On-Site Diagnosis of Cement Job Problems: The Concept of Job Signatures

Abstract

Summary Since the introduction of free-fall models for primary cementing, several companies have been monitoring cementing operations by continually measuring the rate of returns, the rate of pumping, the density of the fluids pumped, the density of the fluids returned to the surface, and the surface pressure.' Measured values of surface pressure and rate of returns have been compared to predicted values obtained with cementing simulators. 1–7 Discrepancies between measured and simulated behaviors that cannot be explained as normal simulation and job measurement limitations are attributed to problems that develop during the cementing operation. Although problems have been detected by this approach, in some cases it has not been possible to ascertain the exact cause of the misbehavior. Therefore, proper and timely corrective adjustments have not always been made during the job. To improve our ability to diagnose cement job problems while the cement job is in progress, we investigated six potential job problems with a cement job simulator that includes free fall. The job problems were channeling, unsuspected (unmeasured) washout, lost circulation, influx, flow restrictions, and slurry dehydration. Representative graphs show the behavior trends for each of the six potential cement job problems. The graphs show the normal (without trouble) behavior and the departure from the norm for the problem situation. Lists of generalized "job signatures" for each case are also given. Characteristics that are considered the main indicators of each job problem are highlighted. Three field cases illustrate how the concept of job signatures can be used effectively to assist in detecting potential job problems during the actual job.