Definition - What does Dispersed Mud mean?
Dispersed mud (or dispersed drilling fluid) is a water-based mud that is treated with chemical dispersants to deflocculate clay particles or mud solids, and allow better rheology control in muds with high density.
The dispersant present in dispersed muds increases its tolerance to solids, allowing weights up to 20 ppg. However; a dispersed mud system laden with solids can significantly decrease the rate of penetration and erode the hole. To maintain the pH level of the dispersed mud between 10 to 11, caustic soda (NaOH) is added.
Trenchlesspedia explains Dispersed Mud
The chemical dispersants used in dispersed muds such as lignite and lignosulfonate are acidic in nature and require an alkaline environment. High pH muds are more tolerant of solids and contamination than muds that are acidic or with low pH. NaOH is used for achieving the required pH and weighting materials are added for adjusting the density. Bentonite clay is an agent used as a viscosifier; dispersants act by permitting enough clay into the system to control fluid loss. There are two types of dispersed muds - calcium-based mud and seawater mud.
Calcium-based mud systems maintain the required amount of calcium in the water phase by using gypsum or lime. These muds are more inhibitive and tolerant than freshwater dispersed fluid toward cement and anhydrite contamination. Seawater mud systems are suitable for offshore environments where it is cheaper than transporting freshwater for the operation.