Oil and water may not mix, but in the oilfield, they do mingle. When a barrel of oil is produced, a certain amount of water, 5 bbl perhaps, comes gurgling out of the ground, too. The goal of new research and technologies is to find a suitable destination for that produced water.
The University of Texas Permian Basin’s Texas Water and Energy Institute (TWEI) is studying methods to treat produced water an repurpose it for construction sites, to irrigate crops, support power generation, potentially recharge aquifers or add to surface water.
The TWEI has two research projects underway and has already developed a database that companies can consult to determine whether their technology is capable of treating produced water from certain locations.
TWEI director and dean of the College of Engineering George Nnanna said the institute aims to find ways to use renewable energy-based sources to treat produced water and to increase water intelligence through data analytics.
The oil and gas industry produces lots of water, but it must first be treated before it can be reused if operators don’t reinject it into the original reservoir. Different uses of the water have different treatment requirements.
In the Permian Basin, total dissolved solids can reach 200,000 mg/liter, which makes treatment challenging.
“Eventually, if it’s well-treated, I think it might not be far off to recharge the aquifer,” Nnanna said. “In the California area, where the produced water has low dissolved salt, they are discharging it into the surface water.”
Nanoparticle floating system
One of the efforts underway at TWEI is a floating membrane system. The porous membrane design features nano-sized particles, and it floats on the surface of the produced water tank.
When the water permeates through the membrane, it evaporates. The clean water vapor is then collected and condensed into purified water.
Nnanna said the membrane enhances evaporation, which “we have been perfecting.”
The process, which Nnanna calls Enhanced Evaporation using Solar Umbrella, has “worked perfectly” in the lab and has tested well at the pilot scale. It has drawn industry interest, and TWEI has been working toward an additional pilot at life scale for the past six months.
During that pilot, TWEI gathered and analyzed data that will help determine the parameters that affect the membrane’s performance.
The lab test, which lasted a few weeks, generated a 17% to 20% enhancement in the evaporation rate, Nnanna said.
“We have ongoing experiments,” he said. “We are still getting temperature, humidity and other data.”
The material for the membrane is inexpensive, so the economics should not make treatment cost-prohibitive, he said. The membrane has been continuously used for six weeks without performance degradation issues.
Skimming the surface
TWEI is also researching the viability of a pre-treatment system that injects tiny air bubbles into the bottom of produced water tanks. As the bubbles rise through the water, they can pull particulates to the surface of the water for skimming.
Following the initial pre-treatment, chemicals could be added to the water to help particulates coagulate before running the produced water through a series of filters to “produce a much cleaner water,” Nnanna said.
TWEI has a 1,900-sq-ft facility to house the dissolved air floatation system. The next step for the research is to have the industry test produced water for effectiveness.
TWEI has built a produced water database using more than 23 million data points collected from the U.S. Geological Survey across 45 different industries.
Nnanna said the data is being analyzed for the potential to make projections about the behavior of produced water in the future. The database is available from TWEI and is accessible via subscription. A group within TWEI maintains the database.
“With our database, you can look at the water chemistry in a certain location and make a judgment if your technology is capable of treating the produced water from that place,” he said. “Instead of going to the field to test it, you can look at this database, and it will give you an indication of the range of total dissolved solids.”
The database has also made it possible to establish an empirical correlation between total dissolved salts and sodium and chloride.
“Instead of doing a laboratory characterization of produced water to get information on the total dissolved solids, if you know the concentration of sodium and chloride, you can use this equation to establish what the total dissolved solids will be,” Nnanna said.
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