Transverse Hydraulic Fracture Initiation by Indentation in an Uncased Borehole

The hydraulic fracturing technique has applications in the development of solid mineral deposits. The particularities of the method performed in a mine condition include confined space and high requirements for the safety of the equipment used in underground workings. One of the most relevant tasks in in-mine hydraulic fracturing is creating parallel cracks oriented across the axis of the well. In-seam boreholes with this type of fracture system can be used for coal bed methane production, sealing of degassing boreholes, controlled collapse of the roof and other applications. In this paper we consider transverse crack formation on borehole wall in a given plane when the fracture initiation occurs due to an indenter impression located between two inflatable packers. During indentation fracturing, fluid under high pressure is supplied and this contributes to crack propagation in the desired direction. On the basis of the calculation of the stress intensity factor for the semi-infinite plane with the edge crack affected by the forces applied at points on the plane surface the length of the formed crack is obtained. The results show that the force acting on the wall of the borehole with a 76-105 mm diameter will be sufficient to create an initiation fracture in a predetermined direction. To implement this approach an experimental device is developed. It is implemented as an additional module of the hydraulic fracturing tool and equipped with a system of three indenters. The design of the device allows to obtain a total acting force in one plane and this will increase the effectiveness of the impact.