J. Marrelli

Optimal Control Strategy and Experimental Investigation of Gas/Liquid Compact Separators

This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Abstract The deployment of the new technology of gas-liquid compact separators such as Gas Liquid Cylindrical Cyclone (GLCC 1) requires dedicated control systems for field applications. The control strategy implementation is crucial for process optimization and adaptation, especially when GLCCs are operated at wide range of liquid and gas flow conditions. In this study, a unique and simple control strategy, which is capable of optimizing the operating pressure and adapting to liquid and gas inflow conditions, has been developed. Detailed simulations and experimental investigations have also been conducted to evaluate the performance of the proposed control systems. The significant advantages of this strategy are: the system can be operated at optimum separator back pressure; the system can adapt to the changes of liquid and gas flow conditions; and the strategy can be easily implemented using simple PID controllers available in the market. This provides the oil and gas industry a simple, robust compact separator control technique which has the potential for offshore and subsea applications. Introduction Compared to conventional separators, compact separators, such as the Gas-Liquid Cylindrical Cyclone (GLCC) are simple, compact, possess low weight, low-cost, require little maintenance, and are easy to install and operate. GLCCs have been used to enhance the performance of multiphase meters,

Performance and Control of Liquid-Liquid Cylindrical Cyclone Separators

The feasibility of using Liquid-Liquid Cylindrical Cyclone (LLCC© ) as a free water knockout device for bulk separation of oil-water mixtures in the field strongly depends on the implementation of control systems due to its compactness, less residence time and possible inlet flow variations. In this investigation, the LLCC control dynamics have been studied extensively both theoretically and experimentally. A linear model has been developed for the first time for LLCC separators equipped with underflow watercut control, which enables simulation of the system dynamic behavior. A unique “direct” control strategy is developed and implemented, capable of obtaining clear water in the underflow line and maintaining maximum underflow rate. Dedicated control system simulations are conducted using Matlab/Simulink® software to simulate the real system dynamic behavior. Detailed experimental investigations are conducted to evaluate the system sensitivity and dynamic behavior of the proposed control strategy. The results demonstrate that the proposed control system is capable of controlling the underflow watercut around its set point by obtaining maximum free-water knockout for a wide range of flow conditions. (inlet water concentration of 40% and an inlet mixture velocity of 1.5 m/s).Copyright

Differential Dielectric Sensor Model and its Applications for Water and Oil Flow

As a composition measurement tool, Differential Dielectric Sensor (DDS) developed by Chevron, has been investigated by several authors both theoretically and experimentally since 1989. The previous generation of DDS was based on empirical models which are produced time-consuming and labor-intensive. Uncertainty and repeatability are always issues limiting the application of empirical models. If parameters such as sensor geometries or properties of materials are modified in order to improve and/or optimize, the whole development process of the empirical model has to be repeated. In this paper, measurement model of DDS is developed with integrating 2 sub-models: dielectric mixture model and DD sensor model. The dielectric mixture model, taken from literature, outputs the effective dielectric permittivity of a two-component mixture. The development of DD sensor model is the main focus of this paper. Given effective permittivity provided by dielectric mixture model, DD sensor model predicts attenuation and phase shift of the transmission signal from transmitter to receiver. The measurement model is validated by experimental data and good agreement is observed.© 2010 ASME

The State-of-the-Art of Gas-Liquid Compact Separator Control Technology: From Lab to Field

Conventional gas-liquid separators are vessel-type with simple level, and pressure control since the residence time is large. Compact gas-liquid separators, such as Gas-Liquid Cylindrical Cyclone (GLCC© ), have emerged recently as alternatives to reduce size and increase separation efficiency for offshore and subsea applications. As compared to the vessel-type separators, compact separators, are simple, low-cost, low-weight, require little maintenance and are easy to install and operate. However, the residence time of the GLCC is very small. Consequently, it can get upset easily due to high flow variations at the inlet, for example, slugging, without the aid of fast and accurate control systems. In the past, lack of understanding of control system dynamics and design tools have prevented this technology from fast field deployment. The objective of this study is to present a review of the compact gas-liquid separator (GLCC) control technology. This includes the development of control strategies, control system design, dynamic simulation, experimental investigation and field applications. The performance of compact gas-liquid separator (GLCC) strongly depends on the liquid level and/or separating pressure. In this investigation, several control strategies have been developed for field applications of gas-liquid compact separators. Especially, an optimal control strategy was developed for handling slug flow and optimizing the system performance in terms of reduced or eliminated liquid carry-over (LCO) or gas carry-under (GCU). The developed strategies have been used for the design of several GLCC applications, currently in operation in the field. Details of these applications are also presented. This study provides the state-of-the-art of gas-liquid compact separator control technology from the lab to field.Copyright

Use of Multiphase Meters in Process Control for Oil Field Well Testing: Performance Enhancement Through GVF Control

First oil production from a deep-water oil field is to be achieved by the installation of an Initial Development System (IDS). Well testing is required for field development and reservoir management. The well testing system requires high accuracy oil and water rates to provide the data needed for decision analysis in ongoing drilling programs. The well testing system must also be integrated with other platform operations such as well clean up after drilling. The concept of a certain type of multiphase meter in a feedback control loop with conventional separation technology for process control is simulated to extend the capabilities of both technologies. The principle of GVF control as a supplementary to level control system has been developed for performance enhancement of oil field well testing. Concepts demonstrated here can also be easily applied as retro-fits to existing separation facilities which show accuracy or upset problems because of the simplicity and compact size of the additional multiphase meter component and non-disruptive supplementary integration with existing level control systems.Copyright

