Making High Quality Frac Water out of Oilfield Waste

Abstract

Fresh water and affordable energy are two of the most valuable resources on the planet for sustaining economic growth and development. As the demand for oil and gas continues to increase, the fresh water consumption rate by exploration and production (E&P) activities is skyrocketing. Competition for fresh water is threatening to become an industry-limiting factor in some oil and gas plays. To ensure that the fresh water needed by the oil and gas industry is available in the future, better water resource management practices must be developed and implemented.Currently, the drilling, completion, and stimulation of each horizontal shale well consumes up to 10 million gallons (gal) of fresh water, roughly equal to daily indoor water usage of 125,000 people [U.S. Department of the Interior March 2010]. Once fresh water becomes oilfield waste, the water is typically disposed of into reservoirs below the fresh water table, permanently removing it from the fresh water cycle. Reusing the water is desirable but often presents technical problems with water quality, water management logistics, and cost.To help address these problems, a Forward Osmosis (FO) water reclamation process has been adapted for the oil and gas industry. The first generation of the process reclaims drilling waste water by converting it into high quality base fluid for hydraulic fracturing. In contrast to other water treatment systems, like reverse osmosis and evaporation, FO is a unique nano-filtration technology that harnesses the potential energy in a brine water solution as the drive mechanism, thus making the technology extremely "green" and cost competitive. Unlike conventional filtration to remove solids, the FO membrane rejects all solids and virtually all solutes from the reclaimed water, thus yielding a nano-pure water that will not react adversely with fracturing chemicals or the reservoir.The results of laboratory and field testing from early commercial jobs show that FO is a viable technology for the reclamation of drilling waste for beneficial reuse as a high quality completion fluid. The results also show that FO can help significantly reduce both the carbon footprint and water footprint of the oil and gas industry.

Raising forward osmosis brine concentration efficiency through flow rate optimization

“…Thermally-regenerated FO has also been modeled by Semiat et al [17]. An FO pilot system with RO regeneration (FO-RO) was used to concentrate low-salinity O&G wastewater [2,18]. FO-RO has also been suggested to be more efficient than RO for seawater desalination [19,20], but other studies have shown that this is unlikely [21,22].…”

“…FO-RO has also been suggested to be more efficient than RO for seawater desalination [19,20], but other studies have shown that this is unlikely [21,22]. Another FO pilot plant forgoes draw regeneration in favor of "osmotic dilution" [2,18]: the dilution of a pure sodium chloride solution powers the concentration of O&G wastewater. Osmotic dilution is also used in emergency hydration [23], fertigation [24], and other applications described in [25].…”

“…4 and A.1 using data reported in Refs. [2,11,14,18,20,26,27,28]. Processes are represented with arrows that begin and end at the feed and concentrate salinities, respectively.…”

“…However, in the Hutchings et al pilot [18], at least 75 kg of NaCl must be consumed per cubic meter of water removed from the feed (see Appendix B), and the process produces saline water rather than fresh water. Draw solutes other than NaCl may be used, but in each case the cost of sourcing the solute and the cost of disposing (or value of producing) the dilute draw must be considered.…”

“…where. Figure 4 demonstrates the effect of balancing at a fixed terminal osmotic pressure difference (35 bar, based on the low-salinity FO-RO pilot [2,18]) using salinity profiles derived in Appendix C. As the mass flow rate ratio is varied, the slope of the draw salinity profile changes. Larger mass flow rate ratios lead to a smaller change in draw salinity but require that a larger mass flow rate goes through the regeneration device.…”