Abstract: In order to effectively develop the Sadi ultra-low permeability reservoir, the optimal method for arranging fishbone well schemes was studied in accordance with the characteristics of reservoir and the conditions of fishbone well drilling, by comprehensively considering the reservoir geology and engineering factors. as the goal was to obtain the optimal fishbone well arrangement scheme that can satisfy the need for both development and smooth drilling under extreme drilling conditions. First, the ultimate drilling depths of the main wellbore and branch hole of the fishbone well were determined based on the geological conditions of the Sadi reservoir and the drilling capacity of conventional directional wells. Then, by taking the cumulative oil production as the preferred target, the influences of main parameters (such as the number of branch hole, the length of branch wellbore, the spacing between adjacent branch holes, the included angle between the branch hole and main wellbore, and different fishbone wellbore deployment schemes) on the cumulative oil production were analyzed to determine the wellbore deployment scheme with higher cumulative oil production. Next, according to the drilling difficulty of different trajectories of the fishbone well, a corresponding model was established to evaluate the drilling risks of different wellbore deployment schemes and determine the scheme with lower drilling cost. Finally, the wellbore arrangement schemes for 4 branch hole length of 730.00 m and 3 branch hole length of 800.00 m were selected as the best schemes for the fishbone well of the Sadi reservoir. The application of the optimal wellbore arrangement scheme has provided high cumulative oil production, with controllable drilling risk and lower drilling cost. The proposed optimal method of fishbone well arrangement schemes combined closely the drilling engineering and the reservoir engineering geology, so as to provide the reservoir engineer an idea of selecting a fishbone well arrangement scheme, and to give a reference for design of fishbone wellbore for similar oilfields.