Babalola, Shola Daniel (2015-12). Effect of Mud Cake and Temperature on Wellbore Collapse Initiation Pressure Using Different Failure Criteria. Master's Thesis. Thesis uri icon

abstract

  • Accurate wellbore collapse initiation pressure is necessary for a robust wellbore bridging study. When drilling overbalance through a porous and permeable formation, there is flow of wellbore fluid into the formation, leaving behind a solid mud cake on the formation. Formation strengthening by drilling fluids has been discussed extensively in the literature. This work attempts to study the coupled effect of mud cake and temperature on the collapse initiation pressure. Sensitivity analysis using unequal horizontal stresses showed that the effect of mud cake on collapse initiation pressure is not affected by the mud cake compressibility but depends on mud cake thickness, rock unconfined compressive strength, stress level/magnitude and wellbore size. The presence of a mud cake reduces the collapse initiation pressure, making the formation more resistant to collapse. This effect increases as the mud cake thickness, unconfined compressive strength and stress level increase. A decrease in wellbore size also increases the effect of filter cake on collapse initiation pressure. Generally, wellbore heating weakens the formation while cooling strengthens the formation. The presence of a mud cake acts similarly to cooling the wellbore. Coupling the effect of mud cake and temperature showed that the presence of mud cake increases the effect of both wellbore heating and cooling.
  • Accurate wellbore collapse initiation pressure is necessary for a robust wellbore bridging study. When drilling overbalance through a porous and permeable formation, there is flow of wellbore fluid into the formation, leaving behind a solid mud cake on the formation. Formation strengthening by drilling fluids has been discussed extensively in the literature. This work attempts to study the coupled effect of mud cake and temperature on the collapse initiation pressure.

    Sensitivity analysis using unequal horizontal stresses showed that the effect of mud cake on collapse initiation pressure is not affected by the mud cake compressibility but depends on mud cake thickness, rock unconfined compressive strength, stress level/magnitude and wellbore size. The presence of a mud cake reduces the collapse initiation pressure, making the formation more resistant to collapse. This effect increases as the mud cake thickness, unconfined compressive strength and stress level increase. A decrease in wellbore size also increases the effect of filter cake on collapse initiation pressure.

    Generally, wellbore heating weakens the formation while cooling strengthens the formation. The presence of a mud cake acts similarly to cooling the wellbore. Coupling the effect of mud cake and temperature showed that the presence of mud cake increases the effect of both wellbore heating and cooling.

publication date

  • December 2015