Consideration to Batch Mixing Time Improves API Recommendation for Testing Cement Slurries and Prevents Cement Failures: Lab Testing and Field Application

摘要

Batch mixing of cement slurries is a common exercise in the drilling operations. To simulate cement pump-ability of the cement API procedure are followed for thickening time. However, API Procedure does not consider batch mixing time in thickening time tests which can cause catastrophic results ending with cement failures. The objective of this paper is to show the importance of adding adequate time to mix the cement slurry with no pressure and temperature simulating batch mixing to the API thickening time tests. To the best of the authors’ knowledge this is the first study to investigate batch mixing time effect on cement thickening time. Laboratory testing invariably follows the API procedure for thickening time and, although this may be adequate in most cases, it cannot universally predict field behavior. Recently, several gas well cementing operations did not perform successfully causing expensive remedial operations due to immature cement setting. Initial lab testing in cement labs has shown acceptable thickening time using API procedure prior to the job and after the failure. Including batch mixing time to the cement with no temperature and pressure shorten the thickening time from 7 hours to less than 3 hours. This is due to the sensitivity of some high temperature retarders to shear rate used in cementing gas wells. The short thickening time was also observed when using these chemicals with tap water which rules out any possible contamination or bacterial effect. It is concluded from this study that adapting the batch mixing time into the API cementing procedure for all future wells will mitigate future cement failures. Future plan also will be to communicate with API committee to consider batch mixing time in cementing best practices.