Enhancing of spacer fluids compositions for well cementing

Abstract

Currently, almost all researchers believe that turbulent flow is the most preferred displacement mode. However, when it comes to cementing, where practical limitations prevent obtaining turbulent flow, opinions begin to differ. In general, either «very slow» flow or «very fast» flow is recommended for all wells in the annulus. There are mainly two types of buffer liquids used – «wash» and «space». The first buffer liquid is «wash», which washes away and removes the remnants of drilling fluid, clay cake, etc., and the second is «space», a thicker system, entering the cavities, cleans them and also pulls out all the remnants of the first buffer liquid to the surface. The first buffer fluid is «wash», basically a thinner, of the drilling fluid, which may contain surfactants - surfactants or liquid-restraining agents, the preferred mode of motion is turbulent. The second buffer liquid – «space», can mainly contain polymeric materials, weighting agents, the preferred mode of movement is laminar (cork). The choice of these fluids is determined by their chemical compatibility with drilling and cement slurries, their effectiveness in removing the drilling fluid. Very important postulates adopted by almost all leading oil firms are given. A new and very affordable composition of the buffer liquid of the following composition has been proposed: «wash» - FLS - 4%, diesel fuel - 2%, the rest is water - 9%; «space» - carboxymethylcellulose (CMC) - 0.5%, bentonite solution with a density of 1030 kg/m3 - 99.5%. If necessary, these buffer fluids can be weighted, for example, with barite, to an average density between the densities of drilling and cement slurries in a given well.. Keywords: buffer fluid; drilling fluid; cement mortar;turbulent flow; mode of motion; mud cake; centralizer; casing string.