Mechanism of High-Speed Cutting of Cement Plug by PDC Bit
When the coiled tubing is used in drilling,the bit is worn severely due to high weight on bit(WOB)and low rotation speed,resulting in poor milling effect of cement plug.In order to solve this problem,based on elastic-plastic mechanics and rock mechanics,taking the Drucker-Prager criteria as the cement strength criteria,by means of uniaxial and triaxial tests,the parameters of cement such as elastic modulus,Poisson's rati-o,internal cohesion and internal friction angle were obtained.The constitutive model of cement was built,and a 2D finite element model of high speed cutting of cement plug was built using ABAQUS software.On this basis,the influences of dip angle,cutting depth and cutting speed on the crushing specific energy were analyzed.The re-search results show that when the cement plug is cut at high speed,small and uniform debris is produced,while at low speed,massive or banded debris is produced.The dip angle(5°-25°)and cutting depth(1.0-2.5 mm)are positively correlated with the crushing specific energy,while the crushing specific energy decreases with the in-crease of cutting speed.When the cutting speed is 2.26 m/s,the crushing specific energy is the smallest,and the efficiency of crushing cement plug is the highest.The research results provide a theoretical support for the cutting of cement plug by PDC bit.
PDC bitlow WOBhigh-speed cuttingcrushing specific energydip anglecutting depthcutting cement plug
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