Objective To address the technical challenges in plugging oil-based drilling fluid losses in deep and ultra-deep wells, such as materials failure at high-temperature, poor compatibility with oil-based drilling fluids, and inadequate matching with multi-scale fractures, research and performance evaluation of high-temperature-resistant plugging materials have been carried out.

Method Based on the characteristics of leakage environment in deep and ultra-deep wells, a composite plugging material system with both high-temperature tolerance and oil-based compatibility was developed by evaluating the materials’ resistance to high-temperature aging in oil-based drilling fluids, their compatibility with such fluids, and their fracture-sealing capabilities.

Result The indoor test results showed that the developed plugging material system composited by flaky resin GPJ, organic particles and mineral particles GTK, and mineral fibre FHX had excellent resistance (maximum mass loss rate of 19.70%, maximum granularity degradation rate of 15.54%) to high-temperature aging at 200 ℃, 24 h, and had good compatibility with oil-based drilling fluids, the demulsification voltage drop rate was below to 10%, with a plugging pressure capacity of over 20 MPa for fractures ranging from 1 mm to 5 mm. The research results were applied on site in X-1 Well in the Xihu Sag of the East China Sea, the bearing capacity of the formation has been enhanced by 6.4 MPa (a drill fluid equvalent density of 0.17 g/cm³), and effectively resolved lost circulation issues with oil-based drilling fluid.

Conclusion The research achievement can effectively solve key technical challenges such as performance degradation, poor compatibility with oil-based drilling fluid, and insufficient coverage of multi-scale fractures at high-temperature environments of deep and ultra-deep wells. It provides valuable insights for treatment of drilling fluid leakage in deep formations and holds promising prospects for engineering applications.