Foamed acid

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. 

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

Foamed Acid Fracturing. The goal of add fracturing is to create a fracture within the reservoir and to etch the sides of the fradure face. Etching of the fracture face with add dissolves a portion of the fradure face and allows a conductive path to be created after the fradure has closed. The further the live add can reach into the fracture, the longer the conductive channel will increase well productivity. 

Methods of controlling foamed acid leak-off by creating a wallbuilding mechanism are possible. Alternating stages of cross-linked gelled water and foamed add increase the wall-building coeffident which influ-... 

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. 

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. 

In dolomite, add spends differently than in limestone formations. The readion of HC1 with dolomite is rate-limited at formation temperatures under 50 °C. Wormhole development, which is common in limestone acidizing, is not charaderistic in dolomite addizing (32). As pores become connected during matrix addizing operations, dolomites form caverns. The use of foamed acid ensures that the acid is spent in the primary channels and allows deeper penetration. Foams are good acid extenders. Deeper penetration can be achieved with foamed add as opposed to an equal volume of nonfoamed acid. 

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. 

In this low foaming acid cleaner 0.5% active of Phosphoteric T-C6 effectively hydrotropes the low foaming nonionic while other commonly used hydrotropes (such as Triton H-66, Dowfax 2A1,... 

Ridstone. [West Agio] Dairy low foam acid. 

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

Though synthetic detergents and acid inhibitors serve different purposes, both are large organic molecules that are attracted to surfaces. Synthetic detergents are attracted to oil water interfaces, where they promote wetting, emulsion formation, detergency, and foam. Acid inhibitors are attracted to metal surfaces, where they interfere with the chemical reaction of acid on metal. 

The foamed acid technique has been useful for arched tubes in condensers because the flow characteristics of the foam allow it to enter one end of each tube from one water box, fill the tubes completely, and emerge into an empty water box on the opposite end. 

The employment of foamed acid and acid-external emulsions (oil as the dispersed phase and gelled acid as the continuous phase) are other methods used to control the loss of acid solutions. The disadvantage of using oils is that a large concentration of oil is required to increase the viscosity of the emulsion formulation, which reduces the acid concentration and, therefore, the amount of acid available for fracture etching. Foaming the acid also reduces the amount of acid available for etching since less acid is present per unit volume injected. 

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... 

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. 

Adipic Acid n [ISV] (1877) (hexanedioic acid, 1.4-butanedicarboxylic acid) A dicarboxylic acid used in the production of polyamides, alkyd resins, and urethane foams. Esters of adipic acid are used as plasticizers and lubricants. It is used in the polymerization reaction to form nylon 66 polymers and in the manufacture of polyurethane foams Acid value, 767 molecular weight, 146.1 mp, 151°C and bp, 216°C/15mmHg. 

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. 

Quite often, acid will form predominantly single wormholes from limited numbers of perforations, without significant branching. That is the case with strong acids, such as HCl. Weaker acids, such as carbox)dic acids (e.g., acetic add), and retarded acid systems tend to create more branching of wormholes, which is desirable but only to a certain extent. Retarded acid systems include viscosified acids (e.g., polymer- or surfactant-gelled acid, emulsified acid, and foamed acid) or chemically retarded (surfactant-retarded) acid. The nature of wormholes created depends on injection rate, temperature, and formation reaction characteristics as well. 

Coiled tubing is a natural medium for injection of foamed acid or foam diversion. The smaller-diameter coil allows for maintenance of foam quality and stability during injection. This increases the chance of achieving diversion with foam, which is not often efficient or even possible. 

Retarded acid systems can extend the length and number of wormholes. Such systems include slightly gelled acid, chemically modified acid, surfactant-retarded acid, emulsified acid, and foamed acid. However, the time it takes for acid to spend is still short in most cases. Usually, only the formation near the wellbore can be treated effectively. Thus, effective uniform matrix treatment beyond several feet from the wellbore is exceptional. 

Viscous acid fracturing uses viscous acid systems such as gelled, emulsified, and foamed acid, or chemically retarded adds, to both create the fracture and differentially etch the fracture face. Treatments with viscous acid are applicable in heterogeneous carbonates such as dolomites or impure limestones. 

Foamed acid can be useful in increasing effective fracture length, as well as in improving contact in longer treatment intervals. Foamed acid is essentially a gas-in-add emulsion stabilized with a foaming agent. The amount of gas in the foam on a volume basis is called the quality for example, a foam composed of 70% gas and 30% liquid is a 70-quality foam. The gas phase is usually nitrogen, but CO can also be used. Most foamed acids are 60-75 quality. 

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. 

---