Drilling technology of T-shaped well in deep coalbed methane

In order to solve problems,such as the large window and curvature radius in conventional sidetrack drilling, small drilling bit in radial horizontal well with hydraulic jetting, and short drilling footage in coal seam, T-shaped horizontal drilling technology with flexible drilling tools has been developed. Its resultant window is only 20 cm and curvature radius ranges from 1.8/2.5 m. Using the superposition whip stock, multilayers can be targeted by multi-branch horizontal drilling once. With ø112 mm of sidetrack hole in ø139.7 mm casing, the drilling of horizontal well with ultrashort radius and large size is realized. The wellbore stability analysis demonstrates that the stability of the drilling of kick-off and horizontal sections can be guaranteed with only clean water +2% KCl. According to the torque analysis, the flexible drilling tools would not be destroyed with bending failure during rotatory drilling, drilling down or pulling out the hole, which permits 100 m of safety drilling. The analysis of hydraulic parameters shows that the pump delivery of 0.5～0.7 m3/min can meet the requirement of borehole cleaning and fast rock cracking. An industrial test in Linxing-Shenfu gas field using this technology has been conducted. It is the first deep CBM T-shaped well with six branches, three branches in each of two layers of coal seam. At present, the target depth is around 1 900 m with total horizontal footage is up to 478 m, among which the horizontal footage of four branches has exceeded 100 m.