Abstract: Chiqian 1 well,in eastern Sichuan oilfield,T1j12 gas pay zone has high content of H2S that can’t be developed now,but T1j12 gas zone which has low content H2S can be produced.Tow zones pace 20 m and is easy channeling,so cement quality is important to development.To solve this problem,149mm diamond dual centers drilling bit and 152mm diamond coring bit are used and hole diameter increased by 19mm and 11mm separately.Over-cut rate are 12.8% and 7.3% separately,for cement quality created reliable condition.