Abstract: A method for drilling a borehole includes selecting a lower pressure limit and an upper pressure limit for a drilling fluid at a drilling location in the borehole. In addition, the method includes activating a pump to circulate the drilling fluid down a drill string and up an annulus disposed about the drill string. Further, the method includes operating the pump to maintain the drilling fluid at the drilling location at a pressure between the upper and the lower pressure limits. Still further, the method includes deactivating the pump to stop circulating the drilling fluid up the annulus. The method also includes sealing the drilling fluid in the annulus at a selected time after deactivating the pump and maintaining the pressure of the drilling fluid at the drilling location between the lower and the upper pressure limits.

Abstract: Disclosed is a method and system for tuning a hydraulic model to be used for estimating down hole dynamic pressure as a function of flow rate includes: a) selecting a non-tuned hydraulic model estimating the relative magnitude of the pressure losses in various annulus sections of the well bore; b) applying the non-tuned hydraulic model to give a first order estimate of the pressure gradients and the shear stresses at the drill string; c) applying the same non-tuned model to estimate the flow lift area for two different flow rates, where the first flow rate is zero or much lower than the second flow rate being substantially equal to a typical flow rate obtained during drilling; and d) performing a model tuning test where the string is rotated off bottom while said two different flow rates are used to obtain corresponding string weights.

Abstract: Disclosed is a method and system for tuning a hydraulic model to be used for estimating down hole dynamic pressure as a function of flow rate includes: a) selecting a non-tuned hydraulic model estimating the relative magnitude of the pressure losses in various annulus sections of the well bore; b) applying the non-tuned hydraulic model to give a first order estimate of the pressure gradients and the shear stresses at the drill string; c) applying the same non-tuned model to estimate the flow lift area for two different flow rates, where the first flow rate is zero or much lower than the second flow rate being substantially equal to a typical flow rate obtained during drilling; and d) performing a model tuning test where the string is rotated off bottom while said two different flow rates are used to obtain corresponding string weights.

Abstract: A method for drilling a borehole includes selecting a lower pressure limit and an upper pressure limit for a drilling fluid at a drilling location in the borehole. In addition, the method includes activating a pump to circulate the drilling fluid down a drill string and up an annulus disposed about the drill string. Further, the method includes operating the pump to maintain the drilling fluid at the drilling location at a pressure between the upper and the lower pressure limits. Still further, the method includes deactivating the pump to stop circulating the drilling fluid up the annulus. The method also includes sealing the drilling fluid in the annulus at a selected time after deactivating the pump and maintaining the pressure of the drilling fluid at the drilling location between the lower and the upper pressure limits.