Addization

Acid fracturing, friction reducers, 15 Acid hydrolysis, lignin, 173 Acid injection into carbonate reservoir, 610-611 Acid-rock reactions, rate, 15,16 Add wormholing in carbonate reservoirs, 608-620 in carbonate rocks, 610-611 Acidity-controlled redox reactions, 141-142 Addization... 

Foamed Matrix Acidizing. Matrix addizing is a stimulation treatment used to remove damage near the wellbore without deating a fracture. The process involves the injection of a reactive fluid into the porous medium at a pressure below the fracturing pressure. The fluid dissolves some of the porous medium and consequently increases its permeability. 

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. 

Play with the tempo (see the next section) when AdDizing a media file to get it to fit... 

Herman Frasch, the chief chemist of the Solar Refinery at that time, is credited with the invention of the addizing technique. Frasch was issued the first patent on acidizing on March 17, 1896. This was the first great milestone in the history of acidizing. The brief Frasch patent was the first of many acidizing patents. In the patent, Frasch proposed... 

As it turned out, the Frasch patent was the more successful. HCl reacts in limestone to form the soluble products carbon dioxide (CO ) and calcium chloride (CaCl ). These products could be produced out of the formation once a treated well was returned to production. In contrast, sulfuric acid produces insoluble calcium sulfate (CaS04), which could plug the formation. Therefore, Frasch is credited with the invention of addizing. 

If a well is not damaged or if it is but the damage is not acid removable, then there should be little to no expectation from an addizing treatment. Such a well should not be acidized. This is because addizing does not decrease skin much below zero, as can be shown from the radial-flow mathematics. However, an undamaged well may respond to hydraulic fracturing, or short skin bypass fracturing, if feasible from both a mechanical and a reservoir standpoint. 

Comparison of production rates (before and after acid treatment) is the most obvious and simple measure of success. Rate comparison should be made only after all spent acid has been returned and well production has retmned to formation fluids only. Changes in oil-to-water or gas-to-water ratios are important to monitor. Addizing should not preferentially stimulate a water zone. If that happens, it may be that the reservoir was not understood or that diversion was not effective. 

Damage bypass (matrix acidizing and fracture addizing)... 

Design simulation. Commercial software programs exist that model the processes of fracture addizing. They use the same fundamental prediction methods used in simulation of hydraulic fracturing with nonreactive fluids. Modifications for add reaction kinetics, among other parameters, are included in modules for simulation of fracture acidizing. Settari has provided an example with discussion. ... 

As previously discussed, the most common purpose of matrix addizing is to restore near-wellbore permeability in or through a damaged formation zone. Because it is bypassed, rather than directly removed, formation damage in a candidate for carbonate acidizing need not be acid removable by contrast, it does need to be add removable in a candidate for sandstone acidizing. 

This chapter discusses conventional procedures for matrix addizing procedures, as well as alternative and retarded acid methods, additives, and add placement. Appendix B includes examples of successful procedures using matrix acidizing. 

It is important to evaluate the effectiveness of every stimulation treatment. Evaluations of matrix addizing and add fracturing treatments are usually based on production increases or comparison with other wells. With matrix acidizing, comprehensive pretreatment and posttreatment well testing and interpretation are usually not economically justified. Comprehensive evaluation can be justified most of the time with acid fracturing and propped fracturing. 

Sometimes this is left undone, especially when there is a race against the clock to complete a treatment. Advanced planning is essential, to avoid such oversights. Flowing an addized well as soon as possible, with minimal delay, is an underrated concern in sandstone addizing. 

Fines are generated during sandstone addizing and are carried more efficiently by more viscous or more dense spent acid mixtures. To avoid potentially damaging effects, the flow rate should be set low at first. Then, after spent add is produced back, the flow rate should be gradually stepped up to planned production conditions. 

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