塔河油田缝洞型油藏注气提高采收率机理研究

Study on the mechanism of enhanced oil recovery by gas injection in fracture-vug reservoir of Tahe oilfield

自2012年塔河油田开展了单井注氮气矿场试验,并取得了较好的效果。但是注气提高采收率的机理不清。通过调研,世界范围内注气提高采收率通常采用二氧化碳气体。在高温高压条件下进行了物理实验,结合理论计算,对二氧化碳及氮气在塔河油田条件下的最小混相压力,在原油中的溶解度,对原油密度、粘度的影响,以及在原油中的体积膨胀系数等进行了深入研究。由此得出了注入二氧化碳及氮气提高塔河油田缝洞型油藏采收率的机理。在塔河油田重质油条件下,二氧化碳/氮气与原油均不会发生混相。二氧化碳在原油中的溶解度大,对原油密度的改变作用更大,对原油的降粘作用更明显。因此,二氧化碳可以改善原油流动性,扩大波及体积。但是,氮气在原油中的混相压力更高,更容易形成气顶,对油水的重力分异能力强。

The field test of nitrogen injection in a single well has been carried out in Tahe oil field since2012,and a good result has been achieved.However,the mechanism of enhanced oil recovery by gas injection is not clear.Through the investigation,enhanced oil recovery by gas injection in the world usually uses CO_2.Physical experiments were carried out under the conditions of high temperature and high pressure.Combined with the theoretical calculation,the minimum miscible pressure of CO_2 and N_2 in Tahe oil field,the solubility of CO_2 and N_2 in crude oil,the impact of oil density and viscosity,as well as in the crude oil volume expansion coefficient arestudied.The mechanism of enhancing oil recovery by injecting CO_2and N_2 was obtained.In the condition of heavy oil in Tahe oil field,the CO_2 and N_2 with the crude oil will not be miscible.The solubility of CO_2 in the crude oil is bigger than N_2,the change effect to the density of crude oilofCO_2 is bigger than N_2,and the viscosity reducing effect to the crude oil of CO_2 is more obviousthan N_2.Therefore,CO_2 can improve the fluidity of crude oil,expand the swept volume.Meanwhile,the miscible pressure of N_2 in crude oil is higher,and the gas cap is much easier to formed,the ability of gravity differentiation is stronger than CO_2.