Self-Balancing Mixing Control for Cement Slurry
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Solution Overview
Problem
In hydrocarbon well bore servicing, existing control systems face challenges in maintaining consistent cement mixture quality and flow rates due to limited instrumentation, particularly for powdered solids like cement, and supply constraints such as interruptions or blockages, which can lead to defective cement being pumped underground without detection.
Innovation Solution
A control system with multiple actuators and a logic circuit that adjusts the flow rates of materials and the discharge rate of the mixture to maintain desired properties and flow rates, even in the presence of supply constraints, by using virtual flow rate control and density estimation to manage the mixing and pumping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If limited instrumentation is used for measuring flow rates of powdered solids like cement, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent introduces an intermediary measurement approach by using easily measurable parameters (water flow rate, electrical conductivity, density) to indirectly determine the flow rate of powdered cement. Instead of directly measuring solid flow rate with complex instrumentation, the system uses these intermediary measurements combined with mass balance calculations to infer the cement flow rate, thereby avoiding complex solids flow meters while maintaining measurement precision.
2Productivity
If supply constraints such as interruptions or blockages occur, then productivity is reduced, but reliability of mixture quality control deteriorates
Solution Approach 1:
The patent implements a feedback control system that continuously monitors mixture density and electrical conductivity, compares these measurements with target values, and automatically adjusts the water and cement flow rates to maintain desired mixture quality. This closed-loop feedback ensures that even when supply constraints occur, the system can detect quality deviations and correct them, maintaining reliability of mixture quality control while managing productivity impacts.
Solution Approach 2:
The system performs preliminary actions by pre-establishing target density and composition values, and having the control system ready to immediately adjust flow rates when deviations are detected. The control algorithms are pre-configured to respond to various supply constraint scenarios, enabling rapid correction before quality defects propagate through the system.
3Device complexity
If manual monitoring and intervention are used to detect supply constraints, then device complexity is reduced, but loss of time increases
Solution Approach 1:
The control system continuously and automatically monitors mixture properties through density and electrical conductivity sensors, providing real-time feedback without requiring manual intervention. This automated feedback loop immediately detects supply constraints and triggers appropriate control actions, significantly reducing both detection time and response time compared to manual monitoring methods, while the complexity is managed through standardized control algorithms.
Data Source
AI summary
Methods for controlling the in-feed and discharge rates of materials flowing into and out of a mixing process where one priority is to achieve a target mixture flow rate from the mixing process and another priority can be to achieve a target value for a mixture property. Actuators can be operated to control material in-feed rates, the mixture composition, and discharge rate, and can maintain a hold-up of the mixture in the mixing process. A total flow rate controller provides a control signal to a controller acting on the discharge rate and a controller acting on the in-feed rates. The mixture discharge flow rate can be automatically reduced from its desired target when the commanded rate of at least one of the materials exceeds its available supply rate as inferred from an inability to maintain the targeted value for the mixture property.