Abstract

Recent increase in application of coiled tubing for horizontal wells and in particular underbalanced drilling triggered the necessity of a powerful downhole motor. More often downhole motor stalling and motor replacement is a problem when using with coiled tubing drilling system. To enhance the technology and make the system effective, optimization of drilling parameters is essentially required. The frequent motor replacement during the operation incrementally increases the operating cost despite deriving potential benefits from coiled tubing drilling. The key to improved coiled tubing drilling system is a unified system approach that encompasses motor and bit. This paper presents an analytical study on the optimization of motor performance and drilling parameters. A new simple test called wear-off test is defined to establish an operating window. The practical usefulness of the theory, backed by the fundamental and optimal analysis for roller cone and diamond bits, is demonstrated with numerical examples.

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