Abstract:

To address the limitation of conventional physical plugging materials for poorly cemented fractured formations and solve borehole wall collapse and rockfall problems encountered in drilling complex loosefractured strata, sodium alginate (SA)/polyacrylamide (PAM) interpenetrating network gel material was prepared，with acrylamide (AM) as monomer, ammonium persulfate (APS) as initiator, N,N′-methylenebisacrylamide (MBA) as crosslinker, and D-glucono-δ-lactone (GDL) as a sustained-release calcium source. The rheological properties and microstructure of the gel were characterized using a rheometer and scanning electron microscope. The effects of SA mass fraction, mass ratio of CaCO3 to SA, and crosslinking agents on the rheological behavior of the gel were investigated. The gel formula with optimal mechanical properties was obtained through optimization, with the component concentrations as follows: 0.01 g/mL SA, 0.15 g/mL AM, 0.000 5 g/mL APS, 0.000 6 g/mL MBA, 0.004 g/mL CaCO3 and 0.004 g/mL GDL. The results show that the optimal composite gel achieves a maximum elongation at break of 810% and a maximum tensile stress of 0.11 MPa. Its viscosity and shear force increase over time, indicating the progressive formation of a multinetwork crosslinked structure within the system. Complete gelation is achieved at 60 ℃ in approximately 1.5 h. The composite gel material can effectively fill and cement fractured rock layers with different porosities， and after complete gelation, zero fluid loss is achieved under 0.69 MPa pressure. Additionally，the cemented rock sample remains structurally intact even at a compressive deformation of 50%.

Key words: sodium alginate, polyacrylamide, full interpenetrating polymer network, wellbore stability