Research On Sedimentary Characteristics Of Chang 3 Oil-bearing Formation In Zhenbei-Yanwu Area

The sand body of Chang 3 oil bearing formation is developing in Zhenbei YanwuArea of Ordos Basin, which can be important replacement strata in the followingevaluation exploration of oil and gas in this area. So far, there is no further study on thereservoir forming rule of oil and gas and sedimentary system of Chang 3 oil bearingformation in this area.Using logging, coring, integrated logging and geo chemical data, the author studiesthe provenance, sedimentary characteristics and reservoir forming factors of Chang 3oil bearing formation in Zhenbei Yanwu Area in Ordos Basin, through the basic theories ofSedimentology and Petroleum Geology. The controlling factors of the reservoir formingare expounded preliminarily, while favorable targets are also predicated in this dissertation.The results show that the sedimentary sources of Chang 3 oil bearing formation inZhenbei Yanwu Area mainly come from Qinling orogeny belt and thrust fold belt of eastQilian mountain on the Southwestern Margin of Ordos Basin. The direction of source isfrom southwest to northeast. In Chang 3 Period, the study area mainly developed thesedimentary system of the meandering river delta, which can be divided into the delta plainsubfacies and the delta frontal subfacies. On the plane, the above subfacies can be dividedinto distributary channel, inter channel depressions, subaqueous distributary channel andinter channel bays. In which, the channels occupy 33%~37% of research region, and thedistribution of sandbodies are controlled by the trend of river channels. The porosity ofChang 3 reservoir ranges from 7% to 15%, which is low porosity and low permeabilityreservoir, and the permeability is general 0.01～6×10 3 m2. The stage of diagenesis is atthe early period of mature sub member of middle diagenetic stage. The type of Chang 3reservoir can be divided into type I, type II, type III and type IV. The structure condition of the study area is relatively simple, which is generally east high and west low west dippingmonocline. On this basis, it is extruded by stress of compression at NS direction anddifferential compaction to form a series of nose structures, which is wide and gentle as wellas low amplitude. Hydrocarbon distribution of Chang 3 mainly is controlled by suchfactors as the sedimentary micro facies,structure and physical properties, and thestructural lithologic trap is favorable for hydrocarbon accumulation.According to the above study, multiple favorable areas of the major target layer inChang 32 member are predicated. And the favorable exploration areas of Chang 3oil bearing formation can be divided into three grades: the favorable area in Grade I isZhen 83 well area of Chang 32 member; and the favorable areas in Grade II major in sixareas, including Xi 115 well area of Chang 32 member; while, the favorable areas in GradeIII include the northeast section of Mu 9 well and the northeast section of Zhen 235 well ofChang 32 member. The data laid the foundations for further study.