Borehole Wall Strengthening with Micron and Nano Materials in “Dabadong” Area of Changning

The Longmaxi formation in Changning is highly developed with microfractures because of the tectonic action in the “Dabadong” area and the formation rock components. The sizes of the primary pores are distributed in a range of 0.05-2 μm. The formation stability is very poor and overpull and resistance have been frequently encountered during drilling. Increase in mud weight only cannot control wellbore instability. The drilling fluids presently in use only contain micron-sized plugging agents and are unable to effectively plug the nanometer pores. The lack of nanometer plugging agents cannot help form low permeability plugging layers to hinder the transmission of borehole pressure into the formations. By introducing a nanometer graphene plugging agent, the drilling fluid has both micron-sized and nano-sized plugging agents. Furthermore, the mud weight was determined through geomechanics model. With all these technologies and mud property control, the borehole wall was strengthened. Application of the borehole wall strengthening technology in the well Ning-209H69 showed that the properties of the drilling fluid were stable, no downhole troubles were encountered in the whole drilling process, the average percent hole enlargement was less than 8%, and the borehole wall collapse was effectively eliminated.