Coating Optimized for Abrasion and Fatigue Resistance for Use in Extreme Well Geometries

Abstract

Abstract Extreme well geometries, extended reach wells, and other applications that test the technological limitations of drill strings and tools are becoming more commonplace in the industry. A new high velocity oxy fuel (HVOF) applied tungsten carbide coating has been developed for use on performance drilling tools for these challenging applications. Tungsten carbide coatings are known for abrasion resistance and lab testing has proven this coating is also ductile. Key benefits include reducing the risk of damage or failure of critical drilling tools and pushing the technology envelope. Extensive testing shows excellent resistance to repeated bending cycles, which leads to cracking and possibly catastrophic failures in drilling environments. In order to develop a suitable coating for fatigue resistance, abrasion resistance and cost, several hard-facing coatings and application methods that have been continuously developed for downhole tool applications were selected for extensive lab testing. The coating hardness and the ductility of the matrix within which the tungsten carbide resides were optimized, inducing more abrasion resistance and raising the fatigue life. Rotating drilling tools now have a coating that has been identified and tested as acceptable for use in extreme well geometries. Directional assemblies, jars, torque and drag reduction subs, and any other rotating tools susceptible to wear that are used in high dogleg environments are all potential beneficiaries of a highly reliable coating. A test with a standard tungsten carbide HVOF hard-facing coating and application method generated cracks within the coating. These cracks did not propagate into the base metal, but it is conventionally impossible for inspectors to differentiate between cracks in the coating vs. the base metal. The decision was made to explore different methods with regard to the coating thickness, matrix ductility, application method. Multiple coatings tested on varying sizes of tools has led to the development of a tungsten carbide coating that has withstood 10,000,000 cycles at 12 deg/100 ft, and an additional 2,000,000 cycles at 25 deg/100 ft, without the development of fatigue cracks. The test was concluded when the mounting apparatus gave out. The coating will assist in pushing the technical envelope that restricts operators from economically reaching reservoirs in today's challenging energy environment. Main contributions are an expansion of the technology envelope and the reduction of risk related to damaged tools and failures while drilling challenging wells.