Study and Application of Solids-free Flushing Spacer

A solids-free flushing spacer was developed for use in drilling operation to prevent open holes and high permeability sandstones from being damaged by the solids in spacers. In laboratory experiments, the density of the spacer can be adjusted between 1.00 g/cm³ and 1.80 g/cm³. No density difference was found of the top and the bottom of the spacer after aging at 180℃, indicating that no sedimentation ever occurred. The spacer was a Newtonian fluid, having plastic viscosity of 6 mPa·s and yield value of 0, meaning that turbulent flow displacement can be easily realized. When contaminated with a mixture of organic salt drilling fluid and salt-resistant cement slurry, the flow index of the spacer increased, while the consistency factor decreased, meaning that the spacer was compatible with organic salt drilling fluid and salt-resistant cement slurry. When mixed with saltwater at different ratios, thickening time of the mixture was prolonged, which is beneficial to safe operations. 90% or more pseudo mud cakes and oil dirt on the borehole wall can be flushed away, which is beneficial to the development of bonding strength between cement sheath and borehole wall. This solids-free spacer has been used 29 times in Iraq, successfully solving problems encountered in cementing high temperature wells, and wells with salt and gypsum formations.