Methodology for Solving Control Loop Problems

This time of year, after our big Emerson Exchange conference, I like to go back and see what sessions I missed to be able to be able to recap for you.

Mark Coughran Process Control Consultant

Mark Coughran
Process Control Consultant

I caught up with Emerson’s Mark Coughran, whom you may recall from many control performance-related posts. He co-presented a paper, Solve Control Loop Problems for Smooth Oil & Gas Production with Emerson’s Gergő Kertész. I also live-blogged a presentation by Gergő during the conference.

They described several examples where control performance problems degraded oil & gas production operations or distracted operators. Mark and Gergo shared the methodology developed by the Control Performance consultants which they applied to examples presented.

The most common issue they see are loops put in manual mode because they oscillate when placed in automatic mode. Many sites, especially in remote locations, do not have personnel trained to diagnose and correct such problems. Mark highlighted the importance of isolating the problem to a particular component of the loop, preferably without going to the field for time-consuming (and possibly hazardous) examination and testing.

Some common issues causing these oscillatory conditions are PID loop tuning values, poor performance of the loop’s control valve and the control strategy applied. Continue Reading

Integrated Reservoir Engineering

The science of modeling oil & gas reservoirs involves a mix of the natural sciences. Wikipedia defines reservoir engineering as:

…a branch of petroleum engineering that applies scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs so as to obtain a high economic recovery. The working tools of the reservoir engineer are subsurface geology, applied mathematics, and the basic laws of physics and chemistry governing the behavior of liquid and vapor phases of crude oil, natural gas, and water in reservoir rock.

Managing uncertainty and accurately predicting how the reservoir will perform improves the economic yield and the decisions supporting the development of the oil and gas wells.

One of the news items during the Emerson Exchange conference was the announcement of enhancements to the Roxar Tempest 7.1 reservoir engineering software suite. The press release summed up the enhancements:

The new software comes with major enhancements to its uncertainty management and reservoir prediction features within the software module Tempest ENABLE, allowing users to create ensemble-based prediction workflows and better quantify uncertainty in production forecasts. Tempest 7.1 also comes with significant advances to its Tempest MORE reservoir simulator and Tempest VIEW, the pre and post-processing interface for all Tempest modules.

The new innovations in Tempest ENABLE are the first commercial results of the three-year Total Uncertainty Management program… They also build on the long-term collaboration with the Department of Mathematical Sciences at the UK’s Durham University on the development of statistical algorithms.

Noted Emerson’s Kjetil Fagervik:

Kjetil Fagervik Managing Director, Emerson’s Roxar Software Solutions

Kjetil Fagervik
Managing Director, Emerson’s Roxar Software Solutions

Tempest 7Generating accurate future production estimates, quantifying uncertainty, and minimizing financial risk represent three of the industry’s greatest challenges… Our new version of Tempest meets these challenges head-on, providing users with the necessary statistical rigor and capabilities to generate accurate and realistic production scenarios, test multiple realizations, and better quantify uncertainties on volumes and cumulative production. We were always confident that the Total Uncertainty Management program would deliver strong commercial benefits and in Tempest 7.1 we are starting to see the results.

Continue Reading

Control Valve or Pressure Regulator?

Pressure is typically one of the most fundamental control parameters for process manufacturers and producers. Many types of final control elements including control valves and pressure regulators are used to perform this function. How do you decide which to use?

Jake Buford

Jake Buford
Regulator Product Specialist

I received an advanced copy of a paper being developed by Emerson’s Jake Buford. The paper, Choosing the Proper Pressure Control Device for your Application, does a great job of describing the differences and considerations in your selection process.

He opens highlighting the differences between control valves and pressure regulators:

Control valves are defined as valves that open and close in response to signals that are monitoring a specific process variable. Examples of these variables include pressure, temperature, flow and many other application criteria. Control valves are typically actuated either pneumatically, hydraulically or electrically. This means a control valve is connected to some sort of plant operating system, for remote operation and for plant operation signaling.

Pressure regulators are self-contained valve and actuator combinations that limit flow through a restricting element to match flow demand downstream. The desired performance of a regulator is to meet any downstream flow demand while maintaining a constant outlet pressure. Pressure regulators do not require any type of external actuation, which is where the self-contained portion of the definition comes into play. Unlike control valves, they operate solely by sensing pressure fluctuations and making corrective adjustments. This means they are usually limited to applications where pressure is the controlled variable.

Continue Reading

Flow Measurement Sustainability

Flow measurement systems require ongoing attention, especially in critical applications such as fiscal measurement and custody transfer.

Jason Laidlaw Oil & Gas Advisor, Emerson Flow Solutions

Jason Laidlaw
Oil & Gas Advisor, Emerson Flow Solutions

Sustaining-Flow-MeasurementIn a Scandinavian Oil-Gas magazine article, Sustaining Quality Flow Measurement in Critical Applications, Emerson’s Jason Laidlaw explains the need for good measurement repeatability and low uncertainty for oil & gas producers to meet their engineering assessment, review, and audit requirements.

He opens noting that flow measurement device repeatability is a building block for systems which have low uncertainty and accuracy when compared to a reference standard. Jason asks:

How do you ensure that same repeatability when it comes to the on-going review and assessment of the system?

More than technology is required. For these engineering assessments, review and audits:

…good repeatability and low uncertainty are the result of having trained, skilled and competent personnel. Good accuracy comes from having consistent reference sources such as a standard, best practice or technical guidance note.

Jason notes that the process itself adversely impacts the measurement over time. How much: Continue Reading

Wired Versus Wireless Risk Analysis for Process Instrumentation Measurements

How does wireless communications compare against wired communications for process instrumentation? That was the subject of an Emerson Exchange presentation by Kenexis’ Ed Marszal and Emerson’s Gary Hawkins. Their presentation, Risk analysis of wired versus wireless transmission of process measurements was recently narrated by Ed as an encore presentation and uploaded to YouTube.

In this 30:31 video, Emerson Exchange 2014 Wired V Wireless, he discusses the strengths and limitations of using wireless communications for both basic process control and safety. He presents a typical fault tree analysis comparing the communication types along with case studies where wireless communications have been used successfully. Continue Reading