Intelligent Control of Compact Multiphase Separation System (CMSS©)—Part I: Modeling and Simulation

Performance of compact separators depends on implementation of stable and robust control strategies that are suited for specific applications. In this investigation, an intelligent control system has been developed for Compact Multiphase Separation System (CMSS© ) which consists of integrated configurations of three compact separators, namely, Gas-Liquid Cylindrical Cyclone (GLCC© ), Liquid-Liquid Cylindrical Cyclone (LLCC© ) and Liquid-Liquid Hydrocyclone (LLHC). This is a two-part paper, the first part (current paper) deals with the Modeling and Simulation of the CMSS© and the second part deals with Experimental Investigation. The specific objective of this CMSS© configuration is to knock out free water from the upstream fluids. In mature oil fields, water handling poses a huge problem. Thus water knock out at the earliest stage helps in significant cost savings. A novel fuzzy logic control system has been designed and tested for change in set-point of differential pressure ratio in LLHC. Dynamic models have been developed for each of the above mentioned control systems for design of stable PID parameters. A dynamic simulation platform (DSP) has been developed based on these models in Matlab/Simulink™ for predicting the transient performance of the integrated system. Steady state mechanistic models of individual devices are integrated to the Matlab/Simulink™ platform using look up tables to predict the overall response of the CMSS© for different scenarios.Copyright

Intelligent Control of Compact Multiphase Separation System (CMSS©)—Part II: Experimental Investigation

In this investigation, an intelligent control system has been developed for Compact Multiphase Separation System (CMSS© ) which consists of integrated configurations of three compact separators, namely, Gas-Liquid Cylindrical Cyclone (GLCC© ), Liquid-Liquid Cylindrical Cyclone (LLCC© ) and Liquid-Liquid Hydrocyclone (LLHC). This is a two-part paper, the first part deals with the Modeling and Simulation of the CMSS© and the second part (current paper) deals with Experimental Investigation. A new dual differential pressure sensor system has been implemented and tested for GLCC© , to eliminate the error in liquid level measurement due to change in watercut. A new watercut based control system using downstream pump speed control has been designed and tested for the LLCC© system. A new cascaded control strategy for change in set-point of differential pressure ratio using underflow quality from hydrocyclone has been designed and developed. Comparison of CMSS© performance simulator and experimental results shows that the control system simulator is capable of representing the real physical system and can be used to validate the controller design. Fuzzy logic controller has been successfully implemented and tested. Experimental results show a similar trend as the dynamic simulator results for the various input conditions and scenarios. The results from theoretical and experimental studies have shown that Free Water Knock Out (FWKO) CMSS© system can be readily deployed in the field using the control system strategies designed, implemented and tested in this study. Reliability analysis for FWKO CMSS© system has been conducted. System reliability has been calculated from reliability of components and performance reliability of the system. A new protocol has been introduced to calculate performance reliability based on performance failure of the system from simulation data. This protocol has been proven to predict performance reliability of a new system which does not have prior information on failure of components or devices.Copyright

A Modular Differential Dielectric Sensor (DDS) for Use in Multiphase Separation, Process Measurement and Control—Part I: Analytical Modeling

Oil industry increasingly demands accurate and stable continuous measurement of the percent water in crude oil production streams (watercut) over the entire 0 to 100% range. High accuracy and stability are also required for surface measurement to support niche applications such as control of processes which remove trace amounts of oil and particulates from produced water prior to disposal. Differential Dielectric Sensors (DDS) have been developed by Chevron as independent tools connected with multiphase meters for process management and composition measurement. This paper is a two-part paper — the first part (current paper) deals with analytical modeling of the DDS (configured in a single ended mode) and the second part discusses the results of key experimental investigations obtained in a differential mode. The main objective of this paper is to develop appropriate mathematical models for the DDS which characterize the microwave attenuation and phase shift as a function of fluid properties, sensor geometry and operational conditions. Forward models based on the analysis of microwave propagation have been developed for sensors configured as circular waveguides. Results of this project will be useful for optimization and refinement of multiphase meters.Copyright

A Modular Differential Dielectric Sensor (DDS) for Use in Multiphase Separation, Process Measurement and Control—Part II: Experimental Investigation

Accurate and continuous measurement of the percent water in crude oil production streams (watercut) over 0 to 100% range is critical for petroleum industry. High accuracy and stability are also required for surface measurement to support process control applications aimed at removing trace amounts of oil and particulates from produced water. This paper is a two-part paper — the first part [1] deals with analytical modeling of the Differential Dielectric Sensors (DDS) and the second part (current paper) discusses the results of key experimental investigations. A dedicated closed-loop experimental facility is used to obtain in-line real-time measurement of DD sensor data in a controlled configuration. A complete description of test facility is presented followed by detailed experimental results. The results show that DDS is unique in its use of very low noise and high sensitivity differential measurements between two identical sensors. In a process control system, DDS shows good measurement stability and is adaptive to composition measurements compensating for changes in oil composition, gas fraction, emulsion state, water NaCl concentration, temperature, and flow rate. Because of its auto calibration capability, DDS can also conduct real time calibration for sensor configuration changes caused by factors such as corrosion and erosion.Copyright