The Atmos book of pipeline simulation - chapter 11

Offline and online simulators: the digital twins

Investing in a strong, underlying physical pipeline model for offline studies pays dividends during a pipeline’s lifetime. Further value can be added when an underlying model for offline studies is adapted for deployment live on site, in an online environment. The online simulator acts as a digital twin for the pipeline and keeps smarter operations flexible, safe and profitable through the use of features such as:

• Auxiliary software which validates incoming raw data and displays calculated results and alarms
• Automatic learning of parameters to keep the model well-tuned
• Virtual meters, inventory calculators and other features like leak detectors to inform operators about the current state of the pipeline system

Deploying an online simulator to a live environment is a process that demands fast-solving and seamless performance at all times, but simulation software like Atmos SIM is able to create accurate models while keeping them as simple as possible.

But how does it monitor a pipeline network in real-time?

Here we will discuss the following considerations of an online simulator that enable it to monitor a pipeline network live on site:

• Fluid type
• Communicating with the user
• Data processing
• Metering and instrumentation

Fluid type

An incompressible model is best suited for most applications involving pipelines carrying liquids, provided the liquid isn’t drastically compressible or multiphase. The incompressible model keeps track of batches as they move through the pipeline system and it doesn’t attempt to deduce flow rate, but instead follows a fiscal meter. Its batch tracker is in a continuous state of improvement because whenever a batch is detected passing by a mid-line station or arriving at its destination, corrections are made to the relevant parameters.

The real-time transient model (RTTM) is used on other liquid pipelines and all gas pipelines. RTTMs provide visibility and insight into what is happening throughout the pipeline network at all times, including the physical conditions at unmetered locations. The RTTM evaluates measurements against calculated flows and pressures and a state estimator uses learnt tuning corrections to maintain the model’s agreement with valid measurements.

You can read more about real-time transient models in our blog summarizing chapter ten of “The Atmos book of pipeline simulation”.

Communicating with the user

Previously it was only simulation specialists conducting offline studies and day-to-day pipeline operators relying on a modern pipeline simulator, but simulation software now has the facility to interact with a greater range of pipelining team members, adding value to a pipeline’s many technical and commercial tasks.

Integrating a pipeline simulator with a SCADA system enables a user-friendly display of information to everyone who needs it. Control room and office users can utilize this information to combine real-time data at virtual meters across the pipeline with predictive look-aheads and the historical logs.

Once a simulator deduces what’s happening in the pipeline, the auxiliary software suite interfaces with the end user. Because an operations team consists of several different roles, there might be different interests when it comes to live and historical information and reports. The system often involves communication back to the simulator, affecting interventions and corrections. A single console may manage many pipelines so a human-machine interface (HMI) can be used to monitor pipelines in real-time as effectively as possible.

The HMI is a set of screens and views that keep an operator informed, in control and are typically tailored for the pipeline operation team’s needs while complying with stringent standards.

Data processing

A pipeline simulation system only performs as effectively as the operations team behind it. The purpose of a pipeline simulator is to provide information, so the onus is on the end user to use the insights.

Simulation software is often robust enough to require minimal intervention in service when it’s commissioned by a capable team supported by developers. Simulated results can deliver impressive accuracy when the system is set up adequately and receives validated data. After being cold-started, a healthy simulation suite can be expected to align with reality and provide real-time support effectively.

SCADA system

It’s common for pipelines to use a supervisory control and data acquisition system called SCADA system. This centralized system sits between the simulator and field instruments, data historians and operator screens, allowing users to respond in real-time. It involves many operational technologies and gathers data from remote devices, making it available at a single centralized location.

Figure 3: A SCADA screen’s view of a pumping station along a pipeline

A SCADA system handles raw data, covering every variable about the pipeline’s ongoing operation, such as:

• Conditions at metering stations
• Valve positions
• Pig launch events

In the event that incoming information is inconsistent, it’s essential to help a simulator make sense of conflicting information through maintenance, which is an important task for a team on a project or maintaining a commissioned system.

How a system is set up, tailored for a unique site and monitored during an operation will determine how well it performs in real-time. Atmos can provide Maintenance support for this.

Metering and instrumentation

Virtual meters

Even pipelines with a steady flow will likely have certain locations in the pipeline networks where operating limits could be violated because of the terrain. Atmos SIM monitors these areas using reporting points which act as virtual meters, providing pipeline operators with the same information a meter would even though there’s no physical meter in this area. For a live simulation, reporting points provide the needed coverage of remote unmetered sections in a pipeline network and they also inform design decisions during offline studies.

Pressure meters

Part of ensuring a pipeline has the most appropriate instrumentation to monitor in real-time requires installing co-located pressure meters. Co-located pressure meters are commonly located on either side of a valve in case a valve closes and on both sides of a regulator, pump or compressor, that way when a valve is open or a compressor is off then the pair of pressure meters are measuring the same pressure as one another.

Flow meters

Strict standards of accuracy are demanded on a gas pipeline because of the custody transfer that takes place live on site. Failure to achieve this stringent level of accuracy even by one percent in the gas flow can amount to millions in losses to a seller or purchaser, so an equation of state is used with a pressure and temperature measurement to calculate billed flow from measured flow.

On a liquid pipeline, fiscal metering is also essential and Atmos SIM’s real-time incompressible model takes it over any flow rate indicated by pressure meters. Stringent requirements in both gas and liquid pipelines make flow meters an expensive addition to a pipeline network.

Preparing for online simulator success

A multitude of problems can occur on-site in any live environment, such as weighing up flow meters against pressure meters, the transition from a state far from real conditions to a state that matches real conditions and how to persevere through data flaws. A substantial amount of work goes into ensuring a real-time simulator circumvents these problems and pipeline networks are at less risk overall when they have an online model in place.

References

¹ “The Atmos Book of Pipeline Simulation”

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