Tentonic Characteristics And Oil-gas Accumulation Study Of Qijiang District In Sichuan Basin

The Southeast Area of Sichuan has experienced exploration and developmentmore than50years, with major oil and gas layers of Permian system and Triassicsystem. Now it comes to its later period. Favorable exploration blocks knownaccording to anticline reservoir forming theory are fewer and fewer, however, thereare much potential resource. This thesis traverses into the key exploration targets insoutheast of Qijiang District in Sichuan Basin: permian system--ChangxingFormation and triassic system--Feixianguan Formation, studying its tentoniccharacteristics, tectonic evolution and ancient landform. This thesis takes structuralgeology theory and methods and combines predecessors’ research results from theperspective of tectonic characteristics. It summarizes how the tectonic characterscontrol the oil and gas reservoir in this region. My comprehension through this studyare:(1) Conducting level calibration by the record synthesis of2d seismic survey line.Precisely explaining the seven reflecting interfaces: Changxing group bottom margin(Tp2ch), the set of Feixianguan bottom margin (TT1f1), the three sections ofFeixianguan bottom margin (TT1f3), Jialing River group bottom margin (TT1j1), thethree sections of Jialing bottom margin (TT1j3), the Xujia River group bottom (TT3x),the Jurassic bottom (TTJ1z). According to the comparison of synthetic record,Changxing group reflection is form by two median-strong phases and the energy ofreflection wave changes little. Feixianguan bottom margin is a lineup with strongerenergy and better continuity. Jialing River group bottom margin is a median-strongreflection and its continuity is relatively good. The three sections of Jialing bottommargin is the character of intermittent weak amplitude, median amplitude seismicresponse. Xujia River group bottom mainly manifests its two continuous strong phase.Pearl restructuring bottom side is formed by the reflection wave of two median-strongphases, having continuous pro-strong phases.Through the structure compilation of Changxing group bottom, Feixianguan groupbottom, Jialing River group bottom, and comparison-analysis of the these characters,conclusions are reached as follows: the fault structure of Sichuan southeast region distributes in NEE--SWW direction with smaller scale, while in NNW--SSE directionwith larger scale. In the middle of study area, the structural configuration are in goodconsistency from late permian epoch to orogenic permian epoch--the middle partstays in the low area of the structure while the periphery stays in a higher situation.From studying tectonic evolution of the research area, it shows that in the workingarea, the tectonic deformation of NE--SW direction is gentle, with fault developspartially. In the direction of NW--SE, the structural effect is strong. Before the upperpermian series’ deposition, the earth crust began uplifting and a few faults aredeveloping with unapparent folds or transformation in stratum. Before the triassicsystem Feixianguan group had its deposition, the overall structural appearance has nosignificant change. Faults increasing slightly before triassic system Jialing Rivergroup had its deposition, reflecting the continuous enhancement of slight folddeformation. Before triassic system Xujia River had its deposition, the fault had gotthe succession character, changing from early normal fault properties to reverse fault;and also the stratum deformed to some degree. The Jurassic sedimentary pro-fault hasdeveloped remarkably, along with tectonic compression deformation. Rocks fracture,forming new faults, and later under the influence of Himalayan movement, theresearch area happens overall folds and transformation. Early stratum is uplift anddenuded, forming current tectonic appearance.Making use of strata thickness flip, the ancient landform study shows, the ancientlandform of research area experienced the evolution process as follow: beforeChangxing group depositon, the south-west is high and the north-east is low; beforeFeixianguan deposition, the periphery is high and the middle is low but the differenceis not great; during the period of Jialing River group the ancient landformcomparatively flat. To sum up, in the above three stages, ancient landform changesgently and tectonic movement has little influence on it.Through study on generation, containing and covering conditions in the researcharea, this thesis analyzes the relationship between tectonism and oil/gasmigration-accumulation in this region, especially local structure’s control action on oilgas. There are mainly four aspects:1. Tectonic evolutionary phase’s control on oil gas;2. The relationship between Luzhou Palaeohigh and oil gas;3. The relationshipbetween superposition of structures and oil gas;4. The control action on oil gasimposed by fault and plane of unconformity.