原油沥青质沉积和吸附引起储层损害的机理及损害程度评价

原油沥青质沉积对储层孔喉的堵塞和沥青质吸附引起的油藏岩石润湿性改变是造成储层损害、导致油井产能下降的重要机理之一。首先,从热力学平衡和溶解度两个方面论述了原油沥青质发生絮凝和沉积的机理,并采用粘度法测定了沥青质絮凝初始点;然后利用岩心流动实验方法,定量评价了沥青质沉积对储层岩石渗透率的影响;并采用经改进的自吸速率法,研究了原油沥青质吸附所引起的润湿性改变及其对产能的影响。实验结果表明,储层岩心油相渗透率下降的程度与沥青质沉积量、储层岩心的原始渗透率、沉积颗粒粒径以及原油流速等因素有关。原油沥青质在油藏岩石上的吸附所引起的润湿性改变是导致储层油相渗透率降低,从而造成储层损害的一个重要原因。

Mechanism and Evaluation of Formation Damage Induced by Deposition and Adsorption of Crude Asphaltene

The plugging of pore throats caused by asphalting deposition and the wettability alteration on rock surface induced by asphalting adsorption is the important mechanisms of formation damage. Firstly, flocculation and precipitation mechanisms were described from the aspects of thermodynamic equilibrium and solubility, and the onset of flocculation was tested. Then, the effect of asphalting deposition on the permeability of reservoir rocks was evaluated through the method of core flooding test; In addition, the change in wettabilty induced by asphalting adsorption and its effect on productivity was studied using modified method of spontaneous imbibitions. From the experimental results , the decrease degree of core permeability was directly related to asphalting deposition amount, core original permeability, precipitated particle diameter and crude velocity. The wettability alteration on rock surface induced by asphalting adsorption was the main cause of permeability reduction.