Marine gas hydrates have now become a hotspot of energy resource researches. Drilling is indispensable when exploring and exploiting gas hydrates existing in deep water. But it will be confronted with more complicated safe problems than that of the conventional marine oil & gas drilling. Drilling fluid is the crux of gas hydrates drilling and its performance is extremely important to the well-off drilling.
The hydrates inhibition and low-temperature stability of formate based drilling fluids as well as effect of hydrates inhibitors on the fluids were evaluated elementarily by the experimental system of gas-hydrate integrative simulation (ESGHIS). The results show that a basic system of formate based drilling fluids, which composed of seawater,3% HCOONa, 3%SK-2, 0.2%KPAM,0.1%LV-PAC, 2%SMP-2 and 0.3% modified starch, has a good performance stability under low temperature environment(−5°C −15°C °C). Adding NaCl and KCl, thermodynamic inhibitors, has little effect on the rheology properties of the basic system, while PVP(K30), a dynamic inhibitor, has a great effect on those. The basic system has a low ability of hydrates inhibition when they are used in deep water over 1400m. Low dosage of PVP(K30) can improve increasingly the hydrate inhibition of the basic system, and the suitable concentration is about 0.5%. Therefore, the formate based drilling fluids which contain high concentration of salts and low dosage of hydrate inhibitors, can meet the needs of gas hydrates drilling in the deep water.