Research Of Structure Characteristics And Which Control On Hydrocarbon Accumulation In Chishui Area,Southeast Sichuan Basin

On the basis of previous studies,this paper by using the seismic profile combined with drilling data and equilibrium profile method to get qualitative and quantitative analysis the structural and evolutionary characteristics in Chishui area,Southeast of Sichuan basin.At the same time,make use of the structural sand box experiment to discuss the control factors and the dynamic process of the two sets of formation which are separated by detachment layer,and to analyze how the structural movemments influence the preservation of oil and gas reservoirs in deep and ultra-deep beds,then that can provide theoretical basis for deep hydrocarbon accumulation in Southeast of Sichuan basin.The overall structures strength is weaken from the outside of the basin to the inside in the study area.The current two groups of structural features are formed by SE-NW and SW-NE directions superposed stress field,it is show that the structure deformation and evolution in this area are mainly controlled by the detachment layer in upper-middle Cambrian gypsum salt rocks,this is why above and under the detachment layer is different structural deformation styles.formed by detachment layer Above the detachment layer,structure was formed later and the deformation is strong,the geometric shape of folds were controlled by the large thrust faults which are development at the core or flanks,and the decollement layer is thicker in the anticlinal core but thinner to the flanks,the downward faults terminated in the slip zone;while under the detachment layer,structural is stable and the deformation strength is weak,there are only some small local uplifts.The shortening of the displacement of the upper layers are 6.4-10 times than that under the slip layer,performed as the composite structure of fault-related folds,so that the deformation degree and deformation characteristics are not only controlled by the slip layer,but also related to the deformation velocity.The sand-box experiment shows these above results either.Consequently,the upper-middle Cambrian decollement layer,as the oldest and the largest thickness of detachment layer,has a direct impact on the formation and evolution of several faults,to change of the folds and the formation of the double structural styles in Ximen region,in Chishui area,Southeast of Sichuan basin.According to the degree of regional compression and the distribution of slip layer,this paper divide the structures what influence the preservation condition of oil and gas into three zones:(1)Orogenic belt to basin margin strong deformation zone;(2)Edge of the basin to the strong deformation zone in the northeastern part of Southeast Sichuan;(3)Margin of the basin to the weak deformation belt in Chishui area,southeast of Sichuan basin.The condition of early tectonic preservation is better in Southeast of Sichuan basin,it is inferred that the accumulation of oil and gas has go through the following stages: paleo oil reservoirs are formed in Permian to Triassic period,paleo gas reservoirs are formed in Triassic to Jurassic period,adjustment and destruction of paleo gas reservoirs in late Cretaceous.In strong to moderate deformation zone,the preservation condition is getting worse,so that oil and gas can escape directly through the fault or laterally migrated.But in the weak deformation zone,the traps can preserved in beds under the slip layer,lateral and vertical preservation conditions are better than those in other areas,which have good exploration prospects.