Research On Tight Oil Reservoirs Geological Evaluation And Classification Of The Chang7 Member In Southern Ordos Basin

With the development of global oil and gas consumption continues to grow,the developing potency dimension of conventional oil and gas resources continue to increase,the conventional oil and gas reserves significantly smaller,as the replacement area of conventional oil and gas resources,unconventional oil and gas resources gradually aroused people's attention.There is abundant tight oil rescource in Ordos basin,where the reservoir scale is large and the oil filling degree is high,but the reservoir there belongs to tight reservoir with complex reservoir pore structure,strong heterogeneity and complex relationship between oil and water seepage,only a few of the oil can be developed,which restricts the efficient development of tight oil resources seriously in the basin.Therefore,the research was aimed at the Chang7 tight oil reservoir of the South Ordos basin,combined with core,logging and drilling data,casting thin sections,microscopic imaging and experimental test data to make a study on the reservoir characteristics including basic geological characteristics,sand body structure,micro-pore structure,seepage characteristics and rock mechanics.then choose and fit these characteristic parameters which can reflect the reservoir characteristics in maximum,establish a standard for the classification and evaluation of tight oil reservoirs which can be used as a guide for choosing favorable reservoirs during tight oil development process in study area.And then make a classification for the tight oil reservoir in the study area.On the basis of the Chang7 tight oil reservoir characteristics,after comprehensive consideration,the four aspects including reservoir sand body structure,pore structure,seepage characteristics and reservoir rock mechanics were determined to be used for evaluationing reservoir in study area.Two qualitative evaluation parameters including reservoir sand structure,water oil displacement type and six quantitative evaluation parameters including flow zone indicator,the largest roared radius,movable fluid effective porosity,the range of oil-water two phase seepage zone,start-up pressure gradient and reservoir rock mineral brittleness index were selected in the evaluation process which can be used for establishing the standard of reservoir classification and evaluation.The physical property of box-type sand body is the best,and the bell-type secondly,with the minimum porosity and permeability,the property of funnel-type and finger-type sand body are poorer.The larger flow zone indicator numerical value indicates the better matching of the pores and the throats.The permeability of the tight reservoir is mainly controlled by its maximum throat radius.The movable fluid effective porosity can reflect the physical properties and pore throat configuration structure of reservoirs.The water oil displacement type can be a qualitative characterization of reservoir seepage capacity.The larger the range of oil-water two phase seepage zone,the better the reservoir seepage capacity.The start-up pressure gradient shows very good negative correlation with the gas permeability of reservoir core,and the larger the start-up pressure gradient reflect the worse seepage capacity of reservoir.Both mineral brittleness index and mechanical brittleness index are used to evaluate the rock mechanics characteristics of reservoir.Research shows that the reservoir mineral brittleness index and mechanical brittleness index changes consistently,but due to the influence of the internal fracture in the reservoir,the mechanical brittleness index is overall smaller than mineral brittleness index,so the preferred mineral brittleness index is selected to evaluate the reservoir rock mechanics characteristics in this study.Based on the selected eight evaluation parameters,fitting the six quantitative evaluation parameters with six units classification method to get the quantitative comprehensive evaluation index Feci,then combine feci with the other eight parameters to establish the tight oil reservoir classification standard.Then classify the tight oil reservoir of study area with the classification and evaluation standard built for ???class.