Abstract
Over the ages of the well drilling history, primary and remedial cementing remains one of the most challenging activities with direct effect on the well life and well integrity status. This paper is based on the actual lessons learned and latest best practices in zonal isolation of Company fields developed according to business requirements during drilling and workover operations. It covers the aspects of primary cementing in two main types of casing design, and describes major challenges associated. Authors tried to define a clear criteria on what can be considered as the minimum acceptable zonal isolation, what are the issues associated with its evaluation, what needs to be done in order to meet those criteria. Additionally, there is an analysis done on the direct impact of the cementing job on the well life. Particularly, the focus is made on well integrity related issues and remedial solutions to cure them based on successful case histories. The paper answers on many questions related to the consequences of the poor cement isolation (up to well control incidents), as an actual lessons learned collected over the 60 years of operation.
The impact of the casing design on the well integrity status is analyzed based on the results of wellhead pressure monitoring of around 4,000 wells. It includes revision and analysis of cement evaluation logs of wells with behind casing communication (sustained pressure in "B" annulus) along with the challenges associated with the diagnostic investigations of the leak source. Various cementing remedial techniques are described with pros and cons analysis and actual case histories including results of post-job wellhead pressure monitoring. The subject of swelling phenomena of soft shale formations and its effect on acoustic based tools for cement bond evaluation is touched as well. Finally, the paper contains interesting results of the recent corrosion logging campaign that reveals a correlation between casing condition and casing design.
