Drilling technology of Well M-2 in Matouying dry hot rock of Tangshan

Well M-2 is a production well of Matouying dry hot rock mining test well group, and the key techniques during drilling were studied to solve the problems of Cenozoic Formation collapse, bit balling, low drilling efficiency of Archaean granite formation, overflow, block falling and high temperature drilling fluid. The wellbore stability of Cenozoic Formation was maintained by increasing the specific gravity of drilling fluid, reducing fluid loss, and increasing viscosity. The problem of bit balling in Neogene Formation was solved by using double pumps with large displacement and high rotary speed. The overflow, large consumption and block loss were effectively prevented in the well depth of 3 880 m, through the increasement of mud gravity and the addition of plugging agent. By ameliorating the high-temperature resistant drilling fluid, the rheology property of sludge was improved and the friction and rotary torque were reduced, which guaranteed the success of Well M-2 completion. The average drilling speed of Well M-2 in Archaean metamorphic granite formation reached 2.46 m/h, which was 69.7% higher than that of Well M-1 in the same formation, and the drilling cost was reduced by changing the drilling assembly and using drilling tools with large screw, large drilling weight, large displacement and coarse diameter. This method can effectively improve the drilling efficiency by the rotary hammer and PDC bit speed increase experiment. However, the metamorphic granite formation is hard and abrasive, PDC pieces would easily collapse, hence the bit performance still needs to be improved. The overall benefit of assemblage of ϕ203 mm screw and roller cone bit was higher, which can be used as the optimal scheme in subsequent construction.