The Research On The Geologic Characteristic Of Yan-8 Reservoir Of Yanwu Oilfield In X Area,ordos Basin

The X area of the study area which belongs to the northwestern part of the Zhenyuan area,is located in the southern part of the Tianhuan Depression in the Ordos Basin.The Yan 8 layer of the Jurassic Yan'an Formation is an important layer for the development of the X area.However,there is no comprehensive understanding of the geological characteristics due to the complex river-crossing and accumulation rules of the Yan 8 layer,which seriously affects the development progress in the study area.To provide solid geological basis for the efficient,reasonable and scientific development and exploitation of the target interval in the study area,the factors affecting the oil-bearing property of Yan'an 8 reservoir were studied comprehensively.Mud logging data,logging data,drilling data,oil testing and various testing data werre used to analyze the tectonic structure and sedimentary microfacies.The distribution of sand bodies and characteristics of the reservoir of the Yan'an formation were studied in the X area.It can be concluded that:1)the Yan 8 reservoir in the study area is divided into two small layers.The tectonic structure has strong inheritance and itis characterized by the development of a northwest-southeastern anticline,with multiple northeast-southwestern rhinozoic structures and a small secondary anticline developed on it.2)the Yan 8 period belongs to the braided river delta plain sedimentary system,which controlled by the provenance in the southwest direction.Microfacies mainly contains distributary channels,interdistributary depressions and marsh.There are 2 to 4 southwest-northeast distributary channel sands body developed in the study area.3)the rock types in the reservoir are mainly detrital quartz sandstone with medium-coarse grain size.The interstitial mainly includes illite and iron calcite,with a content of 5.0%.4)the main pore types are intergranular pores and feldspar dissolved pores.Reduced-diameter throat and curved larynx are the main throat types of channels.The reservoir has a good overall pore-throat structure.Porosity of the reservoir is between 12%to 18%,and its permeability is between 10×10^-3?m² to 1000×10^-3?m².The reservoir belongs to medium-low porosity and medium permeability reservoirs.5)the diagenetic evolution stage of the reservoir is in the mid-diagenetic stage A due to the impact of mechanical compaction,pressure dissolution,cementation and dissolution.6)the water flooding displacement method is mainly network displacement.The overall displacement efficiency is relatively high.7)the reservoir has a low heterogeneity.Reservoir in the study area is divided into three types.It is considered that Class I and Class II reservoirs are the most developed.These two types are mostly distributed at the center of distributary channels.Class III reservoirs are relatively undeveloped in the study area.The main controlling factors of oil-bearing property of Yan 8 reservoir in the study area is structure and sedimentary facies.The remaining control factors include sand body distribution,reservoir physical properties and diagenesis,etc.It is considered that Yan 8 reservoir in X area is lithology-structure reservoir and it has a wide overall distribution range.To increase total oilfield production,five Class I favorable production areas with a total area of 0.4km²,and two Class II advantageous production areas with a total area of 0.11km² are selected for deploying wells according to the oil-bearing control factors and reservoir types in the study area,.