原油沥青质吸附与沉积对储层岩石润湿性和渗透率的影响

原油沥青质吸附引起的油藏岩石润湿性改变和沥青质沉积对储层孔喉的堵塞是造成储层损害、导致油井产能下降的重要机理之一。首先 ,采用改进的自吸速率法和分光光度法 ,研究了原油沥青质吸附所引起的砂岩岩样润湿指数的变化 ;然后 ,利用岩心流动实验方法 ,定量评价了稠油沥青质沉积对储层岩石渗透率的影响。实验结果表明 ,岩心润湿指数随沥青质吸附量的增加而减小 ,从而导致油相的相对渗透率降低。地层水的离子组成是影响水湿性的主要因素之一。地层水所含无机阳离子的化合价价数越高 ,它与沥青质的协同作用所引起的润湿指数下降的程度越大。储层岩心油相渗透率下降的程度与沥青质沉积量和储层岩心的原始渗透率有关 ,沉积量越大或原始渗透率越低 ,则油相渗透率下降幅度越大。因此 ,对于原油中富含沥青质的油藏 ,特别是稠油油藏 ,尽可能抑制沥青质的吸附和沉积是保护储层的一项重要措施。

Effect of adsorption and deposition of asphaltines in crude oil on wettability and permeability of reservoir rocks

The wettability alteration on rock surfaces induced by asphaltine adsorption and the plugging of pore throats caused by asphaltine deposition are the important mechanisms of formation damage. The change in wettability index induced by adsorption of asphaltine in crude oil was studied using the modified method of spontaneous imbibitions and spectrophotometry. In addition, the impact of asphaltine deposition on the permeability of reservoir rocks was evaluated using the procedures of core flooding test. The experimental results show that the values of wettability index decrease with the increase in adsorption of asphaltine in crude, which causes the decrease of relative permeability to oil. The ionic composition of formation brine is one of the main factors influencing the decrease in water wetness. The higher the valance of inorganic cation is, the more pronounced the decrease in wettability indices induced by their synergetic effect with asphaltine will be. The extent of decrease in permeability is related to the amount of asphaltine deposition and the initial formation permeability. The more the amount of deposited asphaltine and the lower the initial permeability of core samples are, the more drastic the decrease in permeability will be. Therefore, it is an important aspect in formation damage control to minimize the adsorption and deposition of asphaltine in crude for the oil reservoir with rich asphaltine, especially for the heavy oil reservoir.