmination in the 7th,4th and 2th of sandstone stratums of the second member of Xujiahe Formation. The strike direction of fractures appears to be NE,SN,NW and EW. Most of them were low-angle shear fractures, while there were also some tension fissures in the culmination. |
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