Logging Evaluation Method For Low Resistivity Reservoirs In The Chang 4+5 Reservoir Of X Oilfield In Ordos Basin

X oil field is located in the south-west of Ordos Basin, of which section Chang 4+5 member reservoir is a low resistivity one and its characteristics of low-resistivity leading some difficulty to log response and explanation. Based on the origin analysis of the low resistivity reservoir, this paper studies logging recognition method of the low resistivity reservoir in studied area, which provides evidence to logging interpretation method of the low resistivity reservoir in studied area.According to the characteristics of low resistivity reservoir in studied area, this paper launches a series of research. Firstly, according to the basic geological data, core data and logging data of the studied area, the four properties' relations of oil reservoir in studied area are researched, and the result shows lithology, physical properties, electrical property, oiliness of the reservoir as well as the integrated relations of them. Secondly, this paper analyses the origin of the low resistivity reservoir in studied area, including lithology, clay mineral, high irreducible water saturation, pore structure, formation water salinity, among which clay mineral and formation water salinity are the main factors. Based on origin analysis of the low resistivity reservoir, qualitative identification of low resistivity reservoir in studied area is conducted, for the limitation of the research data, this paper identifies the low resistivity reservoir in studied area by using the ratio of relative spontaneous potential and mud resistivity, apparent spontaneous potential and the crossplot of Acoustic and resistivity, the former two methods achieve good results. Finally, this paper conducts quantitative evaluation on the low resistivity reservoir in studied area. And the models of shale content, porosity, permeability and oil saturation are established respectively. But due to the characteristics of high gamma of reservoir in the studied area, the crossplot of Neutron and Density and several kinds of logging data are chosen to calculate the minimum of shale content, the results show that the later has good application effect.According to the study above, this paper obtains a set of research methods of logging recognition and quantitative evaluation that can be well applied to the studied area, these methods also achieve good results in practice, which provides reference to logging interpretation in the oil field.