Many oil-producing basins were ancient ocean beds, once awash with sea creatures and salty water. For unconventional producers in these areas, getting a 5:1 to 10:1 water-oil ratio, dealing with oceans of water is a daily battle. The one thing that has indeed dried up is extra funding that would help deal with those water issues.
Even with the expansion of recycling for use in fracturing, the vast majority of produced water is injected into saltwater disposal (SWD) wells, which have been associated with man-made tremors and costs about $9/bbl when including transportation and disposal costs.
To deal with the flood of water and the drought in dollars, producers are increasingly open to new or reengineered methods of disposal. In that category, RWI Enhanced Evaporation has spent the last two years engineering and testing a new evaporation technology designed to make it much more cost-effective and more compliant with increasingly strict environmental regulations.
The main problems with previous evaporation technology were twofold. First, they allowed too many total dissolved solids (TDS) and total suspended solids (TSS), many of which are toxic, to disperse through the air, sometimes floating for hundreds of miles before settling. Second, they were inefficient, costing about $.20 cents/bbl. While this is less than the $9/bbl for SWD, evaporation leaves a certain amount of water that still needs to be disposed, so those barrels incur both the evaporation and disposal costs on the water that remains.
Older systems typically fractured water droplets to below 50 μ, which is the point at which their particulate matter becomes light enough to float into the air. Common pollutants include salts such as sodium chloride, sodium sulfate and calcium chloride, among others. By its nature, produced water is loaded with contaminants. In the Permian Basin, for example, TDS alone tests at 6,000 ppm to 10,000 ppm.
RWI began testing APEX and LS 2.0 in 2017. Instead of starting with existing evaporator designs, most of which were based on snowmaking equipment that assumed fresh clean water was being used, RWI began by studying the mechanics of evaporation and working backward from there.
In the field, APEX and LS 2.0 have shown to be 16% more effective at evaporation surface area than older systems while using 90% less power and keeping droplet size above the 75-μ threshold. At this larger size, particles fall back into the pond for retrieval and disposal. By using 5-hp fans instead of 40-hp pumps, RWI 2.0’s energy costs are about 0.006 cents/bbl instead of 0.20 cents.
The units float on the pond’s surface, further ensuring the particles fall back into the water.
RWI began testing these units in a drill cuttings retention pond in Hobbs, N.M. The region’s hot weather allowed the ponds’ water to hold extremely high TDS densities—as much as 230,000 ppm. This provided an especially apt opportunity to test the unit’s ability to limit the drift of salts. It passed the test successfully.
Another test, which became a permanent installation, was put into a mining operation in Washington. There, RWI placed 15 Landshark 2.0 evaporators (the landbased version of the floating unit). Total power draw for these units was 56 kWh, 88% less than the 450 kWh required for previous evaporation systems.
Especially in arid climates common to many oil basins, a significant amount of water evaporates with only the help of solar radiance, airflow across the water and water temperature. This is known as the “lake rate.” Many older evaporation systems actually worked to reduce the lake rate, which is one reason they were so inefficient. The RWI Series 2.0 is designed to work with this free evaporation instead of against it.
The spray nozzles in 2.0 are designed to inject into the middle of the water stream, which reduces droplet collisions that cause the droplets to break apart into daughter particles that are smaller than 50 μ. These smaller particles are the ones that dry out in flight and allowed the ion contamination in the water drift into the air as a dry aerosol. In many cases, physical evidence can be seen in colored salt deposits and corrosion on adjoining fences, buildings and grounds, rendering those areas almost unusable.
Meeting EPA regulations
More stringent air quality regulations released by the U.S. EPA in 2018 (e.g., Rule 40 CFR 51-300) have made noncompliance, inherent in older methods, in danger of fines or even well shutdowns. Its key phrase for evaporation is as follows: “Visibility impairment that is caused by the emission of air pollutants from numerous sources located over a wide geographic area.”
This visibility impairment is a result of particles and gases in the atmosphere that scatter and absorb light, thus acting to reduce overall visibility. The primary cause of atmospheric haze is light extinction (scattering and absorption) by particulate matter. This visible pollution common in snowmaker-based evaporation units also is eliminated by Series 2.0 units.
In addition to air quality improvements, this unit reduces the amount of SWD injections by about 90%, cutting injection costs by that amount.
After the evaporation process, the TDS and TSS concentrations for the water now to be injected are much higher, raising questions about its injectability. In researching this question, RWI discovered that TDS levels up to 160,000 ppm can be safely injected without damaging the formation that receives the water.
APEX and LS 2.0 can be used either by larger E&P firms with in-house water plants or by SWD companies to reduce costs and extend the life of their injection wells.
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