Plugging Inhibitive Drilling Fluid Used in Longfengshan Gas Field

The Quantou Formation and the formations above in Longfengshan gas field are mainly water sensitive shales. Downhole troubles such as borehole wall collapse, pipe sticking, wellbone expansion and bit balling have frequently been encountered in drilling these formations. Lost circulation, on the other hand, has always been encountered in the Yingcheng Formation, which is full of fractures. To ensure safe drilling through these formations, a plugging inhibitive drilling fluid was formulated based on laboratory researches. A shale inhibitor, NK-1, was selected through shale core swelling test and bentonite hydration test. KFT-II and ZX-8, as plugging agent and anti-collapse agent, were selected through mud cake building test and core permeability experiment. Laboratory evaluation showed that this drilling fluid had stable rheology, good filtration characteristics, strong inhibitive capacity and plugging and anti-collapse performance. In field application, the well Bei-209 was drilled successfully with this drilling fluid. The drilling fluid had stable rheology, and no borehole wall collapse happened. Tripping of drill string, wireline logging and casing running were run with no hindrance, and the reservoir formations were fairly protected from being damaged.