Abstract
In view of the problems in which the solid content of drilling fluid increases in the middle and late stages of horizontal well drilling, the lubricity of mud cakes on the borehole wall decreases, and the friction of pipe string increases due to the gradual thickening of mud cakes, which leads to the sticking and the obvious decrease of cementing strength at the second interface, a mud cake improver Mul-GX with lubrication and interface enhancement effect was studied in this paper. Based on the hydration and filling mechanism, the lubricity of the mud cake was improved, its thickness was reduced, and its strength was improved through synergistic effects of solvated water film lubrication and buffering, hardening and crystallization of gelled substances, and filling and dispersion of elastic particles. The mud cake improver Mul-GX is composed of the metasilicate GX-ZQ, polymer copolymer GX-JB, and polymer GX-TX, and the mass ratio of each component was GX-ZQ: GX-JB: GX-TX = 15:1:0.5. The effect of Mul-GX was evaluated through the performance determination of the mud cake and interface cementing simulation experiments. In addition, the microscopic characterization by SEM and XRD were carried out to analyze the mechanism of Mul-GX. The experimental results showed that when Mul-GX was added to the water-based drilling fluid with the 1.0%-1.5% adding quantity, the mud cake lubricity improved by more than 60%, its thickness reduced by 53.9% on average, and its strength increased by 54.3% on average. At the same adding quantity, the interfacial bonding strength was 4.4 times more than the data before adding Mul-GX. All of the results showed that Mul-GX has obvious mud cake lubrication effect and interface enhancement effect.