ABSTRACT:

Radial drilling-fracturing, the integration of radial drilling and hydraulic fracturing, is an innovative approach to develop coalbed methane (CBM). The objective of this article is to investigate fracture initiation and propagation characteristics for different radial borehole parameters. We conducted experiments using a true tri-axial fracturing simulation system under different lateral lengths, counts and azimuths. High-rank coals from the outcrop were used as the raw samples for the experiments. Results show that: the best effect is achieved when it initiates from the bedding plane where the laterals lie and forms a fracture network with one main horizontal fracture connecting multiple vertical fractures; the breakdown and injection pressure decrease with the lateral length and count increasing; increasing the lateral length enlarges the horizontal fracture area; and the optimal lateral design for horizontal initiation is four laterals with the phase of 90° and each lateral is at 45° from the horizontal in-situ stress. The key findings of this work could provide critical insights into understanding radial drilling-fracturing characteristics.

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