Development and application of an electromagnetic relay transmission MWD system

Effective monitoring and well deviation control are of great significance to the deviation control and fast drilling in gas drilling as well as to the directional and horizontal well drilling. However, the present EM-MWD system is restricted in application and promotion as its transmission depth is greatly influenced by the formation resistivity, especially the fast signal attenuation in low resistivity formation. Consequently, the key issue is how to improve the transmission depth. Therefore, the modular EM-MWD relay transmission scheme, which means "measurement assembly + relay cable + transmitter assembly", was first proposed in China, followed by the development of a set of electromagnetic relay transmission measurement while-drilling system (Model CQEMWD-I). The transmitter assembly, located in the central of drill string, receives the measurement data transmitted from measurement assembly via relay cable and sends electromagnetic wave signals to the ground. In this way, the electromagnetic relay transmission is achieved to extend the measurement depth. Through the application of the CQEMWD-I system in 6 wells in gas drilling and 4 wells in mud drilling, the telemetering vertical depth reached up to 3841 m and the effective measurement data were acquired. The successful development and pilot tests of this system signifies a breakthrough of the trajectory measurement technology in gas drilling of directional and horizontal wells; moreover, the system fills up the domestic gap in gas drilling and MWD technologies and ranks among the advanced similar foreign technologies.