Laboratory studies on control coal bed methane formation damage by Fuzzy-Ball based drilling fluids

ZHENG Li-hui; MENG Shang-zhi; CAO Yuan; LI Zhong-feng

Abstract：0. 85 g/cm~3 drilling fluids of Fuzzy-Ball based was prepared by building-core agent,building-membrane agent,building-layer agent and location agent in laboratory. Inner Mongolia coal was grinded into coal dust with different mesh for simulating large, medium and slight porous media. Static filling & plugging testing was done by the coal dust, the backpressure was 0. 5 MPa. When driving pressure was 0. 5 MPa,KCl solution was leakoff entirely. However,Fuzzy-Ball based drilling fluids seal successfully when driving pressure was 5 MPa. Core plungers were drilled from the same coal,it is shown by dynamic and static rock core plugging testing that the leakoff rate of KCl water based solution become larger while the driving pressure increasing. The same test was done by Fuzzy-Ball based drilling fluids,the coal cores were sealed even when driving pressure was up to 6. 00 MPa. The return permeability of core after contaminated by KCl solution are less than 66%. Meanwhile,after sliced by 1.0 cm,the return permeabilities of core contaminated by Fuzzy-Ball based drilling fluids are large than 96%. Through laboratory tests,it is proved that Fuzzy-Ball based drilling fluid can seal coal formation and reduce formation damage greatly.