Research On The Genetic Mechanism And Reservoir Fluid Identification Of Low-resistance Gas Layers In The Ziniquanzi Formation In The Southern Margin Of The Junggar Basin

In this paper,the low-resistivity gas layer of Plaeogene Ziniquanzi Formation in the southern margin of the Junggar Basin is taken as the researchtarget.Based on the well logs and petrophysical experiments in the study areas,the paper studies the problem of the genetic mechanism,the fluid identification,and well logging interpretation model in the low-resistivity reservoir.The research on the reservoir characteristics and four-property relationship shows that the reservoir has the fine lithology and high shale content,and porosity and permeability has a good relationship with the particle size of the rock.The macroscopic genetic mechanisms of the low-resistivity gas layer are jointly contributed by the geologic structure and sedimentary characteristics in the study area.The geologic structure provides a basis for the reservoir of low resistivity,but not a main controlling factor.Although the construction amplitude is sufficient to provide the displacement pressure,the overall resistivity is still high in the lower part and lower in the upper part.The delta front sediment as the dominant sedimentary facies causes the fine lithology,high shale content,and complex pore structure of the reservoir.The microscopical genetic mechanisms of the lowresistivity gas layer are jointly affected by the high cation additional conduction and high bound water saturation.High cation additional conduction is mainly caused by the clay with cation exchange capacity higher than that in other oil fields.Thus,the high cation additional conduction is the main cause of the low-resistivity.The fine particle size,high shale content,and clay type lead to a complex pore structure and enventualy results in the high bound water saturation.So,the high bound water saturation is also the main cause of the low-resistivity.The conductive minerals and formation-water saninity are sub-controling factors.In engineering,according to the double lateral time-lapse logs,the intrusion of drilling fluid into the formation will further reduce the measured resistivity.Therefore,it is also an important cause.Based on the analysis of the genetic mechanism of low-resistivity,the cross plots of the Rt-AC,Rt-DEN,and Rt-CNL based on sedimentary facies,Rwa(Rt)-?SP,Rwa(Rt)-??,and moveable water analysis method are slected to identify the fluid property,which achieves good application results.Finally,we introduce the low-resistivity quantitative interpretation models for calculating the shale content,porosity,permeability,water saturation,and bound water saturation.The water saturation model includes variable parameter Archie model and Waxman-Smits model,and the determination of relevant parameters in the model is described in detail.Through the above research,this study clarifies the low-resistivity genetic mechanism and proposes the fluid-identification method which proves to be effective in the field applications.Overall,the study provides a reference for well logging interpretation and evaluation of lowresistivity gas layer.