纳米-滑溜水在致密砂岩中的滞留及其对微观孔隙结构的影响

纳米材料已被证明可以提高非常规油气采收率,但其在储层孔隙中的吸附与滞留机理尚未明确。本文以大庆油田上白垩统青山口组致密砂岩为研究对象,采用低温液氮吸附、润湿角测定、扫描电镜、核磁共振及离心实验方法,研究了纳米-滑溜水压裂液在孔隙中的吸附与滞留,以及其对微观孔隙结构参数的影响。结果表明,纳米滑溜水压裂液处理后,扫描电镜观察到纳米颗粒在孔隙中滞留,岩石润湿角降低30.28%~58.17%；孔隙结构由平板孔向墨水瓶孔过渡,比表面积及吸附量显著增加；微孔占比减小20%~25%,过渡孔占比增大21%~26%,总孔体积增大；分形维数变小更接近2,孔隙结构变简单。纳米颗粒在储层孔隙中的吸附与滞留,导致微观孔隙结构发生变化。实验结果与认识对纳米-滑溜水压裂液在致密砂岩储层中的应用具有重要意义。

Retention of nano-slickwater in tight sandstone and its effects on microscopic pore structure

Nano-materials have proven to be successful in improving hydrocarbon recovery in the unconventional oil and gas reservoir, but the mechanism of their adsorption and retention in the pores is not yet clear. Taking the tight sandstone of Qingshankou Formation of Upper Cretaceous in Daqing Oilfield as the research object, the adsorption and retention of nano-slickwater fracturing fluid in pores and its effects on microscopic pore structure were studied by means of low-temperature nitrogen adsorption, wetting angle measurement, scanning electron microscopy, nuclear magnetic resonance and centrifugal experiment. The results show that the nano-particles are retained in the pores and the wetting angle of the rock decreases by 30.28 % ~ 58.17 % after the nano-slickwater fracturing fluid treatment. The pore structure transits from flat hole to ink bottle hole, and the specific surface area and adsorption amount increase significantly. The pore structure transitions from the plate-like to the ink-bottle-like, and the specific surface area and adsorption amount increase significantly. The proportion of micropores decreases by 20%~25%, the proportion of transitional-pores increases by 21%~26%, and the total pore volume increases. The fractal dimension becomes smaller and closer to 2, and the pore structure becomes simpler. The adsorption and retention of nanoparticles in the pores of the reservoir lead to changes in the microscopic pore structure. The experimental results and understanding are of great significance for the application of nano-slickwater fracturing fluid in tight sandstone reservoirs.