With the development of drilling technology, the exploration and development of some oil and gas resources is very difficult. Many oil and gas reservoirs not only have large water depth and low mud line temperature, but also have the characteristics of high temperature and high pressure in the lower section. Why is potassium formate more suitable for use in drilling fluids? Because potassium formate is mainly used to prepare injection fluid for water-bearing oil wells and drilling fluid system with potassium formate, it has outstanding advantages such as strong inhibition, good compatibility, environmental protection and reservoir protection.

On the one hand, the low temperature environment of sea water causes the increase of drilling fluid viscosity, shear force and rheological property in riser section, which leads to the increase of cyclic equivalent density and leads to lost circulation.

On the other hand, the reservoir environment of high temperature and high pressure in deep water causes the drilling fluid window to be narrower than that of conventional deep water wells. Drilling fluid should not only resist high temperature but also prevent overflow, but also restrain the collapse of loose formation, and increase formation pressure to expand the safety window.

So the main difficulties of drilling fluid include:

(1) Because of the high formation pressure at the bottom of the well and the high density of drilling fluid, the rheology of high density drilling fluid is difficult to control at high temperature.

(2) Drilling fluid should have good inhibition, maintain mudstone wellbore stability and ensure safe drilling;

(3) Drilling fluids should have good anti-pollution ability, wide solid-phase capacity limit and good anti-drilling cuttings pollution ability under high temperature and high density conditions.

(4) Drilling fluids should have low HTHP filtrate loss and good mud cake quality, reduce filtrate invasion and do well reservoir protection.

Potassium formate is a new additive for drilling and completion fluids, which has the advantages of strong inhibition, high temperature stability, good compatibility, low corrosivity, good environmental protection and reservoir protection. The effects of potassium formate concentration, dissolution temperature and time on the solubility of sodium chloride and calcium sulfate were studied in laboratory.

The results show that temperature has a great influence on the solubility of calcium sulfate in potassium formate solution. The solubility of calcium sulfate in potassium formate solution at the same concentration increases with the increase of temperature, and the solubility of sodium chloride is also greatly affected by temperature. Potassium formate can significantly improve the low temperature resistance of polymers, so NaCl and potassium formate will be used as a combination of low temperature hydrate inhibitors.