低渗致密砂岩储层孔隙结构特征及自发渗吸实验

为深入研究低渗致密砂岩储层渗吸驱油机理以及渗吸过程的影响因素,以鄂尔多斯盆地H区块长8储层段致密砂岩储层为研究对象,采用铸体薄片、扫描电镜以及恒速压汞等试验手段对孔隙类型、孔隙半径、喉道半径以及孔喉比等孔隙结构特征参数进行了分析,并利用渗吸实验和核磁共振实验对自发渗吸驱油特征及影响因素进行了研究。结果表明：研究区块致密砂岩储层孔隙类型以粒间孔、粒内溶孔和晶间孔等为主,主要分为中大孔型和微小孔型孔隙,这两类孔隙的孔隙半径相差不大,但孔隙数量、喉道半径以及孔喉比的差异较大。致密砂岩岩心自发渗吸初始阶段渗吸速度较快,后期逐渐下降,中大孔型的岩心自发渗吸驱油效果好于微小孔型岩心；随着致密砂岩岩心表面水润湿程度的增强,自发渗吸采收率逐渐增大；而随着渗吸液界面张力的降低,自发渗吸采收率呈现出先上升后下降的趋势,因此,在实际应用中,应使渗吸液具有合适的界面张力,从而使自发渗吸采收率达到最大。

Experimental Study on Pore Structure and Spontaneous Imbibition of Low Permeability Tight Sandstone Reservoirs

In order to study the mechanism of oil displacement by imbibition and the influencing factors of imbibition process in low permeability tight sandstone reservoir, the compact sandstone reservoir of Chang 8 reservoir section in H block of Ordos Basin was taken as the research object. The pore type, pore radius, throat radius and pore throat ratio were analyzed by means of casting slice, scanning electron microscopy and constant velocity mercury injection. The characteristics and influencing factors of spontaneous imbibition flooding were studied by imbibition experiment and nuclear magnetic resonance experiment. The results show that the pore types of tight sandstone reservoirs in the study area are mainly intergranular pore, intragranular dissolved pore and intercrystalline pore, which are mainly divided into medium-large pore and micro-pore. The pore radius of these two types of pore is not very different, but the number of pore, throat radius and pore-throat ratio are quite different. In the initial stage of spontaneous imbibition of tight sandstone cores, the imbibition rate is faster, and then gradually decreases. The effect of spontaneous imbibition and displacement of medium and large porous cores is better than that of micro-porous cores. With the increase of water wettability on the surface of tight sandstone cores, the spontaneous imbibition recovery rate increases gradually; and with the decrease of interfacial tension of imbibition, the spontaneous imbibition recovery rate increases first and then decrease. Therefore, in practical application, the appropriate interfacial tension should be applied to make the spontaneous imbibition recovery rate maximize.