The Study On Carbon Dioxide-Nitrogen Flooding In Low Permeability Layer

This paper is part of National Science and Technology Major Project in 13th Five-Year,?2017ZX05009004?"low permeability and dense reservoir high efficiency improvement of recovery technology"the task"low permeability and ultra-low permeability reservoir compound gas improvement CO₂ gas drive feasibility study".In low or ultra-low permeability reservoir,carbon dioxide flooding have a better flooding efficiency but the resource shortage;The nitrogen flooding efficiency poor and miscibility pressure high but the resource abundant.So the nitrogen flooding application effect is poor.In order to solve this problem,This article used the YS oil field as the study background.Live crude has been preparation,through saturated the out-put gas.The oil physical data under the high pressure in this field also has been measured and the fluid parameter has been matched by CMG.According to the formation and fluid physical parameters,under the slim pipe model,the distribution of carbon dioxide and nitrogen in oil phase and gas phase,the mole fraction changing of C₂^C₄and C⁺₂₂ in oil phase during the carbon dioxide–nitrogen flooding process have been analyzed;the carbon dioxide plug size and the flooding method.The numerical simulation has been processed in order to study how to effect the oil recovery under the different length-thickness ratio,permeability,carbon dioxide slug size in homogeneous model.The result shows that when the length-thickness ratio is under the 100,as the value increased the oil recovery goes high.When the value is over the 100 then the oil recovery becomes steady.So the oil layer's thickness which less the 1%well spacing will have a good effection on oil recovery;When the length-thickness ratio is 30,the best carbon dioxide slug size is 0.3PV;As the permeability increased,the oil recovery decreased.More carbon dioxide will be used to reach the point.That means,lower permeability will benefit the carbon dioxide–nitrogen compound flooding.Based on the numerical simulation,natural core which confirm the experiment condition has been chosen then the physical experiment of oil flooding has been finished.The result shows that when the size of carbon dioxide slug is 0.3PV,the oil recovery closed the carbon dioxide flooding's value;Which improved that 0.3PV carbon dioxide slug can blocked off the nitrogen breakthrough.Comparing different permeability core's result,the oil recovery becomes high when the permeability decreased.The experiment model has been simulated.The simulated result is close to the experiment result which improved the result is reliable,It lays a solid foundation for the follow-up research?Affected by reservoir rhythmicity,permeability contrast and,using carbon dioxide-nitrogen compound flooding in ultra-low permeability non-homogeneous reservoir will influence the oil recovery.These questions have been calculated through the numerical simulations.The result shows that the higher heterogeneity,the lower oil recovery in reservoir,the less carbon dioxide injection should be needed to achieve the maximum recovery;because of the gravitational differentiation and fluid exchange between the oil layers,using carbon dioxide-nitrogen compound flooding in non-interbedded positive rhythm reservoir will have a better recovery than positive rhythm of interbedded reservoir,negative rhythm of interbedded reservoir and negative rhythm reservoir without interbed;when the permeability contrast is a constant,the larger length-thickness ratio,the later the gas breakthrough and the higher oil recovery.