Produced-water management can be a burdensome task for any operator. Some estimates suggest water management is up to 25% of the expense of a well in its lifetime (Matthews 2018). It often requires trucking through populated areas and exposure of workers to hazardous chemicals, and it generates public suspicion. In some areas of the US, but not all, water disposal through injection is an expensive, ineffective method. In some US fields, disposal by injection is a limited option because of seismicity concerns or capacity issues. In keeping with the strengthened initiative of the Society of Petroleum Engineers to encourage sustainability, reuse options warrant an occasional viability review, even if produced-water disposal by injection is available and affordable.
Options for the reuse of produced water are becoming increasingly economic, available, and necessary. Reuse is driven by four factors: a more-open political climate that allows reuse, the need to restrict freshwater use, the prohibition or over-capacity issues of disposal by injection in some areas, and the advancing technologies available for both water treatment and possible reuse in completion fluids.
Periodic assessment of options for produced-water reuse is a valuable economic tool with sustainable-resource benefits. It is important to know what reuse options are available locally, what requirements must be met, and what quality of water is available in the field. These parameters are ever-changing, so periodic evaluation of reuse viability is a smarter option than permanent dismissal of a reuse idea.
To begin a viability assessment, it is important to start with an accounting of the entire life cycle, including resources used, material processed, transportation costs incurred, waste produced. Consider any possible products that can be derived. Be open to any new reuse ideas, and try to look for the potential benefit. Once an outline of potential reuse options is developed, the viability assessment can begin.
Step One: Evaluate the Waste Water
In order to evaluate the types of possible reuse, the wastewater characteristics must be determined (e.g., water volumes, physical water characteristics, and chemical water characteristics). Begin a sampling plan throughout the field. Collect samples of produced water from every type of source in the field (e.g., flowback, at the tanks, and at saltwater disposals). Ideally, the water should be collected after it has settled. Make sure to sample at multiple times throughout a well’s lifespan. The intention is to have a solid idea of wastewater patterns both chronologically throughout a well’s lifespan and geographically in the field. Make sure physical water characteristics (e.g., temperature and density) are collected in addition to chemical compositions. Laboratory results are an essential component to the success of a reuse program.
Determine accurate volume data from your wells. Compare multiple sources where volumes are reported [e.g., supervisory control and data acquisition (SCADA) tank level measurements, separator meters, water-hauling receipts, and injection receipts]. On occasion, the volumes reported by the water hauler are not as accurate as the measurements pulled from SCADA tank readings. Take the time to compare the two. Again, measure at multiple times during a well’s lifespan to develop predictive patterns as wells age. Seasonal trends also may become apparent after the data has been collected.
Step Two: Evaluate the Options
Review the water-quality results and determine a list of reuse options. Start with a list of what can be reused with minimum treatment (e.g., evaporation beds, crop or golf-course irrigation, dust control, watering for pad reclamation, rangeland restoration, and livestock watering).
If the water has contaminant concentrations that are too high, treatment will be required before reuse. This water usually has more-industrial applications (e.g., for cooling towers, pulp and paper mills, cement and concrete mixing, mining floods, and soluble-mineral extraction).
The production company will see the greatest economic benefit if the water can be reused directly on site (e.g., in drilling muds, hydraulic-fracturing fluids, heavy brine for workovers, enhanced-oil-recovery waterfloods or steamfloods, or soil cement for pad construction). The exact treatments required to reach a usable water quality will vary considerably, but start with settling and filtration. The water chemistry will dictate what further treatment is necessary.
When evaluating reuse options, do not disregard the water’s physical characteristics. Produced water with a sufficient density can have a viable reuse as heavy brine water once it has been disinfected properly. Additionally, produced water can come up hole at temperatures near boiling (200°F). This available energy can be used as heat during distillation or for field evaporation, steam production, or electric generation.
Do not forget to evaluate the physical inputs of the treatment technology. How will it be powered? Will it work remotely? What volumes can it handle? Is it robust? Will wells need to be shut in if something fails? Work through the diverse possibilities of actual operation in the field.
Step Three: Evaluate the Costs
Determining the costs for reuse is the most difficult part. Water volumes and chemistry will vary, and budgeting for these considerable variations is difficult. Start with the costs of freshwater sourcing. Water-supply costs often are a driving factor of a reuse/recycling plan. Research the costs of the current disposal plan, including treatment, transport, and storage. Are there any contractual minimum-volume requirements? Check with accounting to see how the freshwater-purchasing and wastewater-disposal fees are distributed among the lease and partners. Then, determine your company’s actual cost.
Two methods to help contain treatment costs are field managing the water quality and supervising the concentrations of the downhole chemistry used. After reviewing the results of the chemical-sampling program, manage your gathering system where there is one available “cleaner” source of produced water. Direct the gathering system or water haulers to load a selected tank facility with less-heavily-contaminated produced water to use as your source material for the reusable water. By starting with a lower-concentration source, the costs of treatment will be reduced. Also, manage the downhole paraffin thinners and descaling fluids so that they do not foul the “better” produced water. If sample results reveal exceptionally high levels of methanols (or other constituents of your downhole chemistry), reduce the rate or load. High-concentration results mean the chemical is coming back up unspent.
Step Four: Evaluate the Reality
Determining what wastewater-reuse options are physically possible and affordable is not the end of viability determination. The regulatory, environmental, and social effects also must be determined. Will the regulators buy in? Is this going to require a year-long permitting process? Does the treatment process use combustion to provide clean water? Will the process itself require an additional air permit? Will the limits of the air permit be achievable? (The National Ambient Air Quality Standards maximum lbm/hr restriction is a tough standard to meet for some sources of combustion). What other air, water, or waste issues will be generated? Will the reuse/recycling lead to measurable social effects (e.g., noise, traffic, or explosive atmospheres close to neighborhoods)?
Many more decisions must be made to refine the type of reuse possible for an operator, but this four-step process is a good start to determine what process warrants further scrutiny. Of course, economics is usually the basis of any reuse decision, but preparing a reuse-viability study in advance of a freshwater shortfall or a disposal issue can give operators an advantage when the time comes to react to change.
Additionally, as more reuse is put into place, expenses will begin to decrease because of the economies of scale. The Global Petroleum Research Institute reports that one-third of the produced water in Texas is less than 10,000 ppm total dissolved solids (Burnett 2018). That is a significant useable resource. Reuse of this resource can make economic sense with a sustainability-conscious benefit.
Laura Slansky is a certified hazardous materials manager and a certified safety manager. She can be reached at lhslansky@gmail.com.
References
Matthews, C. 2018. The Next Big Bet in Fracking: Water. Wall Street Journal, 22 August 2018, https://www.wsj.com/articles/the-next-big-bet-in-fracking-water-1534930200 (accessed 14 November 2018).
Burnett, D. 2018. Potential for Beneficial Use of Oil and Gas Produced Water, https://www.researchgate.net/publication/237345333_Potential_for_Beneficial_Use_of_Oil_and_Gas_Produced_Water (accessed 14 November 2018).