Acid-removable damage

Sandstone acidizing is, for practical purposes, a method for removing acid-removable damage s) only. Except in rare cases, the production rate from an imdamaged well producing from a sandstone formation could be increased up to perhaps twice the original rate, at best. Acid-removable skin, discussed in detail in chapter 6, may manifest itself in the wellbore, in the perforations, or within the formation. 

Acid-removable damage may be present (or determined to be present), but the right type of acid must be used to remove the damage. For example, HCl will not dissolve plugging solids such as clays and other siliceous fines. HF should not be used to remove calcium carbonate solids or scales other than sihca. 

Add-removable formation damage can occur during any well operation. Table 6-1 summarizes types of acid-removable damage. HF mixtures can be used to remove the types of damage listed, unless otherwise noted. 

Oxalic acid is caustic and corrosive to humans. The seventy of symptoms associated with oxalic acid poisoning is related to the concentration and quantity ingested. Oxalic acid removes calaum in the blood, fonning calrium oxalate, and severe damage to the kidney may occur because of the insoluble caldum oxalate. 

A variety of antioxidants are added to food including vitamin C and vitamin E. Two antioxidants that may occasionally cause problems are butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), which have been associated with symptoms such as eczema, skin rash, runny nose, wheezing, headache, chest pain, flushing of the skin, and red eyes. At the same time, it has been reported that these antioxidants may be helpful in preventing cancer, possibly by removing damaging free radicals such as reactive oxygen and its by-products from fatty acids. 

The repair system removes damaged biomolecules before cell metabolism or viability has been altered due to their accumulation. Oxidatively damaged nucleic acids are repaired by specific enzymes, oxidized proteins are removed by proteolytic systems, and... 

One recent application in lEC consists of solid phase extraction disks which are used to eliminate matrix interference prior to analysis. The disk contains a membrane composed of resin beads enmeshed in a PTFE membrane, housed in a polypropylene housing. The resin is treated to remove specific ions such as H+ to remove hydroxide, Ag+ for excess halides and Ba to remove sulphate. Other disks such as hydroxide for acid removal and neutral styrene-divinylbenzene to eliminate hydrophobic components which can damage resin based IC columns are being developed [23]. 

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. 

Simply put, muscle size is determined by an intricate balance of musde protein synthesis and breakdown (Figure 6.1). Both processes are critical muscle protein synthesis makes new proteins while protein breakdown removes damaged ones. When synthesis of new proteins exceeds protein breakdown over time - due to increases in muscle protein synthesis, decreases in breakdown, or both - net protein balance is positive and muscle cell size increases. This is termed muscle hypertrophy. An increase in muscle cell size can easily be identified following a resistance exerdse training paradigm complemented with adequate nutritional intake (e.g., essential amino acids). Alternatively, when protein breakdown... 

Matrix acidizing has application in both carbonate and sandstone formations. In sandstone formations, matrix acidizing treatments should be designed primarily to remove or dissolve add-removable damage or plugging in the perforations and in the formation pore network near the wellbore. 

Identification of organic deposits is especially important in an acid treatment candidate well, because this damage is not acid removable. In fact, contact of organic deposits with add can create more severe (perhaps irreversible) damage. In addition, assessment and identification of organic... 

In a new well (or in a recompleted or reperforated well), if perforations are incomplete, then a positive skin value will be present. However, it is present as i pseudo-skin, not as skin due to acid-removable formation damage. The total skin effect may be written as equation (3.3), which refers to the large number of pseudo-skin factors that may exist, including phase- and rate-dependent effects partial completion and slant and incomplete perforations." In equation (3.3), s is the only skin that acidizing can address. 

Ascertain whether acid-removable skin damage is present. 

A well producing from a sandstone formation is a reliable candidate for acidizing only if acid-removable skin is present. With respect to add treatment design, it is important to determine not only whether damage (positive skin) is present but also, if it is, whether the damage can be removed with an acid treatment. 

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. 

It is the aim of sandstone acidizing treatments to reduce that portion of the total skin s) that is due to damage s). Skin damage must be present, but it must be acid removable, as manifested in the wellbore, in the perforations, and/or within the formation. In evaluating a well producing from a sandstone reservoir as a stimulation candidate, skin must be measured—or at the least, assessed as best as possible— to select the proper course of treatment (or nontreatment). 

Once it has been determined that acid-removable formation damage is present and that treatment is mechanically feasible, the proper acid type, acid volume, and acid concentrations must be determined. As mentioned earlier, the maximum-step conventional HF treatment design should be the starting point for design, eliminating those steps that are not necessary. The maximum-step procedure is given in table 6-2, with typical volumes per foot... 

Extremely damaged sandstones (very high acid-removable skin)... 

Candidates should be selected on the basis of the same principles as discussed earlier. In geothermal wells, the strongest indication of acid-removable formation damage is a sharp drop in the production rate. In a new well, poor production is the only indication. Well-testing techniques... 

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. 

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