Laboratory Study on the Application of Reciprocating Multi-stage Reaming Drilling for Horizontal Wells in Tectonically Deformed Coal Seams

The formation of boreholes in tectonically deformed coal (TDC) seams is challenging, hindering the efficient exploitation of coalbed methane (CBM) resources. The reciprocating multi-stage reaming drilling technology presents a promising solution for realizing the formation of horizontal wells in TDC seams that are broken, high-pressure, and collapse-prone. To investigate it, an engineering-geological model was established to conduct physical simulation tests of multi-stage reaming drilling in horizontal wells of the TDC seams using the 11–2 TDC seam of Zhangji Mine in the Huainan Mining District as the geological prototype. Reformed tectonic coal was used to simulate the natural stratum, and drilling parameters were recorded. The test obtained a 110 mm borehole to simulate the reality of 550 mm, and the final hole was 284% of the initial one, which achieved the target and completed the design requirements. During the process, the drilling thrust force and drilling speed remained stable, while the torque increased progressively, and the unsupported borehole wall remained intact after completion. The laboratory results demonstrate that the reciprocating multi-stage reaming drilling technology can be applied in TDC seams.