Density of completion fluid for ultra deep wells in long naked eye horizontal sections analysis of the importance of wellbore stability
Completion-fluid density is essential for borehole stability in deep marine openhole horizontal wells with the horizontal length over 2,000 m due to long cycle time and complex string structure highly needed for the stability whose re-lation to both trajectory azimuth and borehole inclination should be taken into account.Therefore,the influence of produc-ing pressure differences on the stability was analyzed for those wells with or without fractures through numerical simulation and two Drucker-Prager criteria to estimate both strength failure and effective plastic strain.In addition,one method for density evaluation was created for stability assurance.Results show that(i)there exists the best stability in some horizontal wells without fractures along the direction of maximum principal stress,and this stability is increased with the increased in-clination;and(ⅱ)there exists the most stable wells in the others with fractures whose dip of 90° goes the maximum princi-pal stress.The fracture strike that moves to the direction of the stress from that of minimum stress makes the stability somehow better.And this borehole stability grows with the increased dip.In fact,this method has been applied to Pz3-4D well successfully to verifying simulation ending,which may provide a novel solution for stability improvement in deep open-hole horizontal wells.
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