Experimental study of low molecular weight polymer/nanoparticle dispersed gel for water plugging in fractures

A low molecular weight polymer/nanoparticle dispersed (LPND) gel system applied for water plugging in fractured media was studied. Results of rheological and gelation properties measurements show that the LPND gelant has a satisfactory shear resistance performance and its shear viscosity can continuously level off under high shear rate condition. The internal structure of the LPND gelant which shows a state of "buttery" can rapidly recover from the state of nanoparticle random distribution to the foliated structure and finally to the reticular structure, and the increase of temperature contributes to the structural recovery ability. Moreover, the increase of the accelerating agent concentration can significantly enhance the gel strength of the LPND gel which shows a "rubbery" state and evidently shorten both the critical and final gelation times. The propagation, plugging and enhanced oil recovery (EOR) performances of the LPND gel system in fractured media were also investigated. Results show that the LPND gelant has slight gravity settling phenomenon which contributes to the uniform gelant propagation in fracture; it can effectively fill the whole water-flooded fracture space and improve the water plugging performance after the gel formation. In the multi-stage fractures, the LPND gelant manifests a selective filling characteristic; it preferentially fills the fracture with high water content and then diverts the subsequent injected water to the adjacent fracture and matrix with low water content after gel formation, resulting in the significant enhancement of the sweep efficiency and oil recovery.