Definition - What does Alkaline mean?
Alkalinity is the opposite of acidity. When a sample of the water used to mix drilling fluid contains enough alkali materials, such as potassium carbonates, sodium carbonates or similar soil constituents, to raise the pH measurement of the sample to more than 7.0, the water is alkaline.
When the sample's pH is less than 7.0, the water is acidic.
Trenchlesspedia explains Alkaline
The alkalinity of drilling mud is important because drilling mud water should be neutral, neither acidic nor alkaline. This is because some mud components can be neutralized in an alkaline environment. Ensuring the drilling mud accomplishes all four of its goals requires testing regularly, using either an electronic testing meter or a litmus paper testing kit.