David Watkins & Glen Roberts
A quality control survey of 162 acidizing fluids revealed the following problems: 1. Acid concentrations were often too high or too low. 2. Frequently, fluids were not thoroughly mixed. 3. In some cases, fluids contained incompatible additives. A field test kit and conventional laboratory analyses were used to determine the acid concentrations in fluids from 44 acid jobs done in Southern California during the last four years. On 41% of the jobs, the acid concentration of at least one fluid varied more than 30% from the specified value. The quality of the fluids from five service companies were surveyed; however, just two companies did 77% of the jobs. Analyses of iron content in the acids showed that 78% of the fluids contained less than 200 ppm iron. The average iron content was 180 ppm. The test kit assembled for this survey permits rapid well-site analysis by people who do not have formal training in chemistry. The total analysis time is about 2 minutes each for HCl and HF and 5 minutes for the iron analysis. The concentrations of HCl and HF are determined volumetrically by using constant volume dispensing bottles rather than a buret. A novel method is used to titrate for HF directly. A commercially available kit is used to measure the iron content of the fluids. The high percentage of jobs where acid concentration varied more than 30% from the specified value suggests that analysis of acid concentrations is a necessary part of any acidizing program. The test kit described here permits the simple and rapid analysis required for a successful quality control program.