Optimization Of Logging Saturation Interpretation Model Under The Constraint Of Reservoir Conditions

The Chang 6 reservoir in the Triassic Yanchang Formation in the Ordos Basin is a typical tight sandstone reservoir with huge proven oil reserves.It is the most important oil-bearing layer in the Yanchang Formation.The reservoir conditions such as source rock,accumulation dynamics,reservoir and their matching relationship determine the reservoir distribution and oil and gas enrichment.The study of oil bearing in reservoir is always an important and difficult problem.At present,most of the oil-bearing logging evaluation methods only consider the geological characteristics of reservoir,and do not take the heterogeneity of source rock,reservoir and accumulation dynamic as constraint conditions.Then,the logging interpretation parameters are selected by classification and the logging interpretation model is established under the different reservoir conditions match types.In order to accurately evaluate the oil-bearing property of the reservoir,on the basis of clarifying the source rocks,sedimentary microfacies,reservoirs,and accumulation dynamics,with the geological parameters of the reservoir conditions as constraints,determine the matching type of the reservoir conditions,and carry out evaluation of reservoir geological characteristics by using logging data.Furthermore,the oil-bearing logging evaluation method of the reservoir is optimized,and the lower limit of the reservoir parameter is determined.In the study of reservoir geological conditions and oil-bearing main controlling factors,the comprehensive quality and spatial distribution of source rocks are analyzed based on the research of source rocks in Chang 7 member.The source rocks of Chang 7 member in the study area can be divided into three types:bottom-developing type,interbedded type and top-developing type.The source rocks have high hydrocarbon generation conversion and hydrocarbon generation intensity,which are good source rocks and conducive to the formation of oil reservoirs.Based on core observation and other data,it is determined that chang 6 member of the study area belongs to delta front sedimentary subfacies,with three types of continuous superposition type,interval superposition type and isolated type sand bodies,and the macroscopic sand body has strong heterogeneity.According to core observation,thin section analysis,scanning electron microscopy,nuclear magnetic resonance,high-pressure mercury injection and CT scanning,the chang 6 reservoir is dominated by dissolution pores and intergranular pores,followed by micropores and intergranular pores,with four types of pore structures and four types of petrophysical facies combinations.The distribution of reservoir in Chang 6 member is controlled by source rock,accumulation dynamics,reservoir and their matching relationship.On the basis of experimental analysis and comprehensive study of reservoir geological conditions,the logging parameters are calibrated with experimental data,reservoir condition logging evaluation is carried out,and reservoir condition matching types are accurately divided.Using conventional logging parameter overlap graph,Δlog R and multi-parameter regression method,a logging model for identifying and evaluating source rocks in Chang 7member was established.Using conventional logging parameters and experimental analysis data,the hydrocarbon generation intensity of source rock is calculated quantitatively and the quantitative evaluation of source rock is realized.The natural gamma method,the compensated neutron-density method,and the spontaneous potential indicator method were used to quantitatively calculate the shale content of the Chang 6 member,and the multi-parameter regression of reservoir porosity and the calculation model of formation factors were established;the empirical statistical method,Kozeny-Carman Model,stepwise regression model,and nuclear magnetic resonance method are used to calculate reservoir permeability.By combining conventional logging data with imaging logging and experimental analysis data,a logging evaluation model of reservoir microscopic pore structure is established to realize comprehensive evaluation of reservoir quality.Under the constraints of source rock,accumulation force,source-reservoir distance and reservoir parameters,six matching types are divided.They are respectively"high quality source rock-strong accumulation power-high quality reservoir"（ⅠA）,"high quality source rock-strong accumulation power-medium or poor reservoir"（ⅠB）,"medium source rock-medium accumulation power-high quality reservoir"（ⅡA）,and"Medium source rock-medium accumulation power-medium or poor reservoir"（ⅡB）."Poor source rock-weak accumulation drive-high quality reservoir"（ⅢA）,"poor source rock-weak accumulation drive-medium or poor reservoir"（ⅢB）.Reservoir fluid identification methods were established,including overlapping graph,double coefficient crossplot,pore structure exponential resistivity crossplot,Rt-CDI crossplot,movable water analysis,array induction gradient factor and Fisher discriminant.The logging interpretation parameters are determined by classification,and the reservoir saturation calculation models suitable for different reservoir conditions are selected to improve the accuracy of logging interpretation.The lower limits of reservoir physical properties corresponding to different reservoir condition matching types were determined by statistical method of oil test,mercury-injection experiment and reservoir forming dynamic method.The lower limits of porosity and permeability corresponding to high charging mode under high quality source rock-strong reservoir forming dynamic condition were 6.0%and 0.06×10^-3μm²,respectively.The lower limit of porosity and permeability corresponding to normal charging mode under medium source rock-medium accumulation dynamic condition are 7.5%and 0.10×10^-3μm²,respectively.The lower limit of porosity and permeability is 8.3%and 0.13×10^-3μm² for the low charging mode under the condition of poor source rock and weak accumulation dynamic.