Synthesis and Application of Polyether Fatty Acid Rheology Modifier for Oil-based Drilling Fluids

Oil-based drilling fluids have low gel strengths and pipe sticking by the settled drilled cuttings is easy to be encountered. A polyether fatty acid gelling agent LQZ has been developed to deal with this problem. The molecular structure, thermal stability, gelling property and emulsion stability of the synthesized LQZ were analyzed using IR spectroscopy, thermogravimetric curve, gel strength measurement and emulsion stability test. The effects of the base oil for formulating the mud, oil/water ratio, density and temperature on the gelling performance of the LQZ were investigated. It was found that in the LQZ molecules there are polar groups such as hydroxyl, amide and ether bond which can form network structures. The network structures render the LQZ a fast weak gelling characteristics. At 300 ℃, the LQZ has no obvious thermal decomposition. The LQZ is beneficial to the emulsion stability of the oil-based muds at a concentration of less than 0.85%. The LQZ can be used in various nonaqueous drilling fluids formulated with white oil, diesel oil or synthetic fluids, with white oil-based drilling fluids being the best environment for the LQZ. LQZ in an oil-based mud with oil/water ratio of 8∶2 and density of 2.1 g/cm³ has the optimum gelling capacity at 190 ℃, the yield point, the low shear rate, φ₆ and φ₃ reading and the gel strengths are all doubled. Compared with the similar products produced abroad, LQZ has the advantages of increasing gel strengths of a mud, without simultaneously increasing the plastic viscosity of the mud. In field operation, 1% LQZ in a white oil-based drilling fluid and in a diesel oil-based drilling fluid increased the gel strengths of the muds by more than twice, and the plastic viscosity was only slightly increased. The LQZ can be used to improve the suspending capacity of an oil-based drilling fluid.