The adoption of a common water quality guideline could help drive down costs and improve efficiencies for produced water recycling.
Adopting a common spec for recycled produced water would allow the industry to move toward larger-scale water recycling systems which are necessary in order to bring down operating costs and ultimately raise recycling rates. This was the argument made by XRI Holdings senior vice-president of business development Aaron Horn in a presentation and panel discussion at the Produced Water Society’s 2020 Seminar.
Horn’s proposed guideline is called SpOT Check and includes a pH spec in the range of 6-8, oxidation reduction potential (ORP) of at least 250 mV and turbidity at less than 25 nephelometric turbidity units (NTU). It also requires that salinity at any level be reported for the design of a suitable hydraulic fracturing chemistry. Iron content is not specifically considered under the SpOT Check as it can be inferred through other metrics: the higher the ORP and lower the turbidity, the lower the presence of iron.
One obstacle to raising reuse is lack of scale, in part due to the high variability of produced water quality and the specs that operators request. Horn said it may be possible to get the industry to coalesce around a common water spec at the point of sale, noting that there was already some consolidation around turbidity, iron and ORP specs in 14 requests for proposals issued by different operators in 2019 (see chart).
KEY PERFORMANCE INDICATORS FROM PRODUCER RFPS (2019)
| Turbidity (NTU) | Iron (mg/L) | Oil (mg/L) | Oxidation reduction potential (mV) | pH range | |
| 10 | 1 | 5 | 150 | 5.0 | 8.0 |
| 20 | 2 | 5 | 150 | 5.5 | 7.5 |
| 20 | 2 | 5 | 200 | 6.0 | 8.0 |
| 20 | 5 | 10 | 200 | 6.0 | 7.5 |
| 20 | 5 | 40 | 250 | 6.0 | 9.0 |
| 25 | 5 | 50 | 250 | 6.0 | 8.0 |
| 25 | 5 | 50 | 300 | 6.0 | 8.0 |
| 30 | 5 | 100 | 350 | 6.5 | 7.5 |
| 30 | 5 | | | 6.5 | 7.5 |
| 30 | 10 | | | 7.0 | 7.5 |
| 30 | 10 | | | | |
| 50 | 10 | | | | |
| 100 | 10 | | | | |
| | 10 | | | | |
NB: There were also five instances of a request for non-detect for hydrogen sulfide gas.NB: Bold cells indicate producer consolidation around water quality specs Source: Aaron Horn, PWS Seminar 2020 presentation
According to Horn, a common spec would remove some of the roadblocks in the wider adoption of infrastructure networks, similar to what XRI has established in the Permian Basin. The company has two commercial Water Exchange Terminals through which it gathers produced water from multiple clients, then treats and pipes it back to producers in different locations for oilfield reuse.
Large-scale systems such as these will be necessary as recycling rates rise. Multi-client recycling becomes attractive at 30,000 bbl/d, and the economics are further improved when considering 100,000-bbl/d systems, Horn told the audience. Moving in this direction would reduce producers’ operating costs, which are a key factor in water management decisions such as whether or not to recycle.
Horn estimated that the share of water sourced from recycled volumes stands somewhere in the range of 15-50%. “I’d say that at least three quarters of the folks out there would readily recycle if the economics made sense in their area,” he said. “I think we’ve probably reached a ceiling until we start to pull together multiple parties and aggregate water at a scale that drives down the water management cost.”