Antileaking and Lost Circulation Control Technology for Deep Coalbed Methane Well in the Yanchuannan Block

The Yanchuannan Block possesses rich deep coalbed methane resources but has serious lost circulation problems during the drilling process. In order to reduce the frequency of the occurrence of lost circulation, minimize the economic losses induced by lost circulation, and ensure the safe and efficient development of coalbed methane wells,we developed a anti-leaking and lost circulation control technology. Based on the analysis of the geological characteristics and the lost circulation mechanism, the new technology incorporated plugging-while-drilling fluids and pressure-bearing plugging process was proposed. In the Yanchuannan Block where the upper formations develop pores, pore-type lost circulation predominates, 5% composite plugging materials are added to the drilling fluid for lost circulation control. The lower formations develop natural fractures, and are dominated by fracture-type lost circulation, accordingly 7% composite plugging materials are added to the plugging-while-drilling fluids for leakage prevention and plugging. For the formations where fractures can easily propagate, plugging-while-drilling fluids with 10% composite plugging materials were applied for plugging. In order to solve the problems that some coalbed methane wells have no blowout preventer or that the blowout preventer can’t perform pressure-bearing plugging, a packer with simple rubber plug at the wellhead was developed, which formed the pressure-bearing anti-leaking and lost circulation control technology for coalbed methane wells. After applying the technology to the deep coalbed methane wells in the Yanchuannan Block, the lost circulation rate was reduced from 41.53% to 23.07%, and the treatment time of lost circulation was also greatly shortened. The results also indicated that the proposed technology can lower the lost circulation rate of deep coalbed methane wells in the Yanchuannan Block, shorten drilling cycles, reduce the drilling cost, and improve the development benefits of coalbed methane in this block.