Research On The Characteristic Of Reservoir And The Rule Of Reservoir-formed In Chang 6 Oil Reservoir In Yongjing Area Of The Southern Of Zhidan Oil Field, Ordos Basin

Yongning area of the southern of Zhidan oil field is located in central and southern of the slope of shanbei, Ordos basin,the overall stratigraphy of a west dumping slope, its development of a series of low-amplitude nose-fold structures. This study aimed at the Chang6 oil reservoir in the Yanchang formation of Triassic,the use of sedimentology, petroleum geology, reservoir geology, geophysical logging, etc. theory, with a large number of logging,drilling, core logging, test oil and test-mining information, combined with a variety of testing methods and analysis tools, thoroughly and systematically studied on the area stratigraphy, tectonics, sedimentary microfacies types and distribution characteristics, reservoir characteristics. The Chang6 reservoir belongs to delta front subfacies deposition, and further divided into distributary channel, interdistributary bay, mouth dam and distal sand bar, distributary channel and mouth bar deposits composite sand body comparative development.The result shows that reservoir lithology is the main powder-fine-grained, fine-grained feldspar sandstone, minerals low maturity, the higher the maturity structure, sandstone experienced strong diagenesis, mechanical compaction, pressure solution, cementation filling, erosion, metasomatism and diagenesis of authigenic clay mineral etc. Chang-6 reservoir sandstones has reached at least the late stage of diagenesis B period; the average porosity of 10.51%, the average penetration rate of 0.49×10-3μm2, for a typical low-porosity ultra-low permeability reservoir; The pore types mainly include residual intergranular pore, secondary dissolution intergranular pore, secondary dissolution intragranular pore,moldic pore and interstitial fillings dissolution pore,middle-small pore and fine-micro throat are the main pore throat characteristics.In the comprehensive evaluation and analysis of the basis, the Chang 6 reservoir is divided into five type (Ⅱa type,Ⅱb type,Ⅲa type,Ⅲb type,Ⅳtype),Ⅱb type,Ⅲa type andⅢb type are considered as the dominated reservoirs, followed byⅡa type,Ⅳtype reservoir as non-effective reservoir.Secondly, Preliminary study the rule of Chang6 oil & gas reservoir-formed, and explicitly put forward the key control factors of oil & gas reservoir-formed:Distributary channel and mouth bar deposits composite sandstone is an important place of oil & gas accumulation; Good source-reservoir-cap combination of the configuration is oil & gas accumulation favorable conditions; low-amplitude nose-fold structures is an effective sites of oil & gas accumulation; Sandbody overlay,micro-cracks is main thoroughfare of oil & gas vertical migration.But also for the Chang 6 oil & gas reservoirs for a comprehensive and integrated analysis, pointed out that the major types of Chang-6 oil & gas reservoirs are as follows:①Up-lip pinch-out sandstone lithology reservoir;②Sandstone lenticular-body lithology reservoir;③Barrier heterogeneity lithologic reservoir;④Structure-lithology composite reservoir. Based on comprehensive study, the final,summed up and established the Chang 6 oil & gas reservoir-formed mode.