Formation Damage Prevention Drilling Fluids for Strong Water Sensitive Formation of Toutunhe Group in Fudong Oilfield

The reservoir of Jurassic Toutunhe Formation in Fudong Slope Area in Junggar Basin has strong water sensitivity which has created challenges in reservoir protection while drilling.To minimize the drilling fluid damage to the reservoir,the present organic salt drilling fluid system was optimized.Based on the organic salt drilling fluid system whose core components of main agent was a linear polymer-JN-2 with strong inhibitory,amine inhibitors and "ideal packing" bridging agent were added to improve the inhibitive ability and sealing capability of the system,thus achieving formation damage control during drilling.The drilling fluid was optimized through lab experiments.Experimental results showed that the rheological property of optimized drilling fluid system before and after aging was stable.HTHP filter loss was reduced from the original 12.6 mL to 8.0 mL.Shale expansion ratio was reduced from 20% to 17%.The recovery of shale was increased to 91.8% from 90.14%.Permeability recovery of natural reservoir cores increased to 82.15% from 73.14%.Results showed that the scheme of combination of amine inhibitors and "ideal pac-king" diversion agent could improve the drilling fluid inhibitive ability and sealing capability,making it a reasonable application and an effective technical means to protect highly water sensitive formation in the drilling process.