The previous drilling practice showed that there were many drilling difficulties in igneous rock, such as less footage of one bit, lower roundtrip ROP, more tripping times, etc., which severely influenced the exploration and development process of carboniferous formation. After analysis, the reasons are mainly as follows: (1) Igneous rock has high hardness and poor drillability, which generally led to the few footage for tricone bits. (2) Igneous rock has complex lithological characters and

more »

... homogeneity, which resulted in the limited use of PDC bits. (3) The formation dip angle of piedmont tectonic belt in BH block is big, which made well deviation grow fast. Through analyzing its adaptability when drilling in igneous rock, the torsional impact tool can convert part of drilling fluid energy into the impacting downhole mechanical rock-breaking energy with a certain frequency and circumferential torsion and directly transmitted to the drill bit, so the stick-slip phenomenon of PDC bits can be eliminated effectively, the problem of limited use about PDC bits in igneous rock was solved, and the ROP in igneous rock can be enhanced. Through firstly used in igneous rock of Well BH1, the torsional impact tool continuously worked 649h with 457.5m of drilling footage on one trip. Compared with the drilling situation of adjacent upper igneous rock, the roundtrip ROP that was 0.7m/h was increased by 45.8 percent and at least 11 trip time and bit cost were saved. So the compound drilling technique with high efficiency PDC bit and torsion impact tool was an effective way to realize optimal and fast drilling in igneous rock formation.