Insights on the penetration and migration of chemically cross-linked systems in porous media

Abstract

Using the sand-packed tubes with different lengths (0.2–20 m) and different long flat-sand-inclusion visualization models, the penetration and migration laws, in-depth dynamic gelation and plugging characteristics, and the related mechanism of chemically cross-linked systems (HPAM/Cr3+) in porous media are investigated. The results show that there is an optimal concentration ratio between the polymer and the crosslinking agent, and the system of 4000 mg/L HPAM and 3000 mg/L SD-307 can obtain the gel with maximum strength (grade G) and breakthrough pressure gradient (3.13 MPa/m). The relatively weak system of 1800 mg/L HPAM +1000 mg/L SD307 (grade C) can present a similar injection pressure with the strong system of 4000 mg/L HPAM + 3000 mg/L SD307. Moreover, the onset and equilibrium of cross-linking agent production respectively lags behind polymer by at least 1.38 PV and 20.5 PV, and the adsorption amount of the crosslinking agent is 5111 μg/g greater than that of the polymer. Compared strong system (grade G) with the weak one (grade C), the former only has slight difference with the latter in the production and equilibrium of polymer but has significant difference in cross-linking agent. The corresponding injected volumes of production and equilibrium of polymer present significantly increase before the length of 1 m. Furthermore, the effluent of strong cross-linked system in 8 m in front of 20 m-long sand-packed tube exhibits the effective gelation and can achieve efficient plugging. On the contrary, the gel strength is very low or even the gelation is difficult as the migration distance exceeds 8 m. Although a greater fractional flow more than 75% can be achieved at high permeability under heterogeneous condition, the sweep of subsequent water to the low permeability layer after injecting the system become worse and worse with increasing injected volume (0.1–0.9 PV) due to the damage to the low permeability layer.