The cement height requirements for primary cement jobs, or annulus cement, are stated as absolute values in some parts of the world. For example the Norsok Standard, D-010, "Well integrity in drilling and well operations" states that one cement barrier is either 50 meters when verified by displacement calculations, or 30 meters when verified by bonding logs. The requirements do not distinguish between reservoirs with high pressure/ temperature- and reservoirs with typical low pressure/termperature conditions. A numerical method has been developed which considers the current or future well conditions as part of the cement evaluation process. This numerical approach is an additional tool in the decision making process and does not replace existing verification practices. The time to run the analysis has also been an issue to address, since existing tools in the industry (FEM-analysis etc.) can be quite time consuming to run. Additionaly it is also possible to perform analysis up-front the operations and various pre-defined cement length intervals can be compared to the requirements or other upper acceptable cases. Offshore well cases from the Norwegian Continental Shelf have been used as basis in the development and demonstration of the method. The numerical model is based on monophase or multiphase Darcy flow calculations through the cement sheath involving uncertainties like cement permeability, reservoir pressure in the eternal perspective etc. The model allows a parametric analysis in a reasonable computation time and building of a well case library making the process efficient in an industrial comparison perspective. The method is an ‘engineering approach' taking place in the decision making process of well integrity.

You can access this article if you purchase or spend a download.