While there have been several good papers that describe the dissolution of Portland cement by hydrochloric:hydrofluoric acid (HC1:HF) solutions, no one has established a detailed comparative test procedure.1-3  The absence of a single, specific methodology left all parties to form their own interpretations of the acid solubility test described briefly in SPE 18986.

Discrepancies between the various procedures produced inconsistent results. Some laboratories were keeping the heated acid in glass vessels for extended periods before the cement specimen was introduced. Using glass vessels allows the HF to spend on the glass instead of the cement. Others were using grease on the curing molds and testing the cubes without adequate grease removal; this limits cement/acid contact. Different methods for agitating the acid and suspending the cement cubes in the acid were also being employed. One company was desiccating the specimens before acid immersion; another was using a complete inhibitor and surfactant package. Even the concentration and volume of acid was not universally agreed upon. All these factors must be controlled for an accurate comparison of data between different laboratories

Representatives from two operating companies have developed a jointly endorsed and very explicit methodology for conducting cement acid solubility tests. Equipment, chemicals, preparation methods and report forms were specified in extreme detail. This procedure was designed to address the above mentioned problems and yet be cost effective and applicable in any field lab.

Although the new test remains qualitative, it has provided consistent comparisons of conventional and microfine Portland cements. A quantitative method would require more costly, specialized equipment and limit field application.

This procedure provides a sound method for evaluating the relative acid solubility rates of various cement blends. It can also be used as a tool for developing improved cement designs or quality control procedures.

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