CO_(2)在老油田地质封存中的赋存状态

Study on the Existing State of CO_(2)in Geological Storage of old Oilfields

为研究CO_(2)在老油田地质封存中的赋存状态,采用室内实验的方法,研究了CO_(2)与地层流体、岩石的相互作用,并结合驱替实验结果明确了地质封存中CO_(2)的赋存状态。研究表明:油水共存情况下,CO_(2)主要溶解于原油中,在原油中的相对溶解量是水中相对溶解量的9.61倍;CO_(2)溶解所形成弱酸的量和浓度对固化作用起决定作用,在含气饱和度60%以下时,固化度随含气饱和度的增加而增加,在含气饱和度高于60%后,固化度急剧降低;驱替实验注CO_(2)量较小时,孔隙中CO_(2)主要为自由气、束缚气和油中溶解气,注CO_(2)倍数较大时,孔隙中自由气最多,束缚气次之;封存的长期性与驱替试验的短期效应有所不同,地质封存CO_(2)量较小时,CO_(2)在地层中主要为溶解气,形成以流体溶解为主的封存模式;地质封存CO_(2)量较大时,CO_(2)赋存状态中自由气最多,占69%,溶解气次之,占20%,束缚气最少,形成以自由气为主、溶解气为辅的地质封存模式。研究成果为深入研究CO_(2)的地质封存提供技术支撑,同时也为老油田CO_(2)驱开发提供重要参考。

In order to study the existing state of CO_(2)in the geological storage of old oilfields,the interaction of CO_(2)with formation fluid and rock was studied by means of laboratory experiments,and the existing state of CO_(2)in the geological storage was determined by combining the results of displacement experiments.Study shows that CO_(2)is mainly dissolved in crude oil,and the relative solubility in crude oil is 9.61 times of that in water under the condition that oil and water exist at the same time.The amount and concentration of weak acid formed by CO_(2)dissolution play a decisive role in the curing effect.When the gas saturation is below 60%,the degree of curing increases with the increase of gas saturation,and when the gas saturation is higher than 60%,the degree of curing decreases sharply.When the amount of CO_(2)injected in displacement experiment is small,CO_(2)in the pores is mainly free gas,bound gas,and dissolved gas in oil,and when the multiple of CO_(2)injection is large,free gas is the most in the pores,followed by bound gas.However,the long-term effect of storage is different from the short-term effect of displacement test,when the amount of geological storage CO_(2)is small,CO_(2)is mainly dissolved gas in the formation,forming a storage mode of fluid dissolution.But when the amount of geological storage CO_(2)is large,free gas is the most in CO_(2)existing state,accounting for 69%,and dissolved gas is the second,accounting for 20%,and bound gas is the least,forming the geological storage mode with free gas as the main and dissolved gas as the auxiliary.The research results provide technical support for the further study of CO_(2)geological storage,and also provide important reference for the development of old oilfields CO_(2)flooding.