Zichang Oilfield Drop Ditch - Shek Home Laozhuang Mayor 2 Reservoir Characteristics And Hydrocarbon Enrichment Patterns

Zichang oil field is located in Shanbei slope of the south Ordos Basin. The Chang-2 oil-bearing beds is the main bed producing oil. According to the characters of lithology, electricity and oiliness, the Chang-2 oil-bearing beds is subdivided into Chang-2 , Chang-2 and Chang-23. And the time correlation in sequence stratigraphic unit was realized according to the temporal rock maker.According to the analysis of the facies marks, such as petrosal kinds with the features, sedimentary structure, fossils, logging facies and other criteria in the study area, the analysis of the facies shows that the Chang-2 oil-bearing beds is a delta plain sedimentary system. On the basis of area geological background, the distribution pattern of sedimentary microfacies in the Chang-2 oil-bearing beds is distinguished by the analysis of geology facies, logging facies, sandstone thickness and sandstone percent and other sedimentary character.Based on all the study, we conclude that: the reservoir sandstone is fine-graded felsipathic sandstones and the reservoir sandstone has reached the late diagenesis A period in the study area. In generally speaking, the reservoir is one with low pore extra low permeability. The porosity is mainly the kind of intergranular pore, especially the kind with small-middle or middle pore and big pore. The research on unhomogeneity of reservoir also shows the homogenenity is stronger in each stratum than it between two strata. Analyzing the controlling factors to reservoir, the result shows that sedimentary microfacies and diagenesis are the main factors of controlling and affecting distribution of reservoir in study area.The result of the analysis on natures of oil, water and so on, shows the oil of Chang-2 oil-bearing beds in the area belongs to conventional oil which shows terrestrial facies with low density, low viscosity, low freezing point and low sulfur content. And the kind of formation water in the study area belongs to calcium chloride(CaCl2). The total saltiness of formation water is comparatively high. The sandstones of reservoir act as slightly water-wet. The kind of trap is lithologic and structural trap belonging to normal temperature and low pressure system with theelastic-soluble gas driving oil.The research also obtains enrichment characteristics of the Chang-2 reservoirs. It shows that the study reservoir is controlled by delta plain distributary river where is considered as the most important deposit areas. The fine regional cap formation also supply the good barrier conditions. And the nose structures and the microfissures help the deposit as well.According to the kinds and distribution on space of the trap,and combined with the reviewing studies,the research concludes that there are two entrapment models,one is the sandstone updip wedge-out reservoir. The other is the structures -litjology models mathed by culmination of nose and sandstones.