Patent ID: 9638031
Date: 2017-05-02
CPC Classifications: E21B

Claim:
1. A method implemented with a controller coupled with memory devices having instructions code stored thereon for controlling well bore pressure, the controller including a computer equipped with capability for processing algorithms, evaluating polynomials and computing mathematical equations included with the stored instructions, wherein the instructions when executed by the computer, implement the method steps, comprising: detecting a well bottom pressure, a stand pipe pressure, a vertical casing pressure, an injection flow rate and an outlet flow rate during construction process; determining presence of overflow or leakage; if there is no overflow or leakage, then fine-adjusting the wellhead casing pressure according to a difference values between the well bottom pressure, the stand pipe pressure, the casing pressure and target pressures thereof, or the slight fluctuations of the well bottom pressure, the stand pipe pressure, or the casing pressure, so as to ensure that the well bottom pressure, the stand pipe pressure, or the casing pressure are at set values, wherein adjusting amount is optimized according to a conventional model prediction control algorithm, so as to calculate a control objective parameter of a next moment; if there is overflow or leakage, then using a well bore single-phase or multi-phase flow dynamic model to simulate and calculate the overflow or leakage position and starting time of the overflow or leakage, predicting the variation over a future time period of the well bore pressure in the well drilling process, and utilizing an optimization algorithm to calculate the control parameter under a minimum of an actual well bottom pressure difference during a future period; and repeating the optimization process for the next time period after a first control parameter is selected and set; (1) wherein a prediction control equation of the single-phase or multi-phase flow dynamic model is expressed by the following formula: wherein f {right arrow over (x)}(t) represents a state vector at a moment of t, including the casing pressure; u(t) represents the casing pressure at the moment of t; y(t) represents the well bottom pressure at the moment of t; and e (2) wherein an error between an actual measurement casing pressure and a prediction calculation casing pressure is a prediction error e(k+i), wherein y (3) wherein a predicted value e(k+i) at a moment n+i in the future is estimated by a polynomial error fitting method based on values at a given moment, wherein the predicted value e(k+i) comprises an error at a moment k and a revised error, wherein during this process (L>l2>1), and when L=l2 wherein e(k) is an error at the moment k; β l