Abstract: There is described a drilling fluid for wellbore strengthening having nanoparticles and granular particles. In one aspect described herein, the drilling fluid is an invert emulsion based fluid. In a further aspect, the nanoparticles are iron hydroxide or calcium carbonate, and in a further aspect from about 1 to 30 nm in size. In one aspect described herein, the granular particles are graphite or calcium carbonate and in a further aspect, up to 250 ?m in size. The nanoparticles and granular particles plug fractures in the wellbore to strengthen the wellbore.

Abstract: There is described a drilling fluid for wellbore strengthening having nanoparticles and granular particles. In one aspect described herein, the drilling fluid is an invert emulsion based fluid. In a further aspect, the nanoparticles are iron hydroxide or calcium carbonate, and in a further aspect from about 1 to 30 nm in size. In one aspect described herein, the granular particles are graphite or calcium carbonate and in a further aspect, up to 250 ?m in size. The nanoparticles and granular particles plug fractures in the wellbore to strengthen the wellbore.