Choose the Right Instrumentation For Your Oil and Water Separator

Instrumentation provides you with sufficient information to make data-driven decisions in a safe and efficient manner and increase productivity through automation. The challenge is often to choose the right technology and features. This article will help you determine the correct type of instrumentation, suitable to your needs.

As this article is one of the more extensive ones we have published here at the Process System Performance blog, we have for your convenience, highlighted its content here:

1.Where to Start: Define Your Challenges

2.What Are Your Options?

3.Correlation Between Complex Fluids & Choice of Instrumentation

4.Long-term Value

5.Conclusion

Where to Start: Define Your Challenge

Instrumentation for your oil and water separator is a tool that helps solve specific challenges. As such, in order to choose the correct instrumentation, you have to begin by clearly identifying the challenges you aim to solve.

Take for example a diesel tank on a truck. The diesel tank can also be considered an oil and gas application, as diesel is a hydrocarbon. However, the diesel within the tank has already been processed and stabilised; meaning that there are no gas, water or emulsion present. As a result, there is no need for advanced equipment. The only thing you require is a levelmonitoring system that tells you when the diesel tank is empty, too full, etc.

Within the oil and gas industry there are several different latitudes – stages to the process; upstream, midstream, downstream, distribution etc.The instrumentation you need, thus vary on the stage.Consequently, if you have a simple application, you can look at more cost-competitive, simplified instrumentation packages.

Suggested reading: Instrumentation for oil and water separators: Just a cost or a great investment?

In the upstream stage of oil production, the fluid is unprocessed; meaning you have to deal with a lot of different, as well as uneven levels of fluids and solids. In addition, you could face more complex challenges such as high temperature and high pressure. Not knowing what is going on inside your separator can drastically reduce the efficiency of whole separation process as well as generating safety issues that could have huge consequences, such as explosions.

Hence, having instrumentation that allows you to make data-driven decisions, is als a matter of safety, not only efficiency and productivity.In short, if you are dealing with complex conditions, you require more data, resulting in more advanced instrumentation.

To help you make the right decision and optimize you separator performance, we will briefly outline the main two categories of level instrumentation in upstream production. Note, that there is a third category consisting of less advanced technology (like Ultrasonic and Non Contact Radar), but these are rarely used for upstream production today.

Category 1 - MostAdvanced. Able to read all layers, within the 3-phase separator such as water, oil, emulsion, foam and gas.

Nucleonic type of level instruments

• Uses gamma rays to measure fluids densities and then calculating the levels.
• Can be used for different measurements principles; continuous level measurement (full absorption), interface level measurement and to create a density profile of the emulsion layer.
• It is often used in situations where other simpler instrumentation cannot be used. This is typically in high pressure and temperature conditions, or if the fluids are very corrosive or extremely adhesive.
• Are you looking for the most exact information about the oil/water emulsion layer within the separator when using nucleonic instrumentation, density profiling will give you that.>
• This solution is a multi-detector solution where several detectors are installed on the separator wall or inside the vessel tank.

Capacitance type of instruments

• Uses a capacitor to measure the level of fluids within a separator.
• Capacitance technology is preferred in presence of complex fluids, when the crude oil is heavier and more viscous, as this introduces much more complex layers and less defined levels in production separators.
• Capacitance technology is more suitable than other measuring technology to deal with tight emulsions, long settling times and severe foaming.
• Has a fast response time which makes it ideal for separation processes with small separator tanks and where the levels are changing faster.
• Capacitance instrumentation is suitable in these “aggressive fluids” if you use a probe built in a prope resistant material.
• The advance capacitance level profiler technology can also provide a high level of resolution / visibility of the fluid layers inside the vessels.

Want to learn more about Advanced Capacitance? Check out this video!

Category 2 - Medium Advanced: The ability to read levels of oil, water and gas, but with limitations to measuring emulsion and foam.

