The Technology of Setting Cement Plug for Offshore Ultra High Temperature and Ultra High Pressure Abandoned Wells

High density abandonment well plugs are set for ultra high temperature ultra high pressure exploratory wells drilled in Yingqiong Basin. Several problems, such as the conflict between mobility and sedimentation stability of the cement slurry, deterioration of the strength of the set cement, long section of cementing, big temperature difference, slow strength development at the top of cement, narrow safe drilling windows, loss of cement slurry and gas channeling etc., were encountered when setting the abandonment plugs. Several measures were taken to resolve these problems. First, spherical manganese ore powder was used to weight the cement slurry and to improve the rheology and sedimentation stability of the cement slurry. Second, a high temperature filming anti gas channeling agent was used to mitigate the risk of gas channeling. Third, an optimized amount of micro silica was used to increase the high temperature compressive strength of the set cement. Fourth, the quality of the spacer was optimized to enhance its ability to prevent loss of cement slurry. Finally, the cement slurry was squeezed into the hole to eliminate potential downhole problems. These measures have been successfully used in cement wells with maximum static bottom hole temperature of 213℃, and the highest density of cement slurry used was 2.50 g/cm³. Field operation showed that the cement slurry for setting abandonment plug has good mobility and sedimentation stability. The high temperature strength of the set cement developed fast and did not deteriorate. The cement slurry had stable thickening time, good anti-channeling and cement slurry loss preventing performance. All high pressure gas zones were successfully sealed off.