Invert emulsions

Water-in-OilEmulsions. A water-in-od or invert emulsion consists of a continuous od phase which surrounds finely divided water droplets that are uniformly dispersed throughout the mixture. The invert emulsion ensures that the od is in constant contact with the hydrauHc system s moving parts, so as to minimise wear. 

The fluid is formulated from a premium mineral od-base stock that is blended with the required additive to provide antiwear, mst and corrosion resistance, oxidation stabdity, and resistance to bacteria or fungus. The formulated base stock is then emulsified with ca 40% water by volume to the desired viscosity. Unlike od-in-water emulsions the viscosity of this type of fluid is dependent on both the water content, the viscosity of the od, and the type of emulsifier utilized. If the water content of the invert emulsion decreases as a result of evaporation, the viscosity decreases likewise, an increase in water content causes an increase in the apparent viscosity of the invert emulsion at water contents near 50% by volume the fluid may become a viscous gel. A hydrauHc system using a water-in-od emulsion should be kept above the freezing point of water if the water phase does not contain an antifreeze. Even if freezing does not occur at low temperatures, the emulsion may thicken, or break apart with subsequent dysfunction of the hydrauHc system. 

Oilfield Uses. Calcium chloride has two uses in the oilfield as a primary ingredient in completion fluids and as the brine phase in an invert emulsion oil mud. An excellent review of oil well drilling fluids is available (36) (see also Petroleum, drilling fluids). 

Emulsions. Emulsions are formed when one liquid is dispersed as small droplets in another liquid with which the dispersed liquid is immiscible. Mutually immiscible fluids, such as water and oil, can be emulsified by stirring. The suspending liquid is called the continuous phase, and the droplets are called the dispersed (or discontinuous) phase. There are two types of emulsions used in drilling fluids oil-in-water emulsions that have water as the continuous phase and oil as the dispersed phase, and water-in-oil emulsions that have oil as the continuous phase and water as the dispersed phase (invert emulsions). 

Oil-Base Muds. Oil-base muds contain oil as the continuous phase and water as the dispersed phase. Oil-base muds contain less than 5% (by volume) water, while oil-base emulsion muds (invert emulsions) have more than 5% water in mud. Oil-base muds are usually a mixture of diesel fuel and asphalt the filtrate is oil. 

Figure 4-113. Approximate rheology of two oil-based mud systems. (VERTOIL = invert emulsion of oil and CaClj brine OILFAZE = invert emulsion of oil and freshwater)...

A wellbore fluid has been developed that has a nonaqueous continuous liquid phase that exhibits an electrical conductivity increased by a factor of 10 to 10 compared with conventional invert emulsion. 0.2% to 10% by volume of carbon black particles and emulsifying surfactants are used as additives. Information from electrical logging tools, including measurement while drilling and logging while drilling, can be obtained [1563]. 

Esters of Q to Cn monocarboxylic acids [1288-1292], acid-methyl esters [1282], and polycarboxylic acid esters [1287], as well as oleophilic monomeric and oligomeric diesters [1293], have been proposed as basic materials for inverted emulsion muds. Natural oils are triglyceride ester oils [1844] and are similar to synthetic esters. Diesters also have been proposed [1293-1297]. 

Acetals and oleophilic alcohols or oleophilic esters are suitable for the preparation of inverted emulsion drilling muds and emulsion drilling muds. They may replace the base oils, diesel oil, purified diesel oil, white oil, olefins, and alkylbenzenes [825,826]. Examples are isobutyraldehyde di-2-ethylhexyl acetal dihexyl formal and mixtures with coconut alcohol, soya oil, and a-methyldecanol. 

Other Materials for Inverted Emulsion Drilling Fluids... 

Nitrates and nitrites can replace calcinm cMoride in inverted emulsion drilling muds [612],... 

