SELECT ACID CAPS are primarily used in water injection wells to remove carbonate scale and rust deposits and lower injection pressures. Injection pressure drops of several hundred PSI have been observed following ACID CAP treatments. Some wells have gone on vacuum and taken water by gravity. Success has also been experienced in some producing oil wells, gas wells and water supply wells.

SELECT ACID CAPS, after removing the plastic wrapper, are dropped directly into the well or introduced to the system through the water supply tank. Dropping the stick directly into a well is best because not as much dilution will occur. In a well with tubing obstructions or small valve openings, ACID CAPS may be successfully used by first dissolving the sticks in fresh water and then pumping or pouring the solution into the well.

ACID CAPS are very economical (as compared to conventional scale removal operations) and can eliminate or delay the need for HCl acid treatments. Continuous treatment with ACID CAPS (especially after a conventional acid or clean-out job) can extend the time period between future scale removal operations. ACID CAPS are less corrosive to steel pipe than conventional liquid HCl acid jobs, because most of the acid generated by the stick is released down-hole. Conventional liquid HCl acid reacts with the steel, rust and scale inside the pipe all the way down the well.

ACID CAPS are safe to handle and easy to use by less experienced field personnel; however, like all acids, contact with eyes or skin should be avoided. The plastic protective wrapper when removed before dropping stick can be used as a protective glove while handling the stick. ACID CAPS are safe to use in cement lined tubing and plastic line pipe. Continued treatments over long periods of time through a by-pass feeder into cement lined pipe should be avoided.


The number of SELECT ACID CAPS to be used is based on the number of feet of perforated interval or open hole and severity of scale build-up. Field tests indicate the best results were achieved by using large initial slug treatment (1.8 to 5.4 lbs of stick per foot of interval) followed by smaller periodic treatments (about half of the initial slug amount).

JUNIOR (1 ¼” X 18”)1 to 2 Sticks per 1 BBL of water
JUNIOR (1 ¼” X 15”)2 to 4 Sticks per 1 BBL of water


A REACTIVE EQUIVALENCY of ACID CAPS vs. HCL ACID RATIO was determined by field tests. These tests indicated that about 10 ACID CAPS (1 ¼” X 15”) dropped in an injection well, resulted in an equivalent pressure drop, as did using 120 gallons of 15% HCl acid. Liquid HCl acid loses strength by reacting on the steel, scale and rust inside the pipe all the way down the well while the sticks release most of their acid down-hole.


Shut-in the well, first remove the plastic wrapper and then drop sticks through a lubricator and return well to injection. This procedure is best for open-hole, no rat-hole, low rate wells, or wells deeper than 3,300 feet. FOR SHALLOW PERFORATED WELLS WITH RAT-HOLE drop sticks and leave well shut-in about 15 minutes or until sticks fall to the perforations (whichever occurs first) then return well to injection. The time in minutes for the sticks to fall to the perforations in a shut-in well is equal to the depth of perforations divided by 110. (Time,min = Depth,ft / 110)


The stick will normally dissolve in 20 to 80 minutes (in moving water or when falling through water) depending on temperature, salt content and relative water motion. ACID CAPS are 100% soluble in water. The melting point of the stick is 145ºF. The stick will dissolve in water in wells with BHT below 145º (just at a slower rate). Lab tests indicate the dissolving rate in 50,000 PPM moving brine water to be 105 minutes @ 100º, 38 minutes @ 120º, 7 minutes @ 140º, and 2 minutes @ 180º. If slowing the dissolving rate is desired, coat ACID CAPS with oil or grease. The specific gravity is 1.23. The falling rate through fresh water is approximately 110 feet per minute. Gas moving up tubing will often change falling characteristics.


JUNIOR (1 ¼” X 18”)36/caseNA72/chest
JUNIOR (1 ¼” X 15”)36/case45/pail72/chest


As with all industrial chemicals, contact with eyes or skin should be avoided (see MSDS). Wash thoroughly with water. Sticks should be stored in a cool dry place. Always remove stick from plastic bag before using. Bag can be used as a glove to avoid contact.


The information in this bulletin is believed to be accurate, however all recommendations are made without warranty since the conditions of use are beyond Select Industries, Inc. control. Select Industries, Inc. disclaims any liability in connection with the use of the information, and does not warrant against infringement by reason of the use of any of its’ products in combination with any other material or in any process.