Acid treatment concentration guidelines

Selection of acid concentrations must be based on the formation characteristics. Knowledge of permeability, porosity, and mineralogy is imperative. Amounts and types of clays and feldspars are especially important to ascertain. This information can be obtained through X-ray diffraction analysis. 

Nevertheless, the location of minerals is of greatest importance. Scanning electron microscopy (SEM) and thin-section analysis are additional tools that are useful in identifying locations of quartz, clays, feldspars, carbonates, and other minerals. These are all factors considered in acid treatment design. Expertise is available through the major service companies, who should be contacted to help in treatment development. Input from company geologists should also be sought. 

In 1984, McLeod introduced his acid-use guidelines to the industry. This was a breakthrough in formation-based acid treatment design. The original guidelines focused on mineralogy, which was—and still is—often overlooked. McLeod s guidelines are shown in table 6-5. 

High iron carbonate 5% NH CI + 3% acetic acid 15% HCIt + iron control  

High iron chlorite clay ( 5%) 10% Acetic acid + 5% NH CI 10% Acetic acid-0.5% HF 

---

Little has been published in support of acidizing with high-concentration HF, which opposes conventional guidelines. However, there is some evidence that high-concentration HF treatments can be effective in certain sandstone formations. 

---