控压钻井井下不可测变量的非线性估计

控压钻井井下流量和压力的变化是判断井下工况的重要标志。从准确估计井下流量和压力的角度出发，以井筒为对象建立井下三阶动态模型，该模型中含有未知参数和未知状态，模型中摩擦因数项作为未知参数变量，井下流量和压力作为未知状态变量。以此模型为基础，建立李雅普诺夫函数，设计一种全新的非线性状态观测器，估计井下未知参数和未知状态，同时保证观测器估计误差收敛到零。利用钻井数据和井筒模拟器，分别在不存在建模误差和存在建模误差的条件下对非线性状态观测器进行仿真，两种条件下的仿真结果表明，该观测器均能够快速、实时、准确地估计井下流量和压力。

Nonlinear estimation of the down-hole unmeasurable variables in the managed pressure drilling system

The change of down-hole flow and pressure is an important symbol that has used to determine down-hole drilling condition in managed pressure drilling. Based on the accurate estimation of down-hole flow and pressure, a three-order down-hole dynamic model was established taking wellbore as the subject, which has unknown parameters and unknown states. In this model, friction factor is the unknown parametric variable, and down-hole flow and pressure are the unknown state variables. Based on this model, a Lyapunov function was established to design a new nonlinear state observer which can estimate down-hole unknown parameters and unknown states, thus ensuring that estimation error of the observer can be converged to 0. Using drilling data and a wellbore simulator, the nonlinear state observer was simulated under the condition of model error or no model error. The simulation results under the two conditions show that the observer can estimate down-hole flow and pressure in real time rapidly and accurately.