METHOD AND APPARATUS FOR CONTROLLING THE FLOW OF DRILLING FLUID IN A WELLBORE

摘要

ABSTRACT OF THE DISCLOSUREA method for controlling the flow of drilling fluid through asubaqueous wellbore is disclosed. The method comprises the steps ofcontinuously measuring the output flow rate (A) of the drilling fluidfrom the wellbore, the input flow rate (B) of the drilling fluid to thewellbore, and at least a component of the pitch and roll (P/R) of thevessel, computating a floating alarm limit (C) dependent upon the pitchand roll (P/R) signal and the roughness of the sea, filtering the periodicfluctuation of the output flow rate (A) due to the motion of the vessel,and computating the delta flow signal (D) by subtracting the input flowrate (B) from the filtered output flow rate (A). The method furthercomprises the step of generating a signal whenever the absolute value ofthe delta flow rate (D) exceeds the floating alarm limit (C) to providea visible warning that the flow of drilling fluid is out of control andto either close off the wellbore in case of a kick or to stop the flowof fluid and stop drilling in case of lost returns.Apparatus for controlling the flow of drilling fluid through asubaqueous wellbore is disclosed while drilling from a floating vessel.The wellbore is connected to the lower end of the drill string and thelower end of an annulus by a valve through which the drilling fluidflows. The upper end of the annulus is connected to a conduit fromwhich the drilling flows to the suction side of a pump which circulatesthe drilling fluid therefrom into the upper end of the drill string,through the wellbore, and back up the annulus into the conduit. Theapparation comprises an output flow meter connected to the exit of theconduit, an input flow meter connected between the pump and the upperend of the drill string, means mounted on the vessel for sensing thepitch and roll of the vessel, and computer means for receiving theoutput flow rate (A) signal from the output flow meter, the input flowrate (B) from the input flow meter, and the pitch and roll (P/R) signalfrom the pitch and roll sensing means. The computer means calculates analarm limit (C) based on the pitch and roll (P/R) signal and the roughnessof the sea continuously filters the periodic fluctuation of the outputflow rate (A) due to the motion of the vessel, computes the delta flowsignal (D) by subtracting the input flow rate (B) from the filteredoutput flow rate (A), and generates a signal whenever the delta flowrate (D) exceeds the floating alarm limit (C) to provide a warning of apossible blowout or lost circulation condition and to either close offthe wellbore in case of a kick or to stop the flow of fluid and stopdrilling in case of lost returns.