High-density water-or oil-based muds are not stable suspensions. Laboratory corrosion data and field observations suggest that solids-free, inhibited high-density brines could be ideal packer fluids for deep, hot wells. Expensive washover and fishing operations required for recovery of tubing stuck in settled mud solids could be eliminated. 2. Fluids must not deteriorate packer elastomers. 6 3. Fluids must remain pumpable during the life of the well; i.e., no high gelation or solidification may develop over time. 3,4 4. Fluids must not cause corrosion (inside casing or outside tubing).5. The fluids must not damage the producing formation because they may contact these producing zones during completion or workover operations. 3Water-based drilling-mud organic additives degrade upon prolonged exposure to high temperatures and sometimes generate corrosive gases, such as CO 2 and H 2 S. 3-5 Bacterial activity could also break down organic materials and/or produce corrosive elements.Lignosulfonate solutions can react electrochemically at metal surfaces to form sulfides, even at moderate temperatures. 3,4 Properly formulated oil-based muds are nonconductive and should not cause corrosion. 4 In case of packer failure or leaks, however, produced oil or gas dissolves in oil mud and destroys the suspension properties, allowing the weighting material (barite) to settle on top of the packer and to cause stuck packer and tubing.