Study and Application of Scale Inhibitive Solids-free Workover Fluid

Calcium chloride workover fluid was modified through optimization of additives used in the workover fluid, such as scale inhibitor, corrosion inhibitive cleanup additive, swelling inhibitor and weighting agent, in an effort to solve the problem of scaling caused by calcium chloride workover fluid and sodium bicarbonate formation water. As a result of the modification, a calcium chloride solids-free workover fluid of 1.20-1.55 g/cm³ was developed. By treatment with BH-1, a scale inhibitor, the workover fluid is compatible with sodium bicarbonate formation water. It is highly efficient in clay inhibition, and has rates of corrosion to tubing steel that are equivalent to fresh water. This workover fluid has surface tension that is less than 43.8% that of fresh water, and freezing point between -10℃--55℃. It is compatible with crude oil, and is suitable for use in wells having sodium sulphate water, sodium bicarbonate water, calcium chloride water and magnesium chloride water. This workover fluid had been successfully applied in four wells.