Study on the penetration of strengthening material for deep-water weakly consolidated shallow formation

Abstract

Unformed-rock silt and sand are the main components of shallow formations in deep-water oil and gas wells. The formations are different from the perspective of mechanical performance of the cement sheath and often causes brittle failure. Improving the cement system or cement-formation interface strength is not sufficient to solve this problem. This study tested solid and liquid strengthening materials to increase the mechanical performance of weakly consolidated shallow formations and to minimize the performance difference with cement stone. The test of the groutability of superfine slag, cement, and epoxy resin indicated that waterborne epoxy resin system is the best choice. An annular simulation core was used to evaluate the penetration of the epoxy resin system. The simulation cementing experiment indicated that the viscosity of the ER (epoxy resin) slurry and the compression degree of the core negatively correlated with the permeate depth, while the grouting pressure exhibited positive correlation. The permeate depth can reach 11.8 mm under 0.1 MPa while the maximum was 21.7 mm at 0.4 MPa. A thin ER layer was formed between the cement sheath and the core after the ER slurry was cured, which increased the cement-formation interface strength by 22.18 %. Standard blocks showed that 5% of ER can increase the strength of unconsolidated clay to 2.17 MPa. SEM indicates that the ER filled part of the space between the particles of clay and consolidated them. The difference between standard blocks and core samples after treatment in SEM was low. The difference in mechanical performance between the cement stone and the weakly consolidated formation was narrowed after the formation was reinforced. • The groutability of solid and liquid strengthening material was evaluated. • The effect of grouting pressure, compress degree, and slurry viscosity on the permeate depth was studied. • The mechanism of epoxy resin to reinforce the weakly consolidated shallow formation and improved the cement-formation interface strength was revealed. • The mechanical properties between the cement sheath and the weakly consolidated formation were narrowed.