Aimed at resolve the several problems which affect drilling efficiency, such as balling up and calcareous cementation, the design of blade bits was modified.

Practical tests show that the performance of cemented carbide anvils, coated blade and drill bits with graded structure developed in this dissertation are superior to those with regular structure.

Based on the theoretical analysis, a new type of blade bit was invented. And this kind of bit combines the advantages of PDC bits and drag bits. And a series of field experiments were performed.