Study On Plugging And Protecting The Borehole Wall Using Nano Particles

The borehole instability is one unsolved conundrum in the filed of drilling engineering.There is no one integrated and effective way studied to solve it so far.The borehole instability is not only concluding the brittle shall collapse,the plastic mud shall well bore shrinkage and viscoelastic strain,but also concluding the complicated situation caused by the pressure of drilling fluid.One statistics show that the vast majority of borehole instability accidents presented in mud shale which contain mature microcrack.Under the effect of a certain amount of pressure difference,the filter liquor of the drilling fluid flow into the stratum through the microcrack.The stratum will desquamate along the surface layer of the microcrack.One important method to enhance the stability of the borehole wall is taking advantage of nano-micron particles plugging material in drilling fluid.The nano-micron particles can plug the microcrack of the mud shall to prevent the filter liquor of the drilling fluid flowing into the microcrack.With the result that the mud shall hydration expansion power can be reduced and prevented transmitting.According to the mechanism of borehole instability and the method of plugging the microcrack,we optimize five kinds of nano-micron particles plugging material.We analyze and characterize these nano-micron particles plugging material using scanning electron microscope and size distribution measurement.Relying on the result of artificial mud cake experiment,sand bed plugging experiment,wave velocity in rock debris experiment and scanning electron microscope,we test the plugging capacity and mechanism of these plugging materials The result shows that these nano-micron particle plugging materials can plug the microcrack of the mud shall effectively.On the basis of treating chemical optimize and making use of a serious of performance evaluation,we develop the recipe of nanometer plugging drilling fluid.The experimental results show that this recipe of nanometer plugging drilling fluid possesses ideal rejection capability,rheological prorerty,lubricating property and antipollution property.This drilling fluid system can resist temperature 150?,antipollution up to 6%of NaCl,CaCl₂antipollution up to 0.5%,anti-contaminated of drilling cuttings capacity up to 6%,system lubrication coefficient 0.112,drilling cuttings recovery rolling up to 91.16%,24h core linear expansion is only 4.1mm.This system possesses well-deserved plugging performance.The filter loss of 150?HTHP with ordinary filter paper is 12.4 mL,and with nanometer filter paper is only 10.6 mL.This recipe of nano plugging drilling fluid has been applied in the drilling site of TH12560X.They have drilled out the stratum of hard brittle shale through this process,it shows that this recipe possesses ideal plugging property.One technology used in drilling site about nano-micron particle plugging materials formed preliminarily.