213 upward drilling pilot hole method is more difficult to control due to the drill bit being under pressure. Figure 3 - Schematic diagram of a reverse drilling rig drilling pilot hole from bottom to top. Figure 4 - Schematic diagram of a dedicated directional drilling rig drilling pilot hole. For deep wells, deviated wells, and wellbore projects with high deviation requirements, including single-drilling well completion projects using raise boring machines (RBMs), precise control of deviation is necessary to ensure the effective cross-section and functionality of the wellbore. Using a dedicated directional drilling rig and related instruments (Figure 4), technologies such as MWD (Measuring While Drilling), screw drill string deviation correction, and mud pulse signal transmission are implemented to ensure the pilot hole follows a predetermined trajectory. However, the power for deviation correction using the screw downhole motor is generated by the mud pump, requiring a high-power mud pump and resulting in high energy consumption. 2.2 Pilot Well Drilling Technology A conventional raise boring machine is used. The drill pipe extends into the lower horizontal roadway, the pilot hole bit is removed, and a reaming bit is connected. Drilling proceeds from bottom to top. Upon reaching the upper horizontal level or surface, the raise boring machine is removed, the reaming bit is retrieved, and the pilot well construction is complete. For raise boring machines, two reaming methods can be used: The first is the topguide-bottom-reaming method, where the pilot hole bit is removed in the upper horizontal roadway, and after connecting the reaming bit, drilling proceeds from top to bottom (Figure 5). In this method, the annular space between the pilot hole and the drill pipe is relatively small, increasing drilling friction resistance and drill pipe wear. The diameter of the reaming in one stage is limited, and generally a two-stage reaming method is used, with the second stage reaching the required pilot hole diameter. The second reaming method is bottom-up reaming (Figure 6), where guides and stabilizers are installed in the drilled pilot hole and the formed reamed hole to prevent drill pipe instability and fatigue damage.
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