Low-Cost, High-Strength, Insulating Sub Manufacturing Method
Publication Date: 2005-Sep-23
The IP.com Prior Art Database
Introduction: For EM (Electromagnetic) telemetry to effectively work, it is imperative that an insulating sub be placed in the string to keep the signal from shorting out on to the workstring. It has been difficult to achieve a strong, low cost insulating sub (gap sub). Problem with Prior Art – Current Technology: Previous gap subs have used a variety of methods to achieve the electrical isolation. One has been the use of an insulating ceramic spray coating on one half of a drill pipe threaded connection. This has the disadvantage of being expensive and very fragile. Also if the coating becomes nicked or otherwise damaged, the part must be sent out again to the coating vendor. Another method has been to use a composite (fiberglass) section with metal crossovers. This design has very low strength so it can only be used in very low stress installations such as hanging below a packer. Yet another has been to use anodized aluminum parts which can suffer from excessive corrosion as well as being low strength. Objective: The intent of this new design is to allow for a low cost, quickly repairable insulating gap sub. Potential Applications: This gap sub could be used for both EM Telemetry as well as electrical isolation for corrosion resistance. For material cost savings, customer sometimes use corrosion resistant materials for part of the tools and string but then use less corrosion resistant materials for the tubulars to the surface. This drives an accelerated corrosion to the less resistant materials by a galvanic reaction. This reaction requires a path for electrons to move between the different materials. By the use of an insulating gap sub, the electrical path is stopped which effectively halts the galvanic reaction and subsequent accelerated corrosion. New Approach: (See attached sketch) This invention involves a method to achieve a low cost high strength gap sub that is easily repairable. For example it can be made with the following steps. The box thread is cut with a 6 sub acme thread cutter but at a 3 threads per inch rate. This leaves an unusually large area between each thread. The pin thread is cut as a standard 3 sub scme thread. The threaded area on the pin is then filled completely with an epoxy such as "Weld A" with a coating also on the od of the thread. Once cured, a 6 stub acme cutter is used at 3 threads per inch centered in the previously cut 3 stub acme thread. This makes for an epoxy thread that is supported by the metal. For final installation, additional "Weld A" is used as the thread is permanently made up. One or more optional peek shoulder rings can be bused if high loads are expected when making up the thread. This helps reduce the load on the epoxy and seal off the epoxy from the environment. Of course changes to this method could be made such as difference sizes of threads or even different types of threads such as a v-thread. In a second embodiment of this invention, a peek (or other similar insulating material) part could be used to provide the insulation instead of the epoxy. The peek could be wrapped or injection molded onto the pin thread or the peek could be a separate part that is threaded onto the pin. Advantages of New Approach: This design allows for a method of making an insulating gap sub that is completely in-house. It therefore can be made faster and less expensive than a connection that must be sent outside for processing.