| The tectonic location of the Xiasiwan oilfield belongs to the southern part of the northern Shaanxi slope of the Ordos Basin.The main oil-bearing strata are the extension group Chang2,Chang 3,Chang 6 and Chang8 layer.The research area of this paper is the Chai Well Area of Xiasiwan Oilfield.The main research layer is the two main oil producing layers of Chang 3and Chang 6.This paper is guided by the multi-disciplinary theory of petroleum geology,using logging curves,geological logging,and filling altitude;data such as core data,thin slice identification,scanning electron microscopy,and vitrinite reflectance are used as the basis.The Chang 3 and Chang 6 reservoirs are used for stratigraphic division and contrast,structural study of sedimentary microfacies and detailed study of reservoir characteristics,providing a realistic and reliable theoretical basis for future water injection development in the study area.According to the research data,the length Chang d Chang 6 can also be divided into four groups of lengths:Chang 61,Chang 62 and Chang 63 Chang 64.After detailed reservoir subdivision comparison,the main oil layer Chang 3 is divided into two small layers of Chang31-1 and Chang 31-2,and the main oil layer Chang 62 is divided into two small layers of Chang62-1 and Chang 62-2.The source directions of the Chang 3 and Chang 6 oil layers are northeast-southwest.The Chang 3 reservoir has a relatively flat nose structure in its structure.It is the sub-facies of the delta plain.The main types of microfacies are the branch river microfacies,the onshore natural dyke microfacies,the crevasse fan microfacies,and the marsh microfacies.The branch channel microfacies are the best phase zones for sand deposits.Chang 3 is the main oil producing layer,the sand is the most developed,and the thickness changes greatly.The reservoir rock is dominated by fine-grained feldspar sandstone,and the main pore type is intergranular pore.The Chang 3 reservoir has an average porosity of 12.4%and an average permeability of 1.28mD,which belongs to the low porosity and low permeability reservoir.The Chang 3 reservoirs were classified and the results showed that the IIIb and IIa reservoirs were the most.The structural features of the Chang 6 oil-bearing strata in the study area are basically consistent with the regional tectonic features of the northern Shaanxi slope,mainly in the west-dip monoclinic form,but only locally developed with low-amplitude tectonic fluctuations sedimentary,and the reservoir genetic type is mainly an underwater distributary channel sand body.The sand body distribution is basically the same as the underwater distributary river channel,extending from the northeast-southwest direction,forming a flat strip on the plane.The thickness is 626m,and the thickness of the main channel sand body is>14m.The lithology of the Chang 6 reservoir is mainly fine-grained feldspar sandstone.The pore types are mainly intergranular pores and dissolution pores,and local microscopic cracks are developed.Reservoir heterogeneity is strong;reservoir sensitivity is moderately strong acid sensitivity,moderately weak water sensitivity,weak salt sensitivity,weak speed sensitivity,weak alkali sensitivity.The average porosity is 9.7%,the median value is 10.0%,the average porosity above the lower limit is 10.1%,the average permeability is 1.35×10-3?m2,the median value is 1.4×10-3?m2,and the average permeability is above the lower limit.1.45 x 10-3?m2.It is a special low-porosity and ultra-low-permeability reservoir,mainly composed of IIb and IIIa. |
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