Design of a Testing Cell for Cement Sheath Integrity
Research output: Research › Master's Thesis
In order to produce hydrocarbons in an economic and environmentally friendly way, zonal isolation of the wellbore is very important. The isolation of wellbore fluids from the surrounding formation is achieved through effective cement placement. Cement is a brittle material which can fail when subjected to repeated application of stresses lesser in magnitude than the statically determined strength. In the field of mechanics of materials, repeated application of stress is referred to as fatigue loading. Well events such as workover, well testing or hydraulic fracturing apply fatigue loads to the wellbore system. To ensure safe and reliable production it is important to understand the impact of fatigue on the cement sheath. First, this thesis investigates bonding mechanism between casing and cement. Second, it covers factors that influence the durability of the bond. Factors caused either through the composition of the cement, the cementing process or environmental induced changes over time. Furthermore, it also covers cement integrity issues from cement shrinkage, gas migration and well development. The cement failure at the interfacial transition zone is described in detail and an additional section describes the effect of fatigue on cement mechanical properties. Finally, this thesis designs a test cell for fatigue testing of the cement-steel bond and also lists considerations during that process. The set-up includes casing and cement, allowing the whole system to be tested in one assembly at laboratory scale. The testing specimens are composed of a steel pipe cemented and a cover or cell outside. A weight comparison of all test cell components is made for steel and aluminum. Relevant measurements after curing are addressed and a complete testing procedure is included which covers test build-up, actual testing, dismounting and clean-up.