1. . 
Two emulsion types are used as muds:
See: amides, amines, calcium chloride, coalescence, colloid, creaming, demulsifier, electrical stability test, emulsion mud, external phase, formation damage, HLB number, hydrophile-lipophile balance number, internal phase, invert-emulsion oil mud, invert-emulsion oil mud, oil-mud emulsifier, oil/water ratio, surface tension, water-based mud, water-in-oil emulsion, water-mud emulsifier
2. . 
A type of damage in which there is a combination of two or more immiscible fluids, including gas, that will not separate into individual components. Emulsions can form when fluid filtrates or injected fluids and reservoir fluids (for example oil or brine) mix, or when the pH of the producing fluid changes, such as after an acidizing treatment. Acidizing might change the pH from 6 or 7 to less than 4. Emulsions are normally found in gravel packs and perforations, or inside the formation. Most emulsions break easily when the source of the mixing energy is removed.
However, some natural and artificial stabilizing agents, such as surfactants and small particle solids, keep fluids emulsified. Natural surfactants, created by bacteria or during the oil generation process, can be found in many waters and crude oils, while artificial surfactants are part of many drilling, completion, or stimulation fluids. Among the most common solids that stabilize emulsions are iron sulfide, paraffin, sand, silt, clay, asphalt, scale, and corrosion products. Emulsions are typically treated using mutual solvents.
3. . 
A dispersion of droplets of one liquid in another liquid with which it is incompletely miscible. Emulsions can form in heavy oils that contain a significant amount of asphaltenes. The asphaltenes act as surfactants with treatment or formation water. The resulting emulsion droplets have high-energy bonds creating a very tight dispersion of droplets that is not easily separated. These surface-acting forces can create oil-in-water emulsions, water-in-oil emulsions, or both. Such emulsions require temperature and chemical treating in surface equipment to separate.