Cementing operations represent one of the more critical aspects concerning well integrity. Despite the large amount of research and the huge number of operations throughout the years, the industry still faces well-integrity problems during and after cementing operations. These occurrences have been experienced by the petroleum industry worldwide and can happen at any moment of the well life cycle, from the drilling phase to abandonment after the well’s production life. Here, I have categorized these well-integrity issues according to the moment at which they manifest: during the cement displacement inside the well (minutes); after the cement placement (hours to days), and after the cement has been cured (months to years).
The first category may result in serious well-control problems, including blowouts (the Macondo blowout was related to cementing operations). According to a survey published by the former Minerals Management Service, during the period between 1992 and 2006, the leading factor contributing to blowouts in the US offshore area was cementing (18 out of 54 blowouts reported). These well-control problems are normally caused by improper design of the cementing operation in terms of hydrostatic pressure of the cement slurries or preflushes, failure when mixing the cement slurry to achieve its planned density, lost circulation during the cement displacement, or failure of casing float equipment. In my opinion, well-control courses must dedicate more time to discussing well-control problems during cementing operations.
The second category encompasses those issues normally associated with the loss of hydrostatic pressure of the cement slurry during its initial hydration period and consequent gas flow inside the annulus. This condition also can cause well-control problems, pressure buildup in the annulus between casing strings, and zonal-isolation problems later on. The industry has several ways to mitigate these occurrences that include, but are not limited to, the use of gas-block additives, the design of cement slurries with short transition times, the application of surface pressure on the annulus, the use of external casing packers, and the implementation of multistage cementing operations. Despite the application of these mitigation measures, annular gas flow after cementing is still a recurrent problem, and remedial solutions are normally expensive and difficult.
The last category refers to long-term problems normally caused by poor cementing practices, with detrimental effects on zonal isolation. Inadequate drilling-mud removal during the cement-slurry displacement in the annulus, insufficient cement height that may lead to casing leakage and corrosion problems, and the channels that result from the gas flow previously mentioned are some of the factors that can contribute to long-term well-integrity failures. Again, remedial solutions are normally expensive.
Additional Reading
IPTC 16592 Mitigation of Deepwater Shallow Hazards With Simplified Cement System: South China Sea Case Study by Todd B. Ellis, Baker Hughes, et al.
OTC 24369 Well-Integrity Analysis Applied to Workover Prediction by T.C. da Fonseca, Petrobras, et al.
SPE/IADC 163474 Automated Alarms for Smart Flowback Fingerprinting and Early Kick Detection by Tarab H. Ali, Baker Hughes, et al.
