Research and application of drilling fluid with strong inhibition and sealing capacity

Wellbore collapse and lost circulation tend to happen during the drilling in Fauqi Block of Missan Oil field, Iraq. To deal with these difficulties, a new type of drilling fluid system with strong inhibition and sealing capacity was designed and developed in this paper. Based on the multi-component combination of KCl, sodium silicate and polyamine inhibitor, this system could inhibit shale hydration and dispersion effectively, and its shale swelling rate and capillary suction time are 67.6% and 64.4% lower than those in fresh water. Based on the combination of the physical sealing with chemical wall stabilization effect of silicate, the filtration loss of this system in low-permeability sand plugging test is only 9.6 mL. It is demonstrated that this system can seal the formation fractures and micro fractures effectively, reduce the intrusion of fi ltrate into the formation, enhance wellbore stability and avoid downhole leakage.This system was applied on site in the fi fth section of Well FQCS-41 in Missan Oil field, Iraq. It is indicated that its performance is stable with good rheological property in the process of drilling, and the borehole diameter is regular with average diameter enlargement rate of 1.2% in the fi fth section.