Patent ID: 6575244
Filing Date: 2003-06-10
Classification: E21B

Abstract:
A method of controlling one or more operating pressures within a subterranean borehole that includes a tubular member positioned within the borehole that defines an annulus between the tubular member and the borehole, a sealing member for sealing the annulus between the tubular member and the borehole, a pump for pumping fluidic materials into the tubular member, and an automatic choke for controllably releasing fluidic materials out of the annulus between the tubular member and the borehole, comprising:sensing an operating pressure within the tubular member and generating an actual tubular member pressure signal representative of the actual operating pressure within the tubular member; comparing the actual tubular member pressure signal with a target tubular member pressure signal representative of a target operating pressure within the tubular member and generating an error signal representative of the difference between the actual tubular member pressure signal and the target tubular member pressure signal; and processing the error signal to generate a set point pressure signal for controlling the operation of the automatic choke, wherein processing the error signal comprises: multiplying the error signal by a gain Kp; integrating the error signal and multiplying the integral of the error signal by a gain Ki; and differentiating the error signal and multiplying the differential of the error signal by a gain Kd.