Detecting and treating cement and carbonate contamination of muds

Accurate quantitative detection methods for both cement and carbonate contamination currently exist. A test for souble calcium in a 7 to 8 pH range, supplemented by an analysis of temperature stability from consistometer readings is best for detecting cement contamination. The Garrett Gas Train has proven to be the most reliable method of detecting carbonates. The alkalinity methods for detecting carbonates generally overstate actual concentrations. The Pf-Mf method is particularly inaccurate for complex mud systems, and field tests have shown this method to indicate carbonate concentrations up to five times higher than the Garrett Gas Train reading. The alkalinity methods should only be used for qualitative identification and then only for relatively simple systems. Cement and carbonate contamination are very different in some respects, but there are similarities and interrelationships between the two which must be recognized. The basic reasons for their effects on rheology are quite different, but initial indicators, such as increased gel strengths, yield point and viscosities, are identical.