In deepwater environments, where the water depth is greater than 800 m, hydrate formation in the drilling wellbore becomes a crucial problem for flow assurance and wellbore pressure management. In this work, the influences of xanthan gum (XG), carboxymethyl cellulose (CMC), and hydrate concentration on methane hydrate formation are investigated experimentally under bubbly flow using a horizontal flow loop at pump frequencies from 18 to 24 Hz, CMC concentrations from 0.2(wt)% to 0.5(wt)%, XG concentrations from 0.1(wt)% to 0.3(wt)%, and hydrate concentrations from 0% to 8.35%. The experiments show that increases in XG concentration, CMC concentration, and hydrate concentration all lower the hydrate formation rate in the flow loop. XG and CMC play similar roles as kinetic hydrate inhibitors for hydrate prevention, where CMC has a better hydrate inhibition function than XG. From the viewpoint of the mass transfer mechanism, an increase in these three factors can increase the apparent viscosity and the surface tension of the continuous phase and can reduce the gas-liquid interfacial area, which finally lowers the mass transfer rate between gas and liquid, as well as the hydrate formation rate. Moreover, the increase in the hydrate concentration causes obvious reductions in the flow velocities and increases in the pressure drops of the hydrate slurry, which indicates hydrate plugging in the flow loop.