Answering questions about Electrical & Industrial Process Tomographies
Published Feb 01 2020
Pekka Kaunisto

What is tomography?

Tomography is the technology that allows us to provide solutions that see inside pipes and separators/tanks, removing doubt from your multiphase flows to cut downtime and optimize your production.

The general idea in tomographic measurements is to expose the target of interest to a physical stimulus, e.g. electromagnetic waves, radiation beam, acoustic waves or electrical signals, and measure the response caused by the target. From the response signals it is possible, with the aid of mathematical models, to infer the distribution of different material within the target. Results of tomographic measurements are displayed as an online cross-sectional or 3D image of the target and indices.

One of process imaging solutions is based on a tomographic technology called Electrical Tomography (ET). The basic idea in Electrical Tomographic image construction is to find a permittivity/conductivity distribution for which the observations predicted by the model are in good agreement with actual ET measurement data. 


When tomography?

Electrical tomography can be easily deployed to solve problems other technologies are not suitable for, especially in a case of heterogeneous process conditions:

Rocsole's tomographic technology. Tomography practically means slice imaging (tomo = slice, graphy = images)


Why tomography in Oil & Gas?

Electrical Tomography (ET) enables whole volume imaging of a process pipe or separator/tank without using a radioactive source. Indices, such as a percentage of free volume in a pipeline with deposition growth, are calculated from the image.

One of the main advantages of the technology is that it can differentiate all the fluid (oil, gas, water) and solid (waxes, scales, hydrates, sand) phases inside pipelines and tanks—even when there is deposition present on the sensor. Using tomographic technology to address flow assurance challenges that have been previously unsolved, Oil & Gas operators can now see and monitor—in real-time—deposition and flow regimes inside pipes and interfaces and the emulsion layer inside separator tanks. From the image, one can crosscheck the accuracy of the indices. Other monitoring technologies—that do not have the benefit of the image—require a blind trust of the index alone.


Tomography versus Nuclear

While safety can be a concern, the cost of ownership is the most significant drawback to nuclear technology. Costs and associated challenges include:

  • Maintaining dedicated personnel to handle the device
  • Ongoing training of personnel
  • Meeting complex regulations related to shipping, transporting, handling and storing of the device


Tomography versus Pressure Loss Monitoring

An increasing loss of pressure in a pipeline due to increasingly constricted flow can be an indicator of solids deposition in the line. The use of pressure loss in a segment of pipeline, however, is poor indication of deposition. First, the loss of pressure, or pressure drop, in multiphase flow can be attributed to a number of causes, such as changes in flow regime, liquid viscosity, gas fraction, water fraction, etc., so an increase in pressure drop doesn’t necessarily point to flow constriction caused by solids. Second, in cases where there has been deposition, we repeatedly see there must be a substantial reduction in flow path cross-sectional area to give a significant pressure drop versus time signature. In essence, as a lagging indicator, monitoring pressure drop in a pipeline is not a very good method to detect solids deposition, except to warn of the final closure of the flow path.

Tomography's Improvement of Fluid Modeling

Modeling to predict solids appearance is widely practiced in some sectors of the industry, but is currently done without deposition measurement data. A fluid model is most often the best indicator—or only indicator—an operator has to predict deposition growth rate. Instrumented pigging or permanent pipe sensor measurement can provide key data to tune and improve models for more effective management strategies. The combination of measurement and modeling is better than either effort alone.


Deposition Watch

By monitoring deposition such as wax, scale and ashphaltenes in pipelines, you can:

  • Extend cleaning cycle and reduce production loss
  • Measure conductivity and permittivity in build-up conditions
  • Measure mass flow build-up conditions

Deposition Watch concept, by Rocsole

Flow Watch

Monitor flow regimes such as slugging, water breakthrough and homogeneity in pipelines in order to:

  • Optimize pipe flow conditions to manage slugging
  • Water cut and water holdup measurement in stratified conditions
  • See mixing efficiency
  • Optimize multiphase metering by seeing the flow regime

Full Flow Visualization Capabilities of Flow Watch, by Rocsole

Sand Watch Pipe Sensor

Quantify the actual percentage of sand in your pipeline while monitoring the sand layer in multiphase flow containing gas.

  • Measure solid levels in separators to optimize cleaning periods
  • Measure solid levels and mass flow in pipelines
  • Measure solid levels in sand processing units to optimize discharging periods

Before the installation of a profiler, the solid level cannot be seen. After installing the sensor, the solid layer is visible and provides real-time infromation of the growth speed of the layer, optimizing cleaning periods. By Rocsole

Emulsion Watch

By monitoring your separator tank's emulsion layer thickness and interfaces, you are now able to:

  • Improve separation efficiency by optimizing the emulsion
  • Avoid the cost of ownership associated with radioactive devices

Pekka Kaunisto
Electrical Tomography
Tomography in Oil & Gas
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