The Properties of an Environmentally Friendly High Temperature Salt Resistant Micrometer and Nanometer Filter Loss Reducer

Presently there are fewer environmentally friendly high temperature salt resistant filter loss reducers available in China, and the molecular structure of the filter loss reducers are also quite simple. In our studies, MND-1, a new environmentally friendly high temperature salt-resistant micrometer and nanometer filter loss reducer, was developed by the modification of hydroxyl ethyl cellulose (HEC), with 1-bromododecane as the initiator for the reaction. Graft copolymerization of HEC and nanometer CaCO₃ produced a product of macro molecules. Association among the macro molecules or among the different molecular chains of a single macro molecule produced supramolecular network structure of different morphologies. The interaction between the graft copolymer and the nanometer CaCO₃ helped stabilize the molecular structure of the final product and also enhanced the relevant properties of the final product. The filter loss reducer developed has small molecular volume and high specific area. The molecules of MND-1 can form a spatial network structure through hydrogen bonds and Van der Waal’s force among the hydroxyl groups in the molecules. The strength of this spatial network is not strong enough to resist high shear rates, and the viscosity of the MND-1 solution is thus decreased at high shear rates. When shearing stops, MND-1 regains its spatial network structure formed through the association forces among the molecules of MND-1, and the MND-1 solution resumes its viscosity. This is the so-called shear thinning effect formed through a dynamic equilibrium between the destruction and recovery of the spatial network structure. With this excellent shear thinning effect, MND-1 can effectively seal the voids in mud cakes, thereby reducing the rate of filtration. Laboratory evaluation experiment showed that MND-1 has excellent filtration control capacity in freshwater, saltwater and saturated saltwater drilling fluids. The API filter loss of an MND-1 treated saturated saltwater base drilling fluid aged at 180 ℃ for 16 h was only 6.8 mL. MND-1 is environmentally friendly and easy to biodegrade, it has an EC₅₀ of 4.3×10⁴ mg/L.MND-1 can be used in drilling high temperature salt formations in environmentally sensitive areas.