Acid Corrosion Inhibitors - Are We Getting What We Need?
- C.F. Smith (Dowell) | F.E. Dollarhide (Dowell) | Nancy J. Byth (Dowell)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 1978
- Document Type
- Journal Paper
- 737 - 746
- 1978. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 2.2.2 Perforating, 3.2.4 Acidising, 5.4.10 Microbial Methods, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.5 Offshore Facilities and Subsea Systems, 4.1.2 Separation and Treating, 4.3.4 Scale
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Acid corrosion-inhibitor test results are presented to demonstrate how data on inhibitor effectiveness can be misleading and why an industry-approved standard method must be developed. The corrosion rate of an acid system can be halved simply by increasing the acid-volume/steel-area ratio. Other variables affecting inhibitor performance are test pressure, time at temperature, chemical additives, test agitation, and type of steel.
The introduction in 1932 of the arsenic acid corrosion inhibitor (ACI) primarily was responsible for the development of well acidizing. Adding a chemical inhibitor such as arsenic reduces the rate of acid reaction with steel, but never completely stops the reaction under normal treating conditions. Therefore, the type and concentration of ACI needed to reduce the reaction rate to an acceptable level must be decided when planning an acid treatment. The most common factors affecting ACI requirements are bottom-hole temperature, exposure time, steel metallurgy, acid type and concentration, and surfactant use.
Acid corrosion inhibitors normally are evaluated in terms of metal loss resulting from exposure to a given type of acid at varying concentrations, temperatures, and exposure times. The most effective ACI concentration for a given set of conditions normally is obtained from this data. Testing methods thus lead to problems. Many critical acid treatments are decided on the basis of comparative inhibitor performance at high temperature. In less temperature-critical situations, treatment cost may be reduced by using a cheaper ACI or a lower-concentration one to give minimum desired protection. Unless test data from different sources are obtained with standard test procedures, a true comparison of ACI performance is impossible. performance is impossible. In spite of organized efforts, no standard test procedure exists today. Typically, the term "acceptable corrosion rate" is arbitrary and varies among companies. Also, as the standard changes so do temperature ranges. Table 1 is an example of this variation. Table 1 indicates that ACI performance requirements are less rigid at higher performance requirements are less rigid at higher temperatures. The question then is "Why should corrosion be more acceptable at higher temperatures?"
Actually, the entire method of comparing ACI performance is vague and ambiguous. Data for inhibitors can be performance is vague and ambiguous. Data for inhibitors can be obtained only by designing special tests that fail to simulate treating or down-hole conditions. Frequently, critical decisions are made using this data. This study points out the effect of test conditions on inhibitor performance so that acidizing treatment designers can understand real performance limits on ACI systems better and can select performance limits on ACI systems better and can select the best inhibitor for existing well conditions. Some cases involve weighing performance claims with how the data was obtained.
The comparative effectiveness of an ACI can be judged only in terms of laboratory simulations. Simulation quality becomes the primary factor in judging ACI performance. Thus, we must look at test conditions that performance. Thus, we must look at test conditions that generate data affecting inhibitor choice and point out the need for better simulation of well conditions. Also, we must develop standards and test procedures that are uniform throughout the industry so that ACI performance data truly is comparative.
Several years ago, the API-NACE Subcommittee on Corrosion Testing began to develop a standard test method and equipment. The test procedure and cell specifications are scheduled for release in 1978.
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