超临界CO_2对普通稠油和超稠油物性的影响规律

Effect of Supercritical CO_2 on the Physical Properties of Conventional Heavy Oil and Extra-heavy Oil

超临界CO_2可溶于稠油中改善原油物性,进而提高其动用程度。为了研究注入CO_2对普通稠油和超稠油的作用机制的异同,本文通过物理模拟实验,深入探讨了超临界CO_2对稠油物性和沥青质沉积的影响,并采用微观手段分析了注超临界CO_2前后普通稠油和超稠油沥青质的结构。研究结果表明,注入超临界CO_2可有效降低普通稠油和超稠油的黏度,普通稠油的溶解气油比随着压力升高而增加,而超稠油中超临界CO_2很快达到饱和状态,溶解气油比仅有30 m3/m3左右。注入超临界CO_2会导致原油中沥青质絮凝沉积,在普通稠油中这种现象尤其明显,沥青质相对沉积量要比超稠油中沥青质的相对沉积量多大约30%。注入超临界CO_2后普通稠油沥青质的微观结构变化较大,由粗糙不平(胶质包覆在沥青质表面)变得平整光滑;而超稠油沥青质的微观结构变化不大,均为稳定的块状结构,这主要因为超稠油中沥青质含量较胶质高,沥青质间结构紧密,CO_2分子离散困难。

As a result of supercritical CO2 dissolution,the physical properties of heavy oil can be significantly improved,and thus leading to a mobilization efficiency. Herein,in order to gain the underlying interactions between heavy oil and supercritical CO2 deeply,the effect of supercritical CO2 on physical properties and asphaltene precipitation of two heavy oils was thoroughly examined,and the texture change of the asphaltene from conventional heavy oil and extra-heavy oil before and after CO2 injection was observed. The results showed that the viscosities of the heavy oils were noticeably reduced due to the dissolution of supercritical CO2. The dissolved gas-oil ratio of the conventional heavy oil increased with the increasing pressure,while for the extra-heavy oil,the gas-oil ratio was 30 m3/m3 at the saturation pressure. In addition,supercritical CO2 in the heavy oils caused the asphaltenes to agglomerate and subsequently to precipitate,especially for the conventional heavy oil,which produced approximately 30% more precipitatant than the extra-heavy oil did. Furthermore,the texture of the asphaltenes in the conventional heavy oil was notably altered to be smooth,as revealed by SEM observations. In contrast,a weak alteration of the asphaltene textures for the extra-heavy oil was observed due to the compacted architecture of asphaltenes and resin,which obstructed the entrance of CO2 molecules.