The Reservoir Characteristics And Control Factors Of Oil Of Chang4+5of Western Nanliang Area

Western Nanliang area is an important oil-producing region in the Ordos basin, triassic Yanchang formation is its main oil-bearing series, Chang3, Chang4+5, Chang6, Chang8of Yanchang and Yan10of the Yan’an oil layer developed well in this area. Compared to other layers of research area, the Chang4+5is a new formation of the new block, the basic research of which is weak. In order to identify the regulation of oil and gas accumulation in this area, it is necessary to study the geological characteristic and controlling oil-bearing factors profoundly.Based on the theoretic knowledge of modern sedimentology, reservoir geology and lithofacies paleography, the research on the structure, stratigraphy, sedimentation, reservoir and oiliness characteristics of chang4+5is conducted in this paper with adapting enormous tests and analysises.On basis of those, the distribution of quality reservoir section in the plane and vertical oily controlling factors and the next step scroll through the expansion of the edge direction of the regional development are summarized in this paper.The structure of the Chang4+5reservoir is dumping in the west on the background of the monoclinic forming a four-relief, low-amplitude structural nose and six micro-nose long construct developing the delta front depositional systems. Due to the influence of compaction and cementation, the district develops low porosity and low permeability reservoirs. Because of late dissolution in some areas, the porosity of this reservoir is expanded, which improves the reservoir permeability, and makes some of the relatively low permeability sandstone with better reservoir properties.The various parameters of Chang4+5reservoir are clustered analysis divided into three categories. Oil and gas gathered in the reservoir of Class I and Class II Due to poor physical properties of the Class III reservoir oil and gas are difficult to gather at a large scale. Class I reservoir generally distributes in the thick sand body and better continuity distributor channel microfacies; Class II reservoir mostly distributes in parts of rivers or river flank which is the barrier and interbed development phase with strong heterogeneity; Class III reservoir distribues in the thin sand body deposition and close to the interdistributory. Comprehensive analysis determines the study area next to scroll the expansion side of the direction of the north-east, north and southern regions. It provides a reliable basis for future exploration and development. After comprehensive analysis of the distribution characteristics of Chang4+5reservoir sedimentary microfacies, sand body distribution, properties, etc. combining with the core observation, casting thin sections, cathodoluminescence, mercury-injection, relative permeability and testing data, the results show that Western Nanliang area reservoir oil-bearing properties are mainly controlled by the deposition, physical properties, diagenesis, reservoir heterogeneity, reservoir-cap assemblage characteristics and hydrocarbon migration. The uplift of some areas of the nose may to some extent control the oil bearing property.