Extended Horizontal Jet Drilling for EGS Applications in Petrothermal Environments
S. HAHN, V. WITTIG, R. BRACKE
[International Geothermal Centre Bochum, Germany]
High pressure water jet drilling technologies are widely used in the drilling industry. Especially in geothermal and hard rock applications, horizontal (radial) jet drilling is, however, confronted with several limitations like lateral length, hole size and steerability. In order to serve as a serious alternative to conventional stimulation techniques these high pressure jetting techniques are experimentally investigated to gain fundamental knowledge about the fluid-structure interaction, to enhance the rock failing process and to identify the governing drilling parameters. The experimental program carried out at GZB is divided into three levels. In a first step jetting experiments are performed under free surface conditions, while logging fluid pressures, flow speeds and extracted rock volume. All process parameters are quantified with a self-developed jet-ability index and compared to the rock properties. In a second step experiments will be performed under pressure-controlled conditions. Therefore a test bench is used that enables to set rock cores of up to 40cm of length 15cm of diameter under pressure until 200bar while jetting with equipment and conditions of field standard. The experimental results from levels 1 and 2 allow to identify the governing rock failure mechanisms and to correlate them with physical rock properties and limited reservoir conditions. Results of the initial tests do show a clear dependency of achievable penetration depth on the interaction of jetting and rock parameters and an individual threshold of the nozzle outlet velocity can be noticed in order to successfully penetrate different formation types. At level 3 jetting experiments will be performed at simulated reservoir conditions corresponding to 5.000 m depth (e.g. up to 1.250 bar and 180 °C) on large samples with a diameter of 25 cm and a length of up to 3m using GZB´s in-situ borehole and geofluid simulator ‘iBOGS’. Experiments will be documented by active and passive ultrasound measurements and high speed imaging. Acknowledgement Jetting research and work at GZB has received funding in part from the European Union’s Horizon 2020 research and innovation program under grant agreement No 654662 and also from federal government GER and state of NRW.
|        Topic: Drilling and Completion Technology||Paper Number: 21074|