Drilling fluid is called "blood" of drilling. In shale gas exploration in China, the wide use of potassium formate drilling fluid has made a breakthrough in deep well drilling with domestic oil-based drilling fluid technology. The PH value has no requirement for the range of potassium formate drilling fluid.

The Concept of PH Value of Potassium Formate Drilling Fluid

The PH value of the drilling fluid is the PH value of the drilling fluid, which indicates the acidity and alkalinity of the drilling fluid. It is equal to the negative logarithm of the hydrogen ion concentration in the drilling fluid, also known as PH. When the PH is less than 7, the drilling fluid It is acidic. When the PH is equal to 7, the drilling fluid is neutral. When the PH is greater than 7, the drilling fluid is alkaline. The PH of the drilling fluid is usually determined by colorimetry.

Effect of PH on potassium formate drilling fluid

PH value has a great influence on the performance of potassium formate drilling fluid. Clay particles in drilling fluid are more stable in alkaline medium because of the large negative charge and cation exchange capacity. Secondly, there are many organic treatment agents, which must be alkaline to play a role, such as tannin, humic acid, etc. In addition, the PH value is low, organic treatment agents are easy to ferment and deteriorate at high temperature, so the PH value of potassium formate drilling fluid is generally maintained at more than 8.

However, if the PH value of high hydroxide ion adsorbed on the clay surface will promote the hydration and expansion of bentonite, which is not conducive to collapse prevention. Experience shows that all kinds of drilling fluids have their own suitable range of PH value. For example, high alkaline drilling fluid PH is 12-14, non-dispersive low solid drilling fluid PH is 8-9, weak acidic drilling fluid and saturated brine drilling fluid PH is 6-7, PH value is controlled in a suitable range, potassium formate drilling fluid has low viscous shear, small water loss and relatively stable performance. In addition, PH value is the basis for determining the treatment agent-alkali ratio.

Experiments show that KCl/BaSO₄/CaCO₃ drilling fluid and potassium formate/CaCO₃ drilling fluid (density is about 1.52kg/L) are generally used to stabilize shale and balance formation pressure when drilling in Unayzah-B reservoir in Saudi Arabia.