| The Gaotaizi oil layer in the Longhupao-Qijia area in the northern Songliao Basin is rich in tight oil resources.The microstructural characteristics are the focus of research on tight oil reservoirs,and also an important factor affecting the distribution of macroscopic oil and water and the oil content in the production fluid of tight oil development.The purpose of this study is to analyze the influencing factors of macro oil-water distribution differences from the microstructure and accumulation mechanism of tight reservoirs.This paper intensively studied the lithology,physical properties,oil-bearing properties,pore types and microscopic pore-throat structures,major diagenesis and diagenetic evolution sequences of the tight reservoirs in the Gaotaizi oil reservoir in the Longhupao-Qijia area are studied in depth.,basing on a large number of core observations,thin slice identification,cathodoluminescence,scanning electron microscopy（SEM）,porosity and permeability test,full rock and clay mineral relative content test（XRD）,nitrogen gas adsorption（N2GA）,mercury intrusion porosimetry（MIP）and rate-controlled mercury（RCP）,micro CT,nuclear magnetic resonance（NMR）,fluid inclusion microthermometry and fluorescence spectra.The upper and lower limits of the physical properties of tight reservoirs is accurately determined and a set of multi-parameter dense reservoir classification evaluation criteria is established.The coupling relationship between the reservoiring period and the reservoir compaction period is analyzed,and the coupling relationship between the reservoiring period and the reservoir compaction period is analyzed to control the macroscopic oil-water distribution.Based on the nuclear magnetic-fluorine oil flooding formation water experiment,the reasons for the difference in oil content in the production fluid of different tight oil areas during development were analyzed from the microscopic point of view.Research indicates:1.The rock type is dominated by lithic feldspar sandstone and feldspathic lithic sandstone.The highest feldspar content,followed by quartz.Clay mineral content exceeds 10%.The clay minerals are mainly composed of illite,chlorite and illite/smectite formation,and the interstitial is mainly composed of carbonate cement and mud filling.The porosity distribution ranged from4.4%to 20.81%with an average of 11.35%.The permeability ranged from 0.02×10-3μm2 to84.46×10-3μm2 with an average of 8.40×10-3μm2.The study area mainly includes four types of reservoir spaces:intergranular pores,dissolution pores,intergranular pores of clay minerals and micro-cracks.2.The microscopic pore structure characteristics of tight reservoirs in the study area were analyzed by using N2GA,MIP,RCP,micro CT,NMR experiments.The pore size distribution in North of Qijia is 2.5nm～100μm,in South of Qijia is 2nm～50μm,and in Longhupao is2nm～20μm.Reservoir quality is simultaneously controlled by sedimentary microfacies and horizons.3.The upper and lower limits of tight oil reservoirs were determined according to the mechanical equilibriμm method,reservoir type analysis method,water film thickness method,empirical statistics method and constant velocity mercury intrusion method.According to the mercury inflection point theory method,energy storage parameter method,pore throat structure parameter method and N2GA method,the tight oil reservoir is divided into five levels:conventional,class I,class II,class III and class IV tight reservoirs.At the same time,the classification evaluation criteria are established based on the logging characteristic parameters,which provide a basis of macro-level evaluation for reservoirs.4.The Gaotaizi tight oil layer experienced three oil and gas fillings,and the two phases of oil and gas accumulation were the end of the Nenjiang Formation and the Sifangtaizi-Mingshui Formation.The macro-oil-water distribution differences in North of Qijia,South of Qijia and Longhupao areas are controlled by the reservoir compaction period-accumulation period coupling relationship type.The difference in oil content in the production fluid between the test area and the outer expansion area is controlled by the original oil saturation and the microscopic pore throat structure of the reservoir. |
