Water-base Muds contain water as the liquid phase and are used to drill most of the wells in the world because they are relatively simple, expense is usually reasonable, and water is commonly available in most places.
Oil-base Mud contains either natural oil or synthetic oil as the continuous liquid phase and is used for maximum hole protection. Oilbase mud and synthetic oil mud are usually much more expensive than water-base mud and therefore are only used when there is a specific need, such as to keep the hole from swelling or caving in, or to reduce friction and prevent stuck pipe in very crooked or high angle holes. Either water-base or oil-base mud can be used as “weighted” mud.
Weighted Mud refers to any mud which has barite or barite substitutes added to increase density. These muds normally have a density greater than 10.0 lbs/gal. The solids in weighted mud consist of drilled solids from the hole, plus barite, plus commercial clays added to control fluid loss and viscosity.
Unweighted Mud refers to any mud which has not had barite added. This mud type normally has a density of less than 10.0 lbs/gal. The solids in unweighted mud consist of drilled solids from the hole, plus commercial clays.
Solids control techniques will vary considerably depending on the type of mud being used. For example, with many unweighted water-base muds, the loss of fluids along with the drilled solids may be economically insignificant, allowing simple solids control techniques. In the case of mud that contains expensive chemical additives and/or barite, especially oil-base mud, sophisticated solids control techniques must be utilized to minimize overall costs. In addition, environmental costs of haul-off and disposal may require sophisticated solids control techniques.
Here is a list of the most common mud types, followed by a brief description of each type:
Water-Base Mud (WBM)
A. Spud Mud
B. Natural mud
C. Chemically-Treated Mud
- Lightly Treated Chemical Mud
- Highly Treated Chemical Mud
- Low Solids Mud
- Polymer Mud
- Calcium Treated Mud
D. Saltwater Mud
- Sea Water Mud
- Saturated Salt Mud