Investigations on Casing-Cement Interaction with Application to Gas and CO2 Storage Wells

Abstract

Abstract This paper describes the construction and theoretical background of a new testing facility to investigate long-term sealability of cement recipes with application to storage gas wells. The first part deals with a theoretical downscaling of well conditions in order to determine the test parameters. Storage gas wells may have production casing strings with sizes up to 9 5/8" and therefore some downscaling criteria are necessary. The test facility representing an artificial annulus allows the simulation of the load changes and their effect on the cement. The adjustment of the test loads in the test facility is supported by an FEM-Analysis. This allows generating stresses in the test facility equal to those at the cement casing interface in the wellbore. The testing procedure is independent of the cement recipe and designed to expose the cement to common loads, as it has been found in gas or CO2 wells. Based on the visual observation, the measured axial and radial strains, axial displacement and test gas pressure drop it was possible to identify the development of a micro annulus and radial cracks in the cement sheath. The tests also showed that there is a region of minimum leakage in the failed cement sheath depending on the internal casing pressure.