various drilling fluids

Emulsion Drilling Fluids
A dispersion of one immiscible liquid into another through the use of a chemical that reduces the interfacial tension between the two liquids to achieve stability. Two emulsion types are used as muds: (1) oil-in-water (or direct) emulsion, known as an "emulsion mud" and (2) water-in-oil (or invert) emulsion, known as an "invert emulsion mud." The former is classified as a water-base mud and the latter as an oil-base mud.

Production Enhancement
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.

Heavy Oil
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 formation or treatment 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 both oil-in-water and/or water-in-oil emulsions. Such emulsions require temperature and chemical treating in surface equipment in order to separate.

Sediment Geology
The unconsolidated grains of minerals, organic matter or preexisting rocks, that can be transported by water, ice or wind, and deposited. The processes by which sediment forms and is transported occur at or near the surface of the Earth and at relatively low pressures and temperatures. Sedimentary rocks form from the accumulation and lithification of sediment. Sediments are classified according to size by the Udden-Wentworth scale.

Appraisal Geology
The phase of petroleum operations that immediately follows successful exploratory drilling. During appraisal, delineation wells might be drilled to determine the size of the oil or gas field and how to develop it most efficiently.

Exploration Geology
The initial phase in petroleum operations that includes generation of a prospect or play or both, and drilling of an exploration well. Appraisal, development and production phases follow successful exploration.