Synthesis and Characterization of a Cationic Micro-crosslinking Polymer and its Application as a Fluid Loss Reducer in Water-based Drilling Fluids

Abstract

In addition to flat rheology to deal with the wellbore stabilization problem caused by narrow safety density window when drilling deepwater wells, upgrading the mud cake quality by fluid loss reducer and plugging to stabilize the wellbore is also an important measure to deal with this problem. For the existing fluid loss reducers for deepwater water-based drilling fluids, it is difficult to balance the plugging performance. In this study, a cationic micro-crosslinking polymer was synthesized as a fluid loss reducer by reversed-phase emulsion polymerization. N-isopropylacrylamide (NIPAM) and acrylamide (AM) were chosen as the main body of the synthesis to enhance the hydrophilicity of the products. Methacryloyloxyethyl trimethyl ammonium chloride (DMC) was selected to provide cationic groups to enhance the residency of the products in the formation. The molecular structure of ENAD was characterized using infrared spectroscopy (FT-IR), nuclear magnetic resonance hydrogen spectroscopy (NMR) and X-ray photoelectron spectroscopy (XPS), and the molecular structure of the product was as expected. The thermal stability of ENAD was analyzed by TGA, and the initial thermal decomposition temperature was 283 °C. The filtration effect of ENAD in BF under different media was evaluated. The experimental results show that ENAD can withstand temperature up to 150°C and has good filtration performance. 16h after aging at 150°C, the API filtration loss (FLAPI) is 8.8mL, the sand bed intrusion depth is 4.4cm, the high temperature and high pressure filtration loss (FLHTHP) is 32mL, the high temperature and high pressure filtration loss of plugging 10μm sand disc is 92mL. After comparing with sulfonated asphalt (FT), it is found that ENAD has better filtration performance. It is found that ENAD has better performance in reducing filtration loss. The mode of interaction between ENAD and the formation and its own mechanism of filtration loss reduction were analyzed by zeta potential analysis and SEM. With the increase of ENAD addition, the absolute values of zeta potential of BF before and after aging decreased from 48.7 and 32.1 to 43.3 and 27.1, respectively. ENAD enhances the interaction force with bentonite particles through its own adsorption properties. The strength of the mud cake is further strengthened by thermal deformation properties. It also enhances the force between the polymer and the formation through electrostatic gravitational adsorption, which further enhances the retention capacity of the polymer in the formation. Compared with conventional fluid loss reducers, ENAD has superior filtration effect and can be used as a fluid loss reducer for deepwater water-based drilling fluids.