Demulsification is the breaking of a crude oil emulsion into oil and water phases. A fast rate of separation, a low value of residual water in the crude oil, and a low value of oil in the disposal water are obviously desirable. Produced oil generally has to meet company and pipeline specifications. For example, the oil shipped from wet-crude handling facilities must not contain more than 0.2% basic sediment and water (BS&W) and 10 pounds of salt per thousand barrels of crude oil. This standard depends on company and pipeline specifications. The salt is insoluble in oil and associated with residual water in the treated crude. Low BS&W and salt content is required to reduce corrosion and deposition of salts. The primary concern in refineries is to remove inorganic salts from the crude oil before they cause corrosion or other detrimental effects in refinery equipment. The salts are removed by washing or desalting the crude oil with relatively fresh water. Oilfield emulsions possess some kinetic stability. This stability arises from the formation of interfacial films that encapsulate the water droplets.
Micelles [mi-sel] (singular "micelle"), or micellae (singular "micella"), are spherical clusters of hydrocarbon molecules that act as emulsifying agents. Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible. The process of forming micelles is known as micellisation and forms part of the phase behaviour of many lipids according to their polymorphism. Micelles form when the polar head and the non polar tails arrange in a special way.
Phase behavior plays an important role in a variety of enhanced oil recovery (EOR) processes. In surfactant/polymer displacement processes, the effects of capillary forces are reduced by injection of surfactant solutions that contain molecules with oil- and water-soluble portions. Such molecules migrate to the oil/water interface and reduce the interfacial tension, thereby reducing the magnitude of the capillary forces that resist movement of trapped oil. In these ternary diagrams, the components shown are no longer true thermodynamic components because they are mixtures. A crude oil contains hundreds of components, and the brine and surfactant pseudocomponents also may be complex mixtures.
Understanding how foams behave and perform in porous media is critical to the effective application of foams for conformance improvement applications in matrix-rock reservoirs. How foam exists and functions in porous media is not always intuitively obvious on the basis of how foam behaves in bulk form (e.g., when existing in a bottle). In addition to the properties of bulk foams, which for the most part, are applicable to foam that resides in porous media, there are two specialized properties of foams that reside in porous media. In general, foams in matrix rock pores do not exist as a continuous interconnected liquid/film structure that contains gas bubbles, as is the case for a bulk foam. Foam in porous media exists as individual gas bubbles that are in direct contact with the wetting fluid of the pore walls.
Many crudes contain dissolved waxes that can precipitate and deposit under the appropriate environmental conditions. These can build up in production equipment and pipelines, potentially restricting flow (reducing volume produced) and creating other problems. This page discusses how to anticipate, prevent, and remediate wax problems in production. Paraffin wax produced from crude oil consists primarily of long chain, saturated hydrocarbons (linear alkanes/ n-paraffins) with carbon chain lengths of C18 to C75, having individual melting points from 40 to 70 C. This wax material is referred to as "macrocrystalline wax."
Two forms of derivatized cellulose have been found useful in well-cementing applications. The usefulness of the two materials depends on their retardational character and thermal stability limits. This is commonly used at temperatures up to approximately 82 C (180 F) for fluid-loss control, and may be used at temperatures up to approximately 110 C (230 F) BHCT, depending on the co-additives used and slurry viscosity limitations. Above 110 C (230 F), HEC is not thermally stable. HEC is typically used at a concentration of 0.4 to 3.0% by weight of cement (BWOC), densities ranging from 16.0 to 11.0 lbm/gal, and temperatures ranging from 27 to 66 C (80 to 150 F) BHCT to achieve a fluid loss of less than 100 cm3 /30 min.
Included are applications of foam for mobility control and for blocking gas. In 1989, Hirasaki reviewed early steam-foam-drive projects. In 1996, Patzek reviewed the performance of seven steam-foam pilots conducted in California. Early and delayed production responses were discussed for these pilots. Gauglitz et al. review a steam-foam trial conducted at the Midway-Sunset field of California.
Wax precipitation may result in wax deposition in tubing, pipelines and other production equipment. This deposition can pose significant flow problems requiring remediation. This page discusses the problems created by wax deposition and available methods for remediating those issues. Crystallization of waxes in crude oils leads to non-Newtonian flow characteristics, including very high yield stresses that are dependent on time and the shear and temperature histories of the fluid. Wax precipitation-induced viscosity increases and wax deposition on pipes are the primary causes of high flowline pressure drops.
Bentonite is not typically used as the primary fluid-loss agent in normal-density slurries. In low-density slurries, where higher concentrations can be used, it may provide sufficient fluid-loss control (400 to 700 cm 3 /30 min) for safe placement in noncritical well applications. Fluid-loss control, obtained through the use of bentonite, is achieved by the reduction of filter-cake permeability by pore-throat bridging. Microsilica imparts a degree of fluid-loss control to cement slurries because of its small particle size of less than 5 microns. The small particles reduce the pore-throat volume within the cement matrix through a tighter packing arrangement, resulting in a reduction of filter-cake permeability.
Bulk foam, as found in the head of a glass of beer or as found in association with cleaning solutions, is a metastable dispersion of a relatively large volume gas in a continuous liquid phase that constitutes a relatively small volume of the foam. Foams for use in conformance improvement are dispersions of microgas bubbles usually with diameters/lengths ranging between 50 and 1000 μm. Foam in porous media exists as individual microgas bubbles in direct contact with the wetting fluid of the pore walls. These microgas bubbles are separated by liquid lamellae that bridge the pore walls and form a liquid partition on the pore scale between gas bubbles. Foam propagates in most matrix reservoir rock as a bubble train in which each gas bubble is separated from the next by a liquid lamellae film.