The ultrashort radius lateral drilling technique has applied more than 20 wells in China, and it was reported that this technique increased the production of mature oil wells by 3 to 5 times in average. However, when the casing grade was relatively high, the flexible drilling tool was cut off by the sharp edge of open window. This paper will introduce a method to improve this technique.

By studying the failure case, there were two obvious defects for this drilling tool. First, the shell material was too soft. It was radially stripped of 2 to 3 mm. Second, the design of transmission fork was unreasonable. The cylindrical pins of transmission fork were placed from the outside of shell and were covered by welded discs. When the shell was stripped, pin was easy to drop off and causes disconnection. To find the essential cause, we deduce kinematics and dynamics analyzes, and redesign the structure of transmission fork. Test shows the performance of new tool is much better.

This paper introduces kinematics and dynamic to redesign the ultrashort radius lateral drilling tool, which improves the performance by principle. Though kinematics analyze, we found the rotational speed inhomogeneity might cause inefficient drilling depth, even sticking of tool in some extreme cases. Tough dynamic analyze, we found the additional torque caused by rotational speed inhomogeneity might cause the vibration of drilling tool, which may cause more serious problem. To solve these problems, the universal joint was design into constant velocity universal joint and the mounting position of transmission part was placed from inside to give enough margin for shell stripping off. After these work, the ultrashort radius lateral drilling tool has less vibration and provides continuous and stable torque. This method improves the efficiency and success rate of this technique.

This paper updates the design method of ultrashort radius lateral drilling technique, makes it much reliable and efficient. It will give the promise for the next generation technique, the ultrashort radius lateral coring technique.

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