Laboratory Research on the Mechanism of Organic Salts Improving the High-Temperature Performance of High-Density Drilling Fluids

Summary Organic salt-based drilling fluids are recognized for their superior shale inhibition, wellbore stability, environmental compatibility, and thermal resistance. However, the mechanism by which organic salts enhance the high-temperature performance of drilling fluids and their influence on fluid properties under extreme conditions is not well understood. Investigating the role of organic salts in improving the thermal resistance of additives and drilling fluid systems is crucial for advancing thermal stability and facilitating drilling operations in deeper, high-temperature formations. In this study, the effects of organic salts on water-based drilling fluid additives and low-solids organic salt drilling fluid systems were systematically examined before and after thermal aging through rheological, filtration, and sedimentation stability tests. The microstructural characteristics were further analyzed using zeta potential measurements, particle-size distribution (PSD), and scanning electron microscopy (SEM). The results indicate that the addition of organic salts increases the absolute value of zeta potential, enhances particle size uniformity, reduces size fluctuation, and significantly improves the dispersion stability of colloidal particles, leading to denser filter cakes. At a concentration of only 5.0 wt% organic salt, the rheological properties were notably improved, and the fluid-loss control performance of filtrate reducers was enhanced. At higher concentrations (40.0 wt%), corresponding to a fluid density of 2.0 g/cm³, the system maintained stable rheological, filtration, and sedimentation properties before and after aging at 230°C. These findings demonstrate that organic salts significantly enhance the thermal stability of both drilling fluid additives and systems. Based on these results, a high-temperature-resistant, high-density organic saltwater-based drilling fluid system was formulated and successfully applied in the Gaitan-X well. Field results confirmed its excellent thermal stability and operational reliability, effectively addressing challenges of hole cleaning, lost circulation, and wellbore stability in high-temperature deep formations.