Managing radioactive scale: Strategic approach and success story

Radioactive material contaminated, hard crystalline scale deposition on ESP & downhole equipment was resulting in frequent breaking of ESP shaft in a multilateral openhole producer. Extremely high workover cost in frequent replacement of downhole equipment and associated radioactive hazards, necessecitated a strategic MDT approach. Software usage and extensive laboratory backup helped finding the best possible option to mitigate this problem. Three possible well treatment options were investigated Scale inhibitor squeeze option was studied through reservoir condition core flow and rejected because of "probable formation impairment and placement difficulties in a complex well and reservoir geometry Periodic soaking of ESP with scale dissolver was considered a viable option because of economics and operational ease. Laboratory studies were conducted to design, the placement strategy. We developed a xanthan based high viscous self degrading polymer gel coushion which would support the scale inhibitor solution around the ESP for the necessary soaking period to prohibit flow into the pressure depleted formation. However this concept had to be abandoned because of flipping over of the fluids in laboratory observation and uncertainty of optimum soaking period downhole. The last and final option was to wait for the running ESP to fail and during workover the well could be completed with a macroni line for continuous injection of scale inhibitor. Judicial selection and optimization of inhibitor, continious monitoring of well treatment and well behavior has resulted in phenomenal success which is demonstrated by the fact that the ESP run life has been exceeded 700+ days against <100 days average runlife prior to treatment. The treatment also took care of radiation hazard and contaminated equipment disposal problem to a large extent.