A Generalized Hydraulic Model for Propulsion Force Calculations in Radial Jet Drilling


 Radial jet drilling (RJD) involves drilling several small-diameter lateral holes from a single vertical wellbore to increase reservoir contact and production. RJD system components (diverter, flexible hose, and jetting bit) are conveyed to the target depth using coiled tubing. A high-pressure flexible hose is used in conjunction with a jetting bit to drill holes laterally. Without a rigid drillstring, no axial force can be transferred to the bit as it penetrates the rock. As a result, the bit is propelled by hydraulic means. Thus, in addition to front-jetting nozzles, RJD bits use back-jetting nozzles. Therefore, the rate of penetration (ROP) and maximum hole length (MHL) must be maximized through proper hydraulic optimization. Existing hydraulic models rely on field-measured parameters (discharge coefficient and flow rate ratio) that vary by the bit design to predict the propulsion force, bit hydraulic power, and the maximum lateral hole length. Hence, this study aims to develop a generalized and accurate hydraulic model that does not require field-measured parameters to make predictions. As a result, the new model can be used for optimizing RJD operations by selecting suitable bit designs and lateral hole geometries.
 This article presents a new RJD hydraulic model that uses a discharge coefficient that varies with the nozzle aspect ratio. The model predicts the propulsion force, differential pressure across the bit, and MHL based on the design of the bit, nozzle, and lateral hole geometries, and flow rate. To verify the model, extensive experiments were conducted with single-nozzle and multi-nozzle jetting bits. The pump pressure was varied while flow rate and propulsion force were recorded during the tests. Model predictions are compared and validated with experimental data. Measured and model-predicted propulsion forces demonstrate a reasonable agreement with a maximum discrepancy of 25%. Once the model has been validated, it is used to perform a parametric study to investigate the influence of various factors on bit performance. According to the parametric study, nozzle and hole diameters, friction factor, and hose density strongly influence bit performance. Furthermore, the diameter of the nozzle has been found to have a significant effect on bit performance parameters (propulsion force, bit hydraulic power, and MHL).