聚合物在高渗岩心的堵塞及反应型防吸附体系的作用机理

Blockage of Polymers in High Permeability Cores and Mechanism of Reactive Anti-adsorption System

针对河南油田注聚井堵塞严重、注入井压力升高、产量下降的问题,采用油田提供的岩心及相应区块的聚合物样品进行物理模拟和分析测定实验。岩心流动、扫描电镜(SEM)和核磁共振测定皆表明聚合物在岩心中存在滞留现象,严重影响了后续水驱采收率。通过SEM扫描发现0-1/8处岩心孔道表面附着有较多聚合物,但孔喉半径仍然很大,且远大于聚合物尺寸,说明注聚合物时发生的堵塞主要是由吸附引起的;1/8-1/4处岩石裸露的颗粒表面积较大,注聚后这些颗粒表面及孔隙内表面吸附了大量聚合物分子,形成附着层,是岩心注聚堵塞的主要原因;而1/4-1/2处和1/2-3/4处以及尾端相比1/8-1/4和0-1/8处岩心表面吸附的聚合物比较少,岩心的堵塞情况比较轻微,由此说明注聚时堵塞主要发生在近井地带。针对堵塞原因,研发出的防吸附剂最终将强水湿性砂岩表面改变成弱疏水状态(106°),砂岩表面的润湿性得到了反转。防吸附剂与水水解成硅羟基化合物,在一定条件下与地层反应,将地层表面改性成疏水表面,进而降低聚合物吸附量。通过红外分析,结果表明1085.38cm^(-1)处强而宽的吸收峰归属于Si-O-Si键的反对称伸缩振动峰,说明防吸附剂和石英表面裸露的硅羟基发生反应生成Si-O-Si键,使得防吸附剂疏水基团裸露在外面,从而使得岩石表面变成疏水表面。

For the problems of severe plugging of polymer injection wells, injection well pressure increasing and production decline in Henan oilfield, physical simulation and analysis experiments of cores and corresponding polymer samples provided by the oilfield were carried out. Scanning electron microscopy(SEM) and nuclear magnetic resonance measurements all showed that polymer remained in the core, which seriously affected the subsequent water flooding recovery. Through SEM scanning, it was found that there were more polymers attached to the surface of the core channel at 0-1/8 core, but the pore throat radius was still large and much larger than the polymer size, indicating that the blockage caused by polymer injection was mainly caused by polymer adsorption. The surface area of the exposed particles at 1/8-1/4 core was relatively large. After the polymer injection, a large number of polymer molecules were adsorbed on the surface of the particles and the inner surface of the pores to form an adhesion layer, which was the main reason for the plugging of the core. Compared with 1/8-1/4 and 0-1/8 core, there was less polymer adsorbed on the surface of the core at 1/4-1/2, 1/2-3/4 core and the tail end of core, and the core was blocked more slightly, which showed that the blockage mainly occurred in the near-well zone during the polymer injection. For the plugging of polymer injection wells, the anti-adsorbent finally changed the strongly water-wet sandstone surface to weak hydrophobic surface(106°), and the wettability of the sandstone surface was reversed. The anti-adsorbent was hydrolyzed into silicon hydroxyl compound with water, and then reacted with the solid surface under certain conditions to modify the rock surface to hydrophobic surface, thereby reducing the amount of polymer adsorption. It was shown that the strong and broad absorption peak at 1 085.38 cm^(-1) was attributed to the anti-symmetric stretching vibration peak of the Si-O-Si bond through IR measurement, indicating that the anti-adsorbent reacted with the exposed silicon hydroxyl group on the quartz surface to form the Si-O-Si bond, exposing the hydrophobic group of the anti-adsorbent to the outside to make the rock surface hydrophobic.