Displacers (Buoyancy)

• Uses Archimedes’ Principle to determine the liquid level inside the separator.
• A displacer will function within a wide range of temperatures and pressures. However, the level readings available can be incorrect if the temperature and density of the liquid within the separator differs from that of the liquid found in the external cage.
• Suitable for interface level measuring if the specific gravity differs significantly (gravity difference greater than 0.1) and if the change in specific gravity caused by temperature or composition does not affect the results.
• Should not be considered as the measuring instrumentation for liquid levels when the fluid contains solid particles. This also applies to dirty, foaming, fouling service as well as turbulent fluid.
• Displacers do not work well in liquid-liquid interfaces where there is a potential of emulsion, as this will cause inaccurate measurements

Guided Wave Radar (GWR)

• Based on the Time Domain Reflectometry principle
• You can choose guided wave radar when the interface you are measuring consists of clean liquid-liquid interface and/or clean liquid-gas interface and clan liquid/gas interface
• The main limitation of this technology is that it is not a suitable measuring instrumentation if you are dealing with complex fluids, like emulsion, foam, fluid build-up or crystallization, as these conditions will like cause false readings.
• Changes in pressure, temperature, and most vapor space conditions have no impact on the accuracy of the level measurements.
• No need to compensate for changes in dielectric, conductivity, or density of the fluid.

Hybrid Capacitance/GWR

• Based on a hybrid technology between capacitance and guided wave radar.
• If you struggle with emulsion when operating with a guided wave technology to measure interface levels in your separator, choosing the hybrid technology can be an option to solve this problem.
• Hybrid capacitance/GWR have the same limitations as mentioned for both guided wave radar and capacitance technology

Magnetic Level Indicators

• A simple, rugged instrument that measures level or interface based on the effects one magnet has on nearby magnets.
• Can be used to measure interface levels given that specific gravities differ significantly. However, this only applies if the change in specific gravity due to composition or temperature does not affect the readings received.
• You should not choose to use magnetic level indicators if there is turbulent, dirty, foaming, fouling service or if the liquid contains solid particles like sand.
• You should not use magnetic level indicators to measure liquid-liquid interfaces when emulsions greater than a few centimetres are formed, or if the interface is not clean.
• Neither should you use the technology for liquid-gaseous services if the fluid specific gravity of at least one layer is not relatively constant.

Suggested reading: How To Build Your Oil & Water Separator for Long-Term Productivity

Correlation Between Complex Fluids Choice of Instrumentation

By looking at the brief description of the two main categories above, you can see that the presence of complex fluids is the biggest differential. In other words, when there is no issue with fluid complexity, there are several types of instrumentation technologies that can read the interface between two very different liquids (such as oil and water), or between two very different fluid phases like liquid and gas quite well.

The challenge occurs when the interface is not even and consists of a mix of several different fluids, thus creating uncertainties that can easily develop into issues. Solving these issues can take time, and consequently you are left with delays, reduced or loss of production and increased production costs. As such, when dealing with complicated mixes of fluids, you require an advanced technology that provides you with high quality data, allowing you to read, as well as understand the structure of the layers, and their behaviour over time

Long-term value

In addition to identifying your current problem, I recommend that you consider the changes that are happening within the industry. In other words, take into account not only what you need today, but what you might need further down the road.

Today, there seems to be a natural tendency to choose advanced instrumentation also for simpler applications, as it is viewed as a good investment; preparing you for the challenges you might face in the future. In addition, advanced instrumentation will provide you with more data for your digital twin and to feed with higher quality data your automation system. As everybody is focusing on automation and digital solutions to boost productivity, the quantity and quality of the data has become fundamental.

Oilfields naturally experience changes throughout their lifespans. Such as changes to the well stream in terms of flow rate, temperature, pressure, density, fluid composition and higher presence of by-products like water and sand, etc.

In other words, you may not need the most advanced instrumentation today, but it is likely that you will need it in a few of years. Advanced instrumentation can therefore make you more robust long-term and consequently make you a stronger competitor.

Conclusion

The simplest instrumentation is of course cheaper, however provides little information with little value. In contrast, the more advanced instrumentation creates more value over time and has a much higher degree of flexibility. Consequently, can be used for the whole life of the field.