N. Monfreux, P. Perrin, F. Lafuma, and C. Sawdon. Invertible emulsions stabilised by amphiphilic polymers and application to bore fluids (emulsions inversables stabilisees par des polymeres amphiphiles et application a des fluides de forage). Patent WO 0031154, 2000. 

H. Muller, C. P. Herold, and S. von Tapavicza. Monocarboxylic acid-methyl esters in invert-emulsion muds (Monocarbonsaure-Methylester in Invert-Bohrspiilschlammen). Patent EP 382071,1990. 

M. Santhanam and K. Macnally. Oil and oil invert emulsion drilling fluids with improved anti-settling properties. Patent EP 1111024-A, 2001. 

S. Young and A. Young. Recent field experience using an acetal based invert emulsion fluid. In Proceedings Volume. IBC Tech Serv Ltd Prev of Oil Discharge from Drilling Oper— The Options Conf (Aberdeen, Scotland, 6/15-6/16), 1994. 

These are usually mineral oils or synthetic basestocks containing a complex mixture of additives including corrosion inhibitors, extreme pressure additives and emulsifiers. They are almost exclusively oil-in-water emulsions, although in rare instances, invert emulsions may be used. They are normally used between l%-20% emulsions depending on the application. As these products are water extendible, they are subject to attack by micro-organisms. As a consequence, they are often formulated with one or more preservatives. 

An emulsion separation method using hydrocyclones. The emulsion comprises a continuous phase, a discontinuous phase and fine solid particles. In the first step, the original emulsion is separated into an overflow emulsion and an underflow emulsion, in a first hydrocyclone. The overflow emulsion comprises portions of the continuous phase, the discontinuous phase and the fine solid particles. The overflow emulsion is inverted in which the continuous phase of the overflow emulsion is now a second discontinuous phase and the original discontinuous phase becomes a second continuous phase. Then, the inverted emulsion is directed to one or more subsequent hydrocyclones and the second continuous and discontinuous phases are collected. The fine solid particles remain in the second discontinuous phase. 

Figure 1.30. Evolution of the water phase viscosity rjc as a function of the shear rate and alginate concentration (filled symbols). For the sake of comparison, the viscosity rja of the inverted emulsion at 0, = 75 wt% is reported in the same graph (open symbols). (Adapted from [162].)...

The primary W/O emulsion was diluted to vary the mass fraction tpi of the water droplets in the inverted emulsion. In Fig. 1.32 the evolution of the globule diameter... 

The cross-section of the heads when dissolved in water —COOCs, —COOK, —COONa are evidently greater than the cross-section of the hydrocarbon oleate chain, whilst the head —COOAg is smaller than the chain since the invert emulsion is produced. Similarly the groups... 

In a typical SBM, the chemicahwater volume ratio is 70 30 [27]. Water is usually in the form of CaCl2 brine and is dispersed in the oil to form a water-in-organic phase mixture called an invert-emulsion. It promotes dehydration of shales in the formation being drilled [5]. 

Emulsifiers and wetting agents (detergents and/or surfactants) are composed of anionic, cationic, or nonionic detergents, metal soaps, polyamines, and tall oils or fatty acids [28]. They facilitate the formation of a stable dispersion of insoluble liquids in water (invert-emulsion). Wetting agents are used to ensure that the solids in mud... 

Tan, C. P., Drummond, C. J., Mody, F. K., and Tare, U. A. (2002). High membrane efficiency water-based drilling fluids Alternatives to invert emulsion fluids for drilling troublesome shale formations. In SPE Asia Pacific Oil and Gas Conference and Exhibition, Melbourne, Australia. 

A petroleum industry term used to denote an oil-in-water emulsion (most well-head emulsions are W/O). Reverse emulsion has the opposite meaning of the term invert emulsion . See also Invert Emulsion. 

Mixture of two liquids which are not to miscible with each other, e.g., oil-in-water cutting fluid. Water-in-oil is classified as an inverted emulsion. The emulsions droplets are typically 1000 nm size. Soft-core reverse micelles size 10 to 20 nm.. 

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