Research On The Identification Technology Of First Cement Interface Micro-annulus

To evaluate cement quality accurately and ensure the cement bonding quality are important for production and subsequent operation of oil and gas wells. Micro-annulus don’t affect the hydraulic seal of production zone. As there is no shear coupling between the cement sheath and casing, micro-annulus will result in the rising of logging acoustic amplitude while evaluating the cementing quality. The characteristics of micro-annulus are similar to channeling in logging curve. They both cause the increasing of casing wave amplitude, which easily lead to the wrong judgment of cementing quality.Aimed at the first cementing interface micro-annulus, we sum up the main cause of the micro-annulus. According to the specific causes which are analyzed with mechanics, the size of micro-annulus can be predicted under different causes. Micro-annulus is studied through experimental simulation with vertical incident wave and casing slide wave. The various factors affecting the cement evaluation are studied by numerical simulation software. With this simulation model, the impact of different size of micro-annulus on sound wave propagation is studied. The numerical simulation results are accordance with experimental results. The micro-annulus experimental results show that the effects of micro-annulus on the vertical incident waves and casing slide wave propagation are both very significant. When micro-annulus size is 0.1mm, the first wave amplitude of vertical incident acoustic will reduce 70%. The increase of micro-annulus size will lead to the increase of the first received slide wave amplitude, and when micro-annulus size is higher than one number the well cementing will be misinterpreted as unqualified. However, the number is 0.05 mm in experiment and 0.02 mm in simulation.Finally, through the experimental and numerical simulation outcomes combining with micro-annulus size prediction model, the micro-annulus identification technology is established. With this identification technology, the logging results can be modified and the influence of micro-annulus can be eliminated. Then, we applied the identify technology to the field cement evaluation. It can be seen that the revised log curve is similar to the log curve with pressure logging and the cementing quality interpretation results are consistent. This proved that the micro-annulus identification technology can effectively eliminate the influence of micro-annulus on cement evaluation and ensure the correctness of cement evaluation.