| After nearly 20 years of polymer flooding development in Lamadian Oilfield,the comprehensive water cut of polymer flooding in the first oil layer has reached more than 98%,and the polymer injection object has been shifted to the second oil layer.The second type oil reservoir includes the second type A oil reservoir and the second type B oil reservoir.The geological characteristics and development status of the second type oil reservoir are different from that of the first type reservoir.Therefore,it is necessary to carry out in-depth research on the microscopic pore structure and remaining oil distribution of the second type oil reservoir.The most important thing is to accurately predict the distribution of remaining oil after water and polymer flooding.By understanding the current development effect of water and polymer flooding in the second oil layer of Lamadian Oilfield,the microscopic remaining oil type and pore structure of the stratum at the present stage can be determined,and the development effect of polymer flooding in other second oil layers can be predicted.Therefore,it is necessary to study the microscopic pore structure and remaining oil of the second oil layer in Lamadian Oilfield.Through scanning electron microscopy(SEM)and constant speed mercury intrusion method to study the oil level of different permeability core internal microscopic pore structure characteristics,set up the second type reservoir microscopic pore structure types of classification method,made the boundaries of various types of reservoir,will the second class A and B reservoir microscopic pore structure types each subdivided into three categories,The permeability range is 800-2500×10-3?m2,porosity is 31%-32%,main pore size is 375-350?m,average pore radius is 300-330?m,main throat size is 18-22?m,average throat radius is18-20?m,main pore type is dissolution pore is defined as AI class;Permeability range of600-800×10-3?m2,porosity of 28%-29%,main pore size of 210-300?m,average pore radius of240-260?m,main throat size of 11-17?m,average throat radius of 11-13?m,main pore type of intergranular pores defined as AII;Permeability range of 400-600×10-3?m2,porosity of31%-32%,main pore size of 200-275?m,average pore radius of 240-260?m,main throat size of8-12?m,average throat radius of 9-11?m,main pore type of dissolution pores defined as AIII;Permeability range is 600-1300×10-3?m2,porosity is 31%-32%,main pore size is 150-250?m,average pore radius is 180-220?m,main throat size is 5-9?m,average throat radius is 5-7?m,main pore type is intergranular pore,which is defined as BI;Permeability range is400-600×10-3?m2,porosity is 25%-30%,main pore size is 150-200?m,average pore radius is200-220?m,main throat size is 5-9?m,average throat radius is 5-7?m,main pore type is dissolution pore and intergranular pore are defined as BII;Permeability range is200-400×10-3?m2,porosity is 18%-27%,main pore size is 120-180?m,average pore radius is150-170?m,main throat size is 0.4-2.4?m,average throat radius is 1-3?m,main pore type is intergranular pore is defined as BIII.In addition,the distribution of remaining oil after water flooding and polymer flooding was studied by casting thin slices combined with fluorescence analysis experiment.The results show that the remaining oil of various types decreases most in cluster form,followed by film form,then corner form,and finally throat form.After water flooding,the remaining oil in membrane form,throat form and corner form is mainly distributed between 47%and 51%,and the remaining oil in cluster form is mainly distributed between 30%and 38%.After polymer flooding,the remaining oil in membrane form is mainly distributed between 55%-60%,the remaining oil in throat form and corner form is mainly distributed between 5%-10%,and the remaining oil in cluster form is mainly distributed between 20%-25%.After water flooding,the remaining oil of type B reservoir is mainly distributed between 35%-41%in membrane form,5%-10%in throat form and corner form,and 42%-48%in cluster form.After polymer flooding in type B reservoir,the remaining oil in membrane form is mainly distributed between 38%and43%,the remaining oil in throat form and corner form is mainly distributed between 5%and10%,and the remaining oil in cluster form is mainly distributed between 40%and 45%.By comparing the microscopic remaining oil changes before and after polymer flooding,it is found that polymer flooding has achieved a good effect and greatly improved the exploitation degree.However,some remaining oil cannot be recovered in the late flooding period,so further research and development plans are needed. |
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