Influence of Casing Surface Roughness on Cement Plug Integrity

Evaluation of cement plug integrity is important for successful abandonment operations. Cement plug integrity is influenced by cement filling, but the effect of casing surface roughness on cement plug sealing has not been studied. Norwegian University of Science and Technology and Norwegian Industrial Institute of Science and Technology carried out research on the effect of casing inner surface on cement plugs, which was introduced in this paper. In the research, a cement ring integrity test equipment was applied to test pure cement plugs and silicate cement plugs in three steel pipes with different roughness of inner surfaces, i.e. smooth, medium roughness, high roughness, respectively. Computational fluid dynamics simulation was conducted under test conditions and the simulation results were compared with the test results. The results show that, both pure cement plug and silicate cement plug have poor sealing properties regardless of the inner surface roughness of steel pipe. When the pressure difference is less than 0.001 MPa, the gas leakage rate increases immediately. Rougher inner surface of steel pipes leads to lower gas leakage rate through cement plugs. Pure cement and silicate cement plugs act similarly in decreasing gas leakage rate by 80%～90% in rough steel pipes. The introduction in this paper is helpful to drive the development of abandonment technology in China.