Foamed acid fluids

Desirable foams Foam drilling fluid Foam fracturing fluid Foam acidizing fluid Blocking and diverting foams Gas-mobility control foams... 

Foamed acid fluids were developed to control accelerated leak-off without the addition of fluid loss additives. Foams are clean fluids and therefore less damaging. Because foams are not wall-building fluids, leak-off control is not affected by fracture face erosion because of the presence of acid. 

Foam fracturing and stimulation fluids Foam acidizing fluid Gas well unloading foam... 

Gas/Liquid Systems Producing oilwell and well-head foams Oil flotation process froth Distillation and fractionation tower foams Fuel oil and jet fuel tank (truck) foams Foam drilling fluid Foam fracturing fluid Foam acidizing fluid Blocking and diverting foams Gas-mobility control foams... 

Acid-in-oil emulsion can extend the propagation of acid considerable distances into a reservoir because the continuous (oil) phase prevents or minimizes contact between the acid and the rock [4,678,689]. Emulsification also increases viscosity and will improve the distribution of the acid in layered and heterogeneous reservoirs. Acidizing foams are aqueous, in which the continuous phase is usually hydrochloric acid (carbonate reservoirs) or hydrofluoric acid (sandstone reservoirs), or a blend, together with suitable surfactants and other stabilizers [345,659]. Foaming an acidizing fluid increases its effective viscosity, providing mobility control when it is injected [678]. 

A foam, aqueous or non-aqueous, that is injected into a petroleum reservoir to improve the productivity of oil- or gas-producing wells. Some mechanisms of action for foam stimulation fluids include fracturing, acidizing to increase permeability, and diversion of flow. 

Cocamidopropyl betaine and cocamidopropyl hydroxysultaine, discussed later, are also used in petroleum production. Their relatively high foaming nature, electrolyte tolerance and hydrolytic stability make them useful for foam acidizing and foam fracturing fluids. 

The investigations (26—29) illustrated the difference between reactive and nonreactive foams. During the tests, core permeabilities ranged from 0.5 to 5.0 md. Fluid loss of the nonreactive foam was approximately half of the reactive foam, although the stability of each did not show a significant difference. This result suggests two possible scenarios. The first is that the foamed acid is destabilized in its reaction with limestone, and this destablization causes greater fluid loss of the gas phase. The second is that the permeability is increased as the add dissolves the limestone. 

Field results are inconclusive as to the mechanism that controls fluid loss of the reactive foams. In certain situations, improvement in productivity has been gained by using foamed add instead of conventional add treatments. However, many field applications of foamed acid show no stimulation benefit over conventional acid treatments. 

One primary benefit of using a foamed acid in a matrix application is the use of the energy for faster cleanup of the undissolved fines created during the treatment. The benefits realized by using a foamed add treatment fluid are very similar to those benefits gained from using nonreactive foamed fluids. Foamed acids use a smaller volume of add than conventional add treatments, and deeper penetration into the formation is attained. Thus a reduction in the volume of add pumped would reduce the cost of products to attain the same productivity gain. However, equipment costs would then increase because of the use of gas transports and pumpers. 

Brine foams in certain circumstances are more acceptable as diversion fluids than add foams, as shown in Tables III and IV. The data illustrate that either high-porosity or high-permeability limestones reacted with the foamed acid to create poor diversion charaderistics. Foam brines that will not react with the carbonate formation produced better diverting fluids. 

Thompson and Gdanski (34) also performed dual-core experiments to determine the best diversion method using foam, and the maximum permeability difference needed to achieve an equal flow rate through the core. Multiple diversion techniques were used, including foamed acid, multiple stages of foamed add, and various qualities of foamed brine. The tests showed that foamed brine reduced flow rates better than foamed add. Also, higher quality foamed brines were most effective. In order to effectively use foamed diversion fluids, the permeabilities of the zones of interest must be relatively similar. The limit on permeability differences is approximately a factor of 10. Otherwise, the more permeable zone will accept both the diversion and treatment fluids. 

Well Site Safety. Containment of a foam drilling fluid into a closed loop system provides a measure of safety that open systems do not allow. Hydrocarbons, acid gases and oxygen depleted air are kept safely away from personnel. Additionally, open foam pits can create a hazard, as they are typically plastic lined pits, that could allow the unknowing person to slip in and possibly suffocate under a blanket of foam. 

Food contains one polysaccharide (starch) and three disaccharides (maltose, sucrose, and lactose). Salivary and pancreatic amylase digests starch to yield maltose and sucrose, and lactose to yield maltose and sucrose. Sucrose, maltose, and lactose are split by invertase, maltase, and lactase, respectively. The products of the disaccharidase reactions are fructose, glucose, and galactose. Whenever amylase or one of the disacchari-dases is absent from the intestinal content, the undigested sugars pass in the lower part of the intestinal tract and are fermented by the bacterial flora. As a result, lactic acid and volatile acids are formed and stimulate peristalsis and fluid secretion by the intestinal mucosa. Liquid foaming acid and foul-smelling feces are emitted. Amylase may be absent in pancreatic disease. Inborn errors characterized by the absence of intestinal lactase, maltase, and invertase have been described. 

In the 1980s and into the 1990s, developments in sandstone acidizing addressed treatment execution more than fluid chemistry. Techniques included nitrified and foamed acid treatments, high-rate/high-volume HF acidizing, and CO -enhanced HF acidizing. These are discussed in later chapters. 

Diverter choices are also limited. Ball sealers are usually not effective in horizontal wells, because they tend to the bottom side of the pipe. Foam diversion can be effective, to some extent. In any case, it is known that any attempt to divert acid fluids with a nondamaging diverter is better than no diversion at all. 

The downside to foamed acid is the reduced amount of acid available per unit volume of fluid. In practice, this is often partially compensated for by using higher-strength acid, such as 28% HCl. 

Physically retarding acid reaction is accomphshed by thickening (viscosifying) the acid used. Viscous acids include polymer-gelled, surfactant-gelled, emulsified, and foamed acids. Combinations can also be used in addition, surfactant-retarded acid can be gelled or foamed. The intent of viscosifying acid is to slow the rate of acid diffusion outward, to the rock surfaces, and to reduce the rate of fluid loss from wormhole to unreacted matrix. Both of these effects work to increase live acid penetration distance. 

Foamed acids can be effective in improving contact with longer treatment intervals. As in fracture acidizing, most foams are 60-75 quality. The lightness of foam makes it an effective stimulation fluid for damaged gas wells. As with emulsions, the pumping of foam at high rates is not always possible. 

C. W., and B. D. Miller. 1974. New, low viscosity acid in oil emulsions. Paper SPE 5159, presented at the Society of Petroleum Engineers National Meeting and Exhibition, Houston. Ford, W. G. F. 1981. Foamed acid—an effective stimulation fluid. Journal of Petroleum Technology. July 7. 

Polystyrene. Polystyrene [9003-53-6] is a thermoplastic prepared by the polymerization of styrene, primarily the suspension or bulk processes. Polystyrene is a linear polymer that is atactic, amorphous, inert to acids and alkahes, but attacked by aromatic solvents and chlorinated hydrocarbons such as dry cleaning fluids. It is clear but yellows and crazes on outdoor exposure when attacked by uv light. It is britde and does not accept plasticizers, though mbber can be compounded with it to raise the impact strength, ie, high impact polystyrene (HIPS). Its principal use in building products is as a foamed plastic (see Eoamed plastics). The foams are used for interior trim, door and window frames, cabinetry, and, in the low density expanded form, for insulation (see Styrene plastics). 

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