Research On Classification And Comprehensive Evaluation Of Tight-oil Reservoirs In Lucaogou Formation Of Jimsar Sag,Xingjiang

Tight oil is an unconventional reservoir,which is mainly developed in abnormal compact carbonate rock or clastic rock layers and has no natural productivity,but after artificial fracturing,it can often obtain industrial productivity.Tight oil is one of the most important oil and gas resources at the present stage.The dense oil of the Lucaogou formation in the Jimsar sag,Junggar basin,Xinjiang,is a typical continental dense oil in China,which is very representative.Strengthening the research and Deepening the understanding on the dense oil of the Lucaogou formation can provide support for the efficient development of the domestic tight oil.At present,the classification-evaluation of tight oil reservoirs in China has not been formed unified technical standard and method system.Through the study about the classification and comprehensive evaluation of the tight oil reservoir in the second segment of the Lucaogou formation,this paper offers a new idea for the evaluation of domestic dense oil reservoirs and enrichs our understanding of the basic theory on the continental dense oil in China.It is hoped that it can provide some reference and guidance for other related research and practice.In this paper,the relevant physicochemistry,technology and methods of the evaluation of the tight oil reservoir nowadays are investigated in detail,then the data about the tight oil of the Lucaogou group are collected and arranged carefully.It is suggested that the tight oil of the Lucaogou formation is characterized by complex and changeable lithology,high viscosity,low fluidity and the source and the reservoir develop into one layer.Based on the summary and analysis of the characteristics of tight oil reservoirs in the study area,the main controlling factors for the development of tight oil effective reservoirs in Lu-two-section of the study area are identified as five types: lithology,physical property,oil-bearing property,brittleness and source rock characteristics.On the basis of confirmed main controlling factors of effective reservoirs of tight oil and combined with existing geological data in the study area,the reservoir is classified from these six aspects: lithology,physical property,oil-bearing property,brittleness,hydrocarbon source rock characteristics and source-reservoir configuration,then the effective reservoir is devided into three types in detail: type I reservoir that its lithology is dominated by cloud-siltstone,mainly for siltstone facies,and its porosity in physical property is generally greater than 12%,the grade of oil-bearing is usually kept in oil-containing or oil-immersion,source rocks and reservoirs are mostly located in the type of source-inner,high quality reservoirs are sandwiched between high quality source rocks from upper and lower in vertically;type II reservoir that its lithology is mostly composed of sandy-dolomite and argillite-dolomite,mainly for dolomite facies,the range of porosity distribution is 5%? 12%,the grade of oiliness is mainly oil-spot and oil-trace,hydrocarbon source rocks and reservoirs are mainly of source-inner type or source-upper type;type III reservoir that its lithology is pelitic siltstone mainly,with porosity less than 5%,oil-bearing property is based on oil-trace and fluorescence,hydrocarbon source rocks and reservoirs are mostly of source-upper type or source-down type.Based on these studies,a comprehensive classification scheme for reservoir evaluation of the study area has been formed.According to the scheme,we classified and evaluated the tight oil reservoirs in the study area synthetically.The study shows that there are 2 sets of type I reservoirs,3 sets of class II reservoirs and 5 sets of class III reservoirs in the Lu-two-section,furthermore,we established the plane-distribution maps of the dominant reservoirs of tight oil in the study area,and its coincidence with existing geological knowledge is high.In this paper,a comprehensive evaluation scheme for the classification of tight oil reservoirs is formed,and the study about the comprehensive evaluation of the reservoir classification is carried out according to the plan.The results of the study are verified in some ways.