On-Site Acidizing Fluid Analysis Shows HCl and HF Contents Often Varied Substantially From Specified Amounts

Abstract

Summary A quality-control survey of 162 acidizing fluids revealed the following problems. problems.Acid concentrations were often too high or too low.Frequently, fluids were not thoroughly mixed.In some cases, fluids contained incompatible additives. A field test kit and conventional laboratory analyses were used to determine the acid and iron concentrations in fluids from 44 acid jobs in southern California over a 4-year period. Results of the survey suggest that analysis of acid concentrations would enhance the quality of acidizing programs. The kit described here permits the simple and rapid analysis programs. The kit described here permits the simple and rapid analysis that would contribute to a quality-control program. Introduction Acidizing fluids are the product of research and field experience. Although laboratory tests contribute to the design of acidizing fluids, field tests and experience determine the final fluid composition. Once a fluid appears to work, it will be used routinely in a specific field. Routine use, however, does not ensure good acid quality. These fluids are complex mixtures that contain several critically active chemicals. One fluid may contain HCl, HF, acetic acid, corrosion inhibitor, antisludging agent, foaming agent, solvent or mutual solvent, sequestering agent, and other chemicals. Each one contributes a specific function and must be compatible with the others. The presence of these additives in proper concentration is always critical. Therefore, we initiated a quality-control program for acids used in southern California. Our objective is to obtain the fluids we specify bychecking acid quality on the job to prevent the use of poor-quality fluids,defining quality control problems so they can be solved, andgiving the acid suppliers more incentive to control the quality of their fluids. This paper presents the results of a 4-year quality control survey and a description of the kit used to analyze the fluids. Description of the Acid Quality Test Kit The test kit (see Fig. 1) permits rapid analysis of HF, HCl, and iron concentrations. Plastic labware is used almost exclusively in the kit to avoid the inconvenience of breakage in the field and to avoid contact of HF with glass. The HCl and HF concentrations in weight percent are determined by titration. Samples are titrated by using constant-volume dispensing bottles rather than a buret. These bottles accurately and reproducibly dispense 1-mL (1-cm3) quantities of the titrating solution; therefore, the analytical result is a concentration range rather than a discrete concentration. This range spans 0.4% for HF and 0.91% for HCl in the absence of HF. For example, in the HF titration each milliliter of titrating solution represents 0.4% of HF. If six 1-mL (1-cm3 ) quantities of the solution are required to reach the endpoint, the HF concentration is known to be between 2.0 and 2.4%. JPT p. 865