Construction of tough hydrogels based on heterostructure double crosslinking strategy for flow control in harsh reservoirs.

Polymer hydrogels, as an effective technology that significantly reduces plugging in highly permeable formations, have been demonstrated to have important applications in deep profile control and enhanced recovery in complex reservoirs. While conventional preformed particulate gels (PPGs) have limited mechanical strength and thermal stability after swelling, restricting their practical application in oilfields. To construct a heterostructure double crosslinking structure hydrogel, methacrylated lignosulfonate (MLS) was synthesized as crosslinking agent and reacted with N, N'-methylenebisacrylamide (MBA) and functional monomers, including acrylamide (AM), acrylic acid (AA), N-methylolacrylamide (NMA), and 2-acrylamido-2-methylpropane sulfonic acid (AMPS). MLS acts as a macromolecular crosslinker that can interact with monomers such as AM, AA, AMPS, and NMA, forming heterogeneous crosslinked network through covalent (chemical bonds) and physical interactions (hydrogen bonds and π-π stacking). Its long-chain topology can also form a loosely connected primary network with the monomers, which is able to form a mechanical complementary effect with the short-chain localized network of MBA, thus realizing the optimization of the hydrogel mechanical properties and swelling properties. The hydrogels demonstrated remarkable mechanical properties, including a superior modulus of elasticity (G' = 42,368 Pa), high strength (0.14 MPa), and excellent toughness (2.96 MJ⋅m). Additionally, their swelling behavior was evaluated under varying temperature and salinity conditions, revealing that hydrogels maintained stable performance even under harsh environmental. Water-driven tests conducted in natural fractured rock cores showed that the hydrogel achieved a breakthrough pressure of 194 psi/ft at a flow rate of 0.5 mL/min, effectively meeting the water-plugging requirements for high temperature and salt reservoirs.