Study On Depositional Features And Hydrocarbon Accumulation Control Factors Of Jurassic In Hashan Slope Belt Of Junggar Basin

Under the guidance of theroies of sequence stratigraphy,sedimentology and hydrocarbon accumulation theory,adopting integrating macro controlled context analysis in combination with microscopic mechanism analysis,geology in combination with geophysics,based on the sequence stratigraphy and the sedimentary evolvement,this paper studied controlling sandbody model of sequence and trap forming mechanism.Combing with research on conduit frameworks,reservoir characteristics analysis and empty traps contrasted,the paper analyzed the reservoir controlling factors and built up the reservoirs forming mode,and resolved the question of hydrocarbon migration and accumulation in sloping belt of basin margin.The research result shows that there is a sedimentary evolution of the fast water invasion and multi-period shock in slope belt of basin margin of Hashan area.By the control of ancient landform,lacustrine level changes and provenance supply capacity,the four sequence models for binary system and ternary system which add up to two classes are established,which are system tracts developing completely,lacustrine transgressive system tracts suffered from erosion partly,lower system tract undergrown,high system tract suffered from erosion.Through the analysis of sedimentary facies,seven facies are identified,those are humid fan,braided river,braided river delta,fan delta,meandering river,meandering river delta and shore-shallow lake facies.And two patterns of sedimentary are built up,which are humid fan-braided river-braided river deltas in early time and river on gentle slope(including braided river and meandering river)-river(including braided river and meandering river)deltas in the middle-late time.Combinations of sedimentary systems in system tracts controlled the forming and distribution of traps in combation with unconformity.Combinations of sedimentary systems in system tracts controlled characteristics of sand bodies and reservoir-caprock association.Sand bodies of the lowstand system tracts were thick,composited into a whole-block.The lacustrine transgressive system tracts developed isolated sand bodys.Sand bodies of the highstand system tracts were relatively isolated,denuded at late stage.“Polycyclic superposition of positive sequence” sedimentary evolution process formed good reservoir-caprock association of the lowstand system tracts and lacustrine transgressive system tracts.Through core observation,elemental analysis and well logging identification,combined with analysis of influencing factors such as the original rock lithology,depositional break,paleotopography and roof lithologic character,the results showed that unconformity surface weathered crust mudstone widely developed in study area.Controlled by the two factors,it mainnly formed the trap development mode of stratigraphic-type traps in sloping belt of basin margin.It mainly formed the trap development mode of stratigraphic-type traps.The stratigraphic erosion trap,the stratigraphic-structural trap of lower system tract,and the overlap trap of high system tract are the main trap types.Through the semiquantitative and quantitive evaluation of fault translocation,it is thought that two sets of fracture systems of deep and shallow layers form the vertical migration conducting system.With the analysis of unconformity structure,it's found out that the unconformity doesn't have long transportation ability.It is cleared that carpet sand in lower system tract with good porosity and permeability form a good corss hydrocarbon carrierbed,which overlaps each other on plane,and is steady in the lateral,whose connectivity is good and thickness is great.Positive structures such as nose structure and tectonic ridges control the main migration direction of hydrocarbon,which has the ability to converge hydrocarbon obviously.The horizons cut by source-related faults and fault sealing property control the vertical distribution of hydrocarbon,and the accommodation faults in the shallow control the hydrocarbon migration in carpet sand and the hydrocarbon accumulation in sand above carpet.Lots of developing stratigraphic traps form large stratigraphic reservoirs,while lithological and structural-lithological reservoirs above carpet sand are barely developed.The hydrocarbon accumulation is controlled by the plane distribution of carpet sand and the lithology,physical characteristics and pore structures of reservoirs in different systems.At last,the model of petroleum accumulation is put forward,that is,far source hydrocarbon supplyment,fault-carpet sand translocation and four elements controlling reservoir.So it's figured out that the up-dip sandstone pinchout and isolated sand which is linked with secondary order fault are the most favorable exploration targets.