Shale Water and NORM
25 October 2019
- There are four types of shale waters, each with unique properties, uses, and treatment approaches.
- If your frac or produced water contains NORM (naturally occurring radioactive material), plan to manage them by keeping them in solution, precipitation and safe handling, or dilution followed by water disposal.
- Lithium extraction with petrolithium water only makes sense when concentrations are greater than 500 mg/L.
Shale water management starts with understanding the distinct types of water, their uses, and their volumes. This will enable better management of the site’s water balance to ensure there is the right amount of water available when needed and excess water does not exceed your storage capacity. Practitioners also need to consider the chemistry, which may include scalants, total dissolved solids (TDS), and NORM (naturally occurring radioactive material). The water chemistry significantly impacts shale produced water treatment strategy, as well as informing end-of-life options for the waste by-products that are left behind once clean water is removed. These by-products are often referred to as reject or residuals.
The Different Types of Waters Used in Shale Gas Operations
There are four primary types of water used in shale gas operations.
Source water is drawn from nearby water sources, such as surface waters or groundwater, and is typically used for hydraulic fracturing (also known as ‘fracking’).
Saline Re-Use Water is the water that returns after the fracking process, with increased salinity, but can sometimes be re-used as source water. It may require mild treatment before being used for another fracking process.
Frac Flowback is the water that returns from the ground, following a fracking process. Most of it returns rapidly after the fracking process and will include chemicals employed in fracking that can change the treatment process. The flowback flow rate slows over the first week(s) while TDS concentrations increases. Some of this flowback may become saline re-used water, if needed for future fracking applications.
Produced Water also returns to the surface, like flowback, but produced water largely originates in the formation. It tends to flow more steadily over longer periods of time and will have a higher TDS.
|Water Type||Utilization||Characteristics||Treatment||Volume (m3/day)|
|Source Water||Fracking||Usually locally sourced freshwater such as surface water or groundwater with little to now TDS.||Chemicals and sand enhancements may be added.||High during fracking process, then tapers to zero.|
|Saline Re-Used Water||Fracking (Re-Used)||TDS: 10,000 to 200,000 mg/L.
Scaling ions can be present.
|If re-used in a fracking process, it is often filtered and occasionally softened (remove Barium & Calcium).||Best maximized to reduce future management volumes.|
|Frac Flowback||Re-used if source water needed, otherwise disposed or treated.||TDS increases over the first week of flowback.||See our Shale water treatment options here.||High immediately post fracking (~70% of injected water returns), flow rate tapers down over the first week.|
|Produced Water||Re-used if source water needed, otherwise disposed or treated.||TDS varies but often as high as 100,000 to 200,000 mg/L.||See our Shale water treatment options here.||Ranges from 10-1000 m3/day (63-6,300 BBL/day) per well.|
- NORM: NORM are naturally occurring radioactive materials, with radium and its many forms being the most common. Not all produced water contains NORM, but they are occasionally encountered in North American shale. It is important to understand the major risks associated with handling water that contains NORM since these risks can be managed. First, ingestion of radioactive material either through inhalation or swallowing is the primary hazard. Always wear gloves and wash your hands and clothes whenever working around potentially radioactive material. Never eat food near NORM and do not bring gloves used to handle NORM into a food zone. Gamma rays given off by NORM are the second way they can be harmful – however, water is an effective insulator. Putting this into context, humans are exposed to more radiation on a 2-hour flight, than standing next to NORM containing produced water for an extended period.
- There can be some risk if NORM precipitate and become dried out, removing the insulating properties of water. NORM can be precipitated alongside barium, which can be achieved by adding sulfates (sodium sulfate) or carbonates (sodium carbonate) at an elevated pH (pH > 9). NORM may also precipitate as a sludge on the bottom of tanks and filter bags, and they should be checked with a radioactive test before handling for safe disposal by a certified party. Diluting NORM sludge with water can improve safety for the reasons mentioned above, however, this will create more liquid waste. The best strategy is to measure the presence of NORM in your water and develop a plan to manage them – either through precipitation removal and safe handling or water disposal.
- Chloride Dioxide Treatment and Removal: Chloride dioxide is used in shale waters to precipitate iron with possible NORM co-precipitation. As a benchmark, the cost of removing iron using chloride dioxide varies widely from $3-$50/m3 ($0.5-$8/BBL), depending on the volume of water that needs to be treated. Chlorine dioxide will damage membrane treatment systems, so if it is being used upstream of a membrane system be sure to remove it. There are many options for this, including activated carbon (expensive) or sulfites addition (more common).
Lithium: Some oil field brines contain lithium in the 60-100 mg/L range (0.006-0.01%) and there has been some emerging excitement for the potential of harvesting lithium from oil field brines. See an overview of lithium brine extraction technologies. Saltworks holds patents on lithium extraction, has built machines for lithium companies, and has technology to selectively extract lithium across ion exchange membranes. Saltworks has experience in this field, combined with an understanding of the costs and revenue potential. Extremely large volumes of water must be processed to harvest a meaningful mass of lithium, often pointing to a centralized system and transportation costs to reach that system. In the authors’ view, the best economics for produced water management are achieved through sound water management and treatment, rather than lithium extraction, however, this option can be reviewed if rich lithium brines are co-located with centralized high volumes of produced water.
Shale gas and oil production presents a leading energy source moving forward, yet its future and production is tightly linked to water management. Every water type, job site, and economic case is different. Contact us to review your specific situation, benefit from our expertise, and assess if your water management costs or risks can be lowered.