Abstract

In CBM drilling, high-efficient, low-cost MWD and geosteering tools are needed to ensure the cost-efficiency of large-scale gas development. Especially in a cluster and horizontal coalbed methane well drilling environment, one of the most effective methods to enhance the individual well producing rate is to keep the bit always in the best position to extend along the target layer.

The DREMWD CBM drilling geosteering system adopts electromagnetic information transmission technology. Compared to traditional mud pulse technology, it has such advantages as a wide range of media applications, deep non-relay transmission, a fast signal transmission rate, and a low failure rate of field applications. Moreover, it can measure wellbore trajectory and geological parameters, so as to ensure actual wellbores to penetrate into coal seams and get the best position. Therefore, it has quickly become a leading geosteering tool for CBM drilling.

The DREMWD system consists of downhole tools and surface units. Downhole tools are mainly composed of the high-power generator, orientation sensor, natural gamma sensor, electromagnetic transmitter circuit, insulation transmitting antenna, and non-magnetic drill collar. Surface units are mainly composed of the signal receiver, ground antenna, driller display, and signal processing and analysis software. With its unique high-power downhole generation technology, greatly enhancing emission intensity and formation penetration. The rotary dynamic azimuth natural gamma measurement module is composed of a natural gamma sensor, a rolling angle sensor and a signal processing circuit. It can perform real-time measurement of the formation natural gamma within a certain fan-shaped range at upper and lower levels. The system has been widely used in the CBM drilling in Qinshui basin in China with good effect.

With this geosteering tool, the drilling performance and recovery efficiency have been remarkably improved. This paper will highlight the technical development and present helpful case histories and recommendations.

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