Delayed-Crosslink Hydrogel for Improving Oil Recovery in Differential Heterogeneous Reservoirs

Premature water production is an inevitable issue that results in loss of quantities of reserves in heterogeneous oilfields especially with large permeability ratios. Hydrogel treatments, preferentially plugging large channels, are efficient techniques to reduce excessive water circulation. In this work, a moderate delayed polyacrylamide hydrogel was fabricated applying in-depth plugging to promote oil production. Suitability tests of delayed hydrogel in the presence of quartz sand confirmed its mature delay over 10 days, providing the low-viscosity gelant sufficient time for entering the deep layer. Single sand-pack displacement tests demonstrated the excellent plugging ability in differential permeability layers to strongly promote the follow-up oil production. Aiming at heterogeneous reservoirs with three different permeability ratios, conventional displacements and hydrogel treatments were sequentially conducted. In comparison with water- and polymer-flooding that mainly performed exploitation at low-permeability-contrast layers (K _high/K _low = 3), the delayed hydrogel technique after polymer-flooding was capable of improving the oil recovery efficiency of unswept zones at high-permeability-contrast zones (K _high/K _low ≥ 10). Recovery in heterogeneous layers with permeability ratios (K _high/K _low) of 10 and 15 was enhanced to 48 and 59%, respectively from 18 and 0%. In addition, rheological behaviors and morphologies elucidated the delayed hydrogel with extruding deformation and high yield strength, facilitating water shutoff and improvement of oil production.