Microhole Drilling Tractor Technology Development

Abstract

In an effort to increase the U.S. energy reserves and lower costs for finding and retrieving oil, the USDOE created a solicitation to encourage industry to focus on means to operate in small diameter well-Microhole. Partially in response to this solicitation and because Western Well Tool's (WWT) corporate objective to develop small diameter coiled tubing drilling tractor, WWT responded to and was awarded a contract to design, prototype, shop test, and field demonstrate a Microhole Drilling Tractor (MDT). The benefit to the oil industry and the US consumer from the project is that with the MDT's ability to facilitate Coiled Tubing drilled wells to be 1000-3000 feet longer horizontally, US brown fields can be more efficiently exploited resulting in fewer wells, less environmental impact, greater and faster oil recovery, and lower drilling costs. Shortly after award of the contract, WWT was approached by a major oil company that strongly indicated that the specified size of a tractor of 3.0 inches diameter was inappropriate and that immediate applications for a 3.38-inch diameter tractor would substantially increase the usefulness of the tool to the oil industry. Based on this along with an understanding with the oil company to use the tractor in multiple field applications, WWT applied for and was granted a no-cost change-of-scope contract amendment to design, manufacture, assemble, shop test and field demonstrate a prototype a 3.38 inch diameter MDT. Utilizing existing WWT tractor technology and conforming to an industry developed specification for the tool, the Microhole Drilling Tractor was designed. Specific features of the MDT that increase it usefulness are: (1) Operation on differential pressure of the drilling fluid, (2) On-Off Capability, (3) Patented unique gripping elements (4) High strength and flexibility, (5) Compatibility to existing Coiled Tubing drilling equipment and operations. The ability to power the MDT with drilling fluid results in a highly efficient tool that both delivers high level of force for the pressure available and inherently increases downhole reliability because parts are less subject to contamination. The On-Off feature is essential to drilling to allow the Driller to turn off the tractor and pull back while circulating in cleanout runs that keep the hole clean of drilling debris. The gripping elements have wide contact surfaces to the formation to allow high loads without damage to the formation. As part of the development materials evaluations were conducted to verify compatibility with anticipated drilling and well bore fluids. Experiments demonstrated that the materials of the tractor are essentially undamaged by exposure to typical drilling fluids used for horizontal coiled tubing drilling. The design for the MDT was completed, qualified vendors identified, parts procured, received, inspected, and a prototype was assembled. As part of the assembly process, WWT prepared Manufacturing instructions (MI) that detail the assembly process and identify quality assurance inspection points. Subsequent to assembly, functional tests were performed. Functional tests consisted of placing the MDT on jack stands, connecting a high pressure source to the tractor, and verifying On-Off functions, walking motion, and operation over a range of pressures. Next, the Shop Demonstration Test was performed. An existing WWT test fixture was modified to accommodate operation of the 3.38 inch diameter MDT. The fixture simulated the tension applied to a tractor while walking (pulling) inside 4.0 inch diameter pipe. The MDT demonstrated: (1) On-off function, (2) Pulling forces proportional to available differential pressure up to 4000 lbs, (3) Walking speeds to 1100 ft/hour. A field Demonstration of the MDT was arranged with a major oil company operating in Alaska. A demonstration well with a Measured Depth of approximately 15,000 ft was selected; however because of problems with the well drilling was stopped before the planned MDT usage. Alternatively, functional and operational tests were run with the MDT inside 4.5 inch tubing at depths of 800-950 ft. The MDT successfully demonstrated On-Off capability, pulled with up to 1465 lbs force, and verified its capability to transmit torque though it from the Orienter. Forces generated by the tractor were limited due to insufficient differential pressure because of the unloaded downhole motor, which is not typical during drilling conditions. Additionally, the Coefficient of Friction between the MDT grippers and the tubing was much less than the anticipated COF of the sandstone formation. Despite these minor limitations, to summarize the MDT operated as expected. Minor modifications to the MDT are being incorporated to improve gripping capability of the tractor. Additional demonstration wells are being arranged to expand on the project's goals of delivering a fully operational utilitarian tool for use throughout the US to improve reserves.