Abstract:

The complex surface geology and intensive tectonic activities causes the poor seismic imaging in the southern fold-thrust belt,Junggar Basin,challenging structural interpretation.During the seismic interpretation of the Manas structure,we first projected the outcropped strata and faults onto the seismic lines with topographic data,then defined seismic horizons with the vertical seismic profile(VSP)and acoustic logging data of well Mana-1 and Mana-002,and finally fixed possible deep faults according to the seismic reflectance signatures.Some faults encountered during drilling can be identified by using dipmeter data.However,as chaotic seismic reflections exist in the middle-shallow layers on seismic reflection and thrust faults slipped along the shale and mudstone in the Paleogene Anjihai Formation,it is hard to identify the thrust faults in this structurally thickened formation by using dipmeter data.Correlation of seismic reflectance anomaly with fault depth in well Mana-1 and Mana-002 indicates that there is certain relationship between the thrust faults and the abnormal formation pressures tested during drilling.A series of the thrust fault points of the wells are identified by monitoring abnormal formation pressure and the pressure gradient during drilling,and they are verified by both the pressure data of wells and the fault points identified in the adjacent wells.The well formation pressure data tested with the Modular Dynamic Test(MDT)shows that two pressure systems exist in the Ziniquanzi Formation and are separate by a thrust fault.The final seismic structural interpretation demonstrates that the Horgos-Manas-Tugulu thrust belt is composed of a series of imbricate fans.

Key words: overpressure, structural modeling, formation pressure, pressure gradient, thrust, fault calibration, seismic profile interpretation, southern Junggar Basin