Research On Sedimentary Facies And Reservoir Characteristics Of Lower And Middle Jurassic Of Bogeda Foreland Basin

The depositional system and reservoir characteristics of the Lower and Middle Jurassic in Bogeda foreland basin were analyzed by applying the techniques of provenance together with depositional system and reservoir micro-characteristics.Sediment of the Lower and Middle Jurassic was deduced to have two provenance systems which came respectively from the north Bogeda foreland and the south provenance by analyzing the heavy mineral assemblage and the distribution of heavy mineral assemblage zone. Relatively, the north provenance was a near-end provenance, and the south provenance was a far-end provenance.The distribution and evolution of sedimentary facies in Bogeda foreland basin is analyzed after dividing the type of depositional system and considering the stack style of sub-succession of strata. We can figure out the types of developed sedimentary facies in this area include braided river deltas, Fan deltas, alluvial fan, meandering river delta and lake facies.Through the sequence-tract mapping of the Lower and Middle Jurassic, the distribution and evolution of depositional systems in different periods have been revealed, including following five stage: a shadow lake-river- floodplain- marsh- shore shallow lake system of Badaowan group,a shadow lake-deltaic-floodplain-shore shallow lake system of Sangonghe group, a Fan deltas- floodplain- marsh- shore shallow lake-shallow lake of Xishanyao group, a Fan deltas(braided river deltas)- floodplain- shore shallow lake-shallow lake of Sanjianfang group, a shore lacustrine-delta- shore shallow lake group.This paper also uses lots of data of conventional rock thin sections, casting slices, scanning election micrographs, mercury injection, for discussing reservoir feathers. Reservoir rocks are mainly feldspathic litharenite, lithic arkose . Grade of maturity of rock structure and contents are low. The sandstone's cementation matter are mainly mud , carbonate etc, together with minor authigenic quartz.Dissolution pore, constricted fissure and structure fracture are the main reservoir space. Fracture is an important controlling factor for the distribution of reservoirs. The pore structure includes large hole with large throat, medium hole with medium throat, small hole with small throat and small hole with micro-throat. The result shows that there are four diagenetic events which are compaction, cementation, replacement and dissolution in Bogeda foreland basin. Since polyphase tectonic movements and long-term fault activities were experienced, faults are abundant in this sag. The Jurassic fault active period matched well with the hydrocarbon generation and expulsion periods and had an important effect on hydrocarbon migration and accumulation. Diagenetic stage is at from B period of early diagenesis to A2 period of late diagenesis. Developing degree and distribution of secondary pore are controlled by the sedimentation, the diagenesis, the tectonism and so on.Based on the synthetic analysis of sedimentation, diagenesis and reservoir properties, classification and evaluation of reservoir of Bogeda foreland basin are done. The second and the third reservoir dominate in thereservoir of Bogeda foreland basin. The Jurassic reservoirs mainly are pore- type clastic rocks with low porosity and low permeability. The structural zone of Qiquanhu, Qalekan, Shanle, Kekeya and so on have apparent good reservoir conditions horizontally. Vertically, have favorable reservoir properties and good oil-gas accumulation which can be acted as the next exploration focus.