Analysis and Application of Drilling Wellbore Stability of Ultra-Deep Reservoir in Kuqa Depression
The ultra-deep oil and gas reservoir in Rasu structural zone of Kuqa depression has the characteristics of large buried depth,high temperature,large lithologic change and high stress field,which leads to the inaccurate drilling mud density window based on the conventional wellbore stability analysis,resulting in frequent instability of the wellbore during the drilling process,and brings hidden dangers to drilling safety and environmental protection.By considering the influence of temperature effect on the borehole stress and adding the weak surface(fracture)instability condition based on Mohr-Coulomb destruction criterion,we proposed a method to determine the safe slurry density window of ultra-deep reservoir drilling according to six parameters:the minimum slurry density for shear instability and the maximum slurry density for tension instability in rock and weak surface,and the equivalent slurry density of pore pressure and minimum horizontal main stress.The application results of real data show that this method has good applicability and accuracy for the prediction of collapse pressure and leakage pressure in the ultra-deep complex formation in Bozi block of Kuqa depression,and can provide effective reference for the actual borehole drilling design.
wellbore stabilityultra-deep fracture gas reservoirborehole stressrock rupture criteria
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