This editorial originally appeared in the October 2019 issue of iWWD as "Measuring Refinery Water with Mag Meters"
The magnetic flow meter has rarely been considered a critical technology in upstream oil and gas, but the recent rise in produced water as part of oil production in the U.S. has created new opportunities for it.
Magnetic flow meters, or mag meters, often are used in municipal and industrial water and wastewater management, but their ability to handle corrosive mixtures is proving to be reliable and robust enough to meet the demands of the oil production industry.
In some of the more unconventional oil plays in the U.S. where oil is produced, it is estimated that for every barrel of oil pumped from the ground, four barrels of water also are produced. To effectively measure and manage that water is important in meeting reporting requirements, particularly environmental regulations such as those from the U.S. EPA.
Traditionally, turbine meters were used for produced water applications, but they often are unreliable, with moving parts that are subject to corrosion and wear, and they tend to drift over time, thereby reducing accuracy.
Operating on Faraday’s law of electromagnetism, the mag meter has no moving parts and instead uses sensors to pick up the level of magnetism in the flow going through the meter. The sensors relay that information to a transmitter, and the data from the transmitter is what a technician then uses to determine flow.
It is important to ensure pipe leading into and out of the meter are not magnetic, so the material does not interfere with accurate measurement. That said, a mag meter only needs a small section of straight run pipe upstream and downstream to properly function.
While mag meters are not traditionally considered a good fit for the hydrocarbon industry, they are becoming the meter of choice in slurry-type applications where water is involved. With built-in tools like meter verification software, a facility can use this technology to generate all the data needed to more easily meet reporting requirements.
Injecting Water or Pumping it Out
Whether injecting water mixtures as part of the hydraulic fracturing (fracking) process or managing the associated water that is produced with the oil, the measurement of the water content is important for several reasons, including:
Determining the quality of the separation process;
Understanding the potential corrosivity and salinity of the water impacting pipes and equipment; and
Maintaining the correct mixture of sand and water slurry during the injecting process.
While there are some new developments in oil separation that use freezing or an onsite hydrocyclone, the primary method of separating water out of oil today is by heating the mixture. No matter which process is used, oil separation requires significant investment of time and money, and knowing the amount of water to remove can make the process more efficient.
Corrosivity and salinity of the water is dependent on whatever particles, chemicals or bacteria are present in the water, and each can impact the longevity of the equipment the water comes into contact. In addition, saline water is bound by strict environmental rules in terms of how it can be used.
For example, if the salinity is too high, it may be unsuitable for irrigation purposes, and it may need to be processed before any further application is sought.
Slurry mixture that is injected into the well as part of the hydraulic process is a mixture of, primarily, sand and water. That mixture, however, needs to be accurate or it can clog or damage systems, which ultimately reduces efficiency.
Effectively Managing Produced Water
The wastewater that is a byproduct of oil drilling can be treated in several ways, similar to municipal and industrial water treatment methods that are subject to strict EPA regulations.
Most often, the produced water goes through a process to clean it for reuse or re-inject it into conventional wells. It first is fed into separators to remove the oil and then is transferred into holding tanks before being sent to a wastewater disposal/treatment facility either offsite or onsite at the same place the oil is brought up.
The water then is subjected to a combination of filtration, evaporation and chemical treatment to remove debris, harmful chemicals/salts and bacteria. Depending on salinity levels, the water may be stored in saltwater disposal wells.
At many points along this process, accurate measurements are essential, from knowing the amount of water that is moving through the system, to having insight into the purity of the water or being able to accurately determine the amount of chemical cleaning agents to add.
There also is a cost associated with sending water to offsite treatment facilities, in which case accurate custody transfer is important for accurate accounting and record keeping.
Measurement Challenges of Produced Water
One challenging aspect of measuring produced water is the presence of sand, salt crystals, oil and other materials that can introduce noise and inaccuracies into the measurement. For turbine meters, this would often mean corrosion and wear of the turbine blades and bearings, ultimately leading to drift and eventual failure.
These particles typically cause minimal damage to full-bore magnetic flow meters, as they have no moving parts, making them ideally suited to handle these challenges. Additionally, advanced signal processing routines and the ability to migrate to different coil drive frequencies can provide a means to stabilize the flow signal, allowing for real-time, accurate measurement of the produced water.
This helps lead to better water management practices and better well optimization. Optional diagnostics may also provide greater insight into the process by leveraging data along with pre-configured algorithms in the control system to roughly estimate solids or oil content.
The value of these measurements lies in analyzing the mixture being produced and how best to process it from there. Is there residual oil in the mix that needs to be further processed? Is the salinity of the produced water too high for any other immediate uses, requiring further clean up? Answering those questions quickly ensures an optimized process.
As monitoring and measuring produced water becomes more and more critical in oilfield applications, magnetic flow meters are gaining more consideration as a potential solution.
From the ability to deal with various water contaminants such as sand, salts and oil, to providing an accurate measurement suitable for custody transfer to water disposal companies, to simplifying environmental compliance mandated by local, state and federal governments, magnetic flow meters are demonstrating they can be an ideal choice to meet produced water management needs.