Multilateral-horizontal-well drilling is an efficient approach for stimulating shallow, low-permeability, marginal, and coalbedmethane (CBM) reservoirs. Radial-jet-drilling (RJD) technology, which uses a high-pressure water jet, aims to drill tens of laterals from a vertical wellbore. Hydraulics design is essential for successful field-drilling operations. However, detailed hydraulics calculations and design methods have not yet been published. In this study, the pressure loss, ejector force, and extending resistance of an RJD system were measured at different flow rates at a full-scale RJD experimental facility. A set of pressure-loss models and a lateral-extending-force model of an RJD system were then established, and a method to optimize the hydraulics of RJD was proposed. Finally, a field case study with six radial laterals in four different layers was conducted by use of our models and optimization method. The hydraulics calculations corresponded well with the field data. The model error was within 8%. The pressure loss of the high-pressure hose and jet bit represents a large proportion of the RJD-system pressure loss (41.2 and 55.8%, respectively). According to the operation profile, the calculated pump pressure will help the field engineer to estimate the working status of downhole tools. The results show that the pump flow rate should be optimized for different well configurations. The optimum flow-rate range was determined by the minimum lateral-extending force, minimum rock-breaking jet-bit-pressure drop, and minimum equipment-safety working pressure. To maximize the rate of penetration (ROP), the largest flow rate within that interval was selected as the optimum flow rate. A flow rate of 57.24 L/min was optimal for the case well. The present work provides a viable and detailed hydraulics-calculation model and design method for RJD, and may be used for both short-term troubleshooting and long-term operation planning. It can serve as a guide for the development of safer and more-effective RJD practices.
