Gas Lift State Estimation via Interpolation Module
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Solution Overview
Problem
Existing gas lift systems in oil and gas drilling face instability due to slug formation, which complicates down-hole measurements and control, making accurate state estimation challenging.
Innovation Solution
A multiple-model state estimation system using local linear models and an interpolation module to estimate down-hole process variables such as annulus pressure, tubing pressure, and lift gas rate without requiring direct down-hole measurements, by linearizing the gas lift system at multiple equilibrium points and incorporating estimates from multiple local state estimators into a single estimate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If down-hole measurements are implemented, then measurement precision improves, but device complexity and cost increase significantly
Solution Approach 1:
The patent uses surface measurements as an intermediary to indirectly obtain down-hole process variables. Instead of placing sensors directly in the harsh down-hole environment, the system uses easily obtainable surface pressure and flow rate measurements combined with a state estimator algorithm to compute down-hole conditions, thus avoiding the complexity of down-hole instrumentation while achieving accurate estimation
Solution Approach 2:
The patent replaces the mechanical measurement system (physical sensors and instrumentation in the down-hole environment) with a computational system. The state estimator algorithm processes surface measurements to mathematically reconstruct down-hole states, substituting complex mechanical measurement devices with software-based estimation
2Adaptability or versatility
If nonlinear state estimators are used to cover broader operating range, then adaptability improves, but computational complexity increases
Solution Approach 1:
The patent segments the complex nonlinear estimation problem into multiple simpler linear estimation problems. By dividing the operating range into multiple regions and creating a local linear model for each region, the system achieves broad adaptability while keeping each individual estimator simple and computationally efficient
Solution Approach 2:
The patent implements a dynamic model selection mechanism that adapts the estimator behavior to current operating conditions. The system dynamically selects which local linear model to use based on real-time surface measurements, allowing the estimator to adapt to changing operating conditions without requiring a single complex nonlinear model
3Productivity
If local linear models are used for state estimation, then computational efficiency improves, but measurement precision may deteriorate
Solution Approach 1:
The patent divides the operating range into multiple segments, each with its own local linear model. By segmenting the problem space, each linear model only needs to accurately represent a limited portion of the operating range, maintaining high precision within each segment while keeping computations simple and efficient
Solution Approach 2:
The patent uses multiple local linear models covering the entire operating range, providing slightly more computational effort than a single model would require. By distributing the estimation task across multiple specialized models rather than using one general model, the system achieves both efficiency and precision
Data Source
AI summary
A method and apparatus for estimating a down-hole annulus pressure, and/or a down-hole tubing pressure, and/or a down-hole lift gas rate through a gas injection valve of gas lift system, which comprises at least one gas lift choke and at least one gas injection valve and at least one production choke. A state estimator is proposed to obtain the values of these down-hole process variables. The estimator contains a number of local estimators and an interpolation module.