Radial drilling technology with high-pressure water jet, which explores low-permeability andheavy oil reservoirs and the marginal, depleted oil wells effectively and economically, is appliedworldwide. Based on hydraulic principles, the pressure loss model of the radial drilling systemand the pulling force model of flexible hose connecting with the jet nozzle have been developed.The method to calculate the well extended limit is obtained. A sensitivity study is carried out toidentify the parameters controlling the well extended limit. The sensitivity study includes theeffect of flow rate, pump pressure, ratio between the flow rate of the forward and backwardorifices of the jet nozzle (flow rate ratio for short), well roughness, mother-well depth, and welldiameter. The result indicates that the method is reliable to calculate the well extended limit bycomparison with result of on-ground test. There exists an optimum flow rate of the forward andbackward orifices of the jet nozzle, which is 1.0 in value. The well extended limit is mostsensitive to pump pressure, flow rate, well roughness and flow rate ratio. The radial drillingtechnique is feasible to apply in deep wells. This study can provide theoretical guidance for themulti-orifices nozzle and radial drilling design in field operation.
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