Study On Reservoir-forming Mechanism And Enrichment Law Of Chang 6 Reservoir In Chaishangyuan Area Of Ordos Basin

Based on the theory of modern oil and gas accumulation geology,this paper collates and analyzes core data,logging data,analytical data,production test data,production performance data and so on,by using the research methods of the combination of macro and micro,dynamic and static,exploration and development,on the premise of fully understanding the basic geological background of the study area,This paper makes an in-depth study on the reservoir-forming mechanism and enrichment law of Chang 6 reservoir of Triassic Yanchang formation in Chaishangyuan area of Qilicun Oilfield in Ordos Basin.The details are as follows:First of all,through the test data of fluid samples,it is determined that the crude oil of Chang 6 formation in the study area shows the characteristics of light oil with low viscosity,low sulfur content,low wax content and high freezing point.The type of formation water is CaCl₂.Secondly,through logging interpretation,it is known that the enrichment degree of Chang 6 reservoir in the area is different,which is mainly enriched in Chang 6₁⁴ and Chang 6₂²layers longitudinally,and is distributed in a large area on the plane,showing the characteristics of cluster"quasi-continuous"distribution as a whole.The water layer is sporadically distributed in the area,and the south is the main high-yield water area.In addition,the oil moisture of Chang 6 reservoir in the area is not complete,there is no obvious oil-water interface,and there is no edge and bottom water,so it is determined to be a typical tight lithologic reservoir.At the same time,core observation and microscopic observation show that fractures are an important channel of crude oil migration in the area.combined with geochemical test and analysis,it is determined that the crude oil in the area is mainly vertical migration.Furthermore,the reservoir-forming mechanism can be summarized as follows:under the action of hydrocarbon generation and pressurization,the crude oil generated by local source rocks moves vertically to the overlying Chang 6 tight reservoir through macro and micro fractures and longitudinally superimposed permeable sand body.when it encounters a caprock with certain shielding conditions,it will accumulate and form a reservoir,which is a typical lower-upper reservoir-forming model.are similar,the better a single factor is,the more conducive to reservoir enrichment.In addition,according to the correlation between production performance data and reservoir-forming factors,it is known that the degree of reservoir formation and enrichment in this area is controlled by four factors:hydrocarbon source,reservoir,transport conditions and caprock conditions.The controlling effect of various factors on reservoir distribution is enhanced in turn.According to the quality of hydrocarbon source conditions,the enrichment law can be divided into eastern and western regions.Where the hydrocarbon source is poor in the east,the crude oil is more enriched in the lower strata with better reservoir development and less in the upper strata,while in the west,the hydrocarbon source is more favorable,and the enrichment of crude oil is more controlled by transport conditions and caprock conditions.in the case of the same degree of reservoir development,the coupling relationship between transport conditions and caprock conditions is more beneficial,the more conducive to crude oil enrichment.In addition,when other reservoir-forming factors are similar,the better a single factor is,the more conducive to reservoir enrichment.Finally,on this basis,the"Sweet Spot"of Chang 6 reservoir group in the study area is divided into three grades.The lower limit of reservoir forming condition of each grade"Sweet Spot"is determined,and the weight calculation formula of each factor is introduced to calculate the value of monolayer comprehensive index"F".According to the relative value of"F",the"Sweet Spot"of non-main layer is predicted.