In the quest to put the puzzle pieces together to help convert the saltwater (brine) that is coproduced with gas and oil into a usable product, and help solve the problem of water shortages, polluted surface and ground water, and and a host of other issues, we are featuring interviews and technology profiles that relate to questions raised by our earlier post, Getting Started in Purifying Produced Saltwater, the Overlooked Resource in Resource Plays.
When visualizing how produced water could be purified and used in useful applications, a number of questions come to mind. I've listed a few of the ones that immediately occurred to me, and I asked Patrick Horner of Aqua-Pure (Fountain Quail in the U.S.), to respond to a few questions. Thank you, Patrick, for responding.
1. How easy is it to get started distilling water from a well that is making 100 bbls of fluid a day, with 5% oil cut and 50 mcf gas?
Typically, on-site distillation systems for volumes of 100 bb/day are not practical from a cost/logistical perspective. We would recommend a water management system (either pipeline collection system or truck pick-up) that brings water to a central facility capable of processing 4000 bbl/day. A separator could be used at the well to separate gas and/or oil. Oil could be kept with the water and separated at the central facility to minimize equipment at the well (gas/liquid separation equipment would be required at the well prior to transportation of the water).
2. Do you have to let the water settle longer? Do you recommend using surfactants to separate the water and oil more quickly?
This is very much a function of the nature of the oil (API density etc and degree of emulsification). The oil water separator can be designed accordingly (surfactants may assist in the separation process, again usually depending on the degree of emulsification). There are many effective de-oiling technologies available but again these can range from simple tank systems (gun barrel type) to hydro cyclone type separators depending on the amount and type of oil.
3. Can you use the produced gas as energy for the distillation / condensation process?
Yes, we currently use produced gas in our NOMADS to power the process. Some level of gas treatment many be required depending on the quality of the gas. Typically, for raw gas, this involves a coalescing type filter to remove any liquids and/or solids. If H2S is present, this would need to be scrubbed out.
4. How pure is the end product? Is it potable?
We have designed our systems to meet EPA NPDES discharge permit requirements (not potable water specifications).
5. Does distillation remove aromatic HC?
Distillation does not remove aromatic HC. Anything more volatile than water will carryover with the distillate (and MVR Evaporation). There are ways to ensure aromatic HC is not present in the distillate. This would include reducing aromatic HC prior to the evaporator (via oxidation and/or stripping) and polishing the distillate if required (oxidation and an adsorption bed such as activated carbon to polish). Biological methods can be used to remove organics from the distillate as well but this requires the addition of nutrients which may in the end reduce the overall water quality.
6. Do you get EPA Drinking Water approval at the wellsite, or should we take the water elsewhere for further processing / testing?
Again, a NPDES discharge permit is a realistic goal for this type of water treatment. We haven’t evaluated EPA Drinking Water approval. Any level of treatment is possible, it’s just a matter of what is feasible from a cost perspective. By meeting the NPDES requirements, I expect we are close to drinking water standards but the level of oversight/monitoring/testing/QC would likely be a step up for EPA drinking water standards. This may not be practical at small volume facilities. I expect that if the treatment facility meets EPA NPDES, the water could be transported to a drinking water treatment facility for further processing to meet EPA Drinking Water Approval.
In North America, there is big perception issue with where the water comes from. Singapore has a facility that recycles municipal sewage into drinking water (at a quality higher than we typically see in North America), even though they are meeting the requirements, the optics of where the water came from would be an issue in NA. I expect the same would be the same for turning oilfield produced water into drinking water. I’m not aware of any scenario where oilfield produced water is being turned into drinking water in North America I am aware of a few projects in Australia that are doing this but again (recharge drinking water aquifers with treated produced water), the culture is different. I’m curious if you know more about this.
(Susan's response: No, the only ones I can think of that might be similar are in Wyoming, where "fresh" water coproduced from coalbed methane is used to recharge surface impoundments (which would eventually recharge groundwater, and a few possible areas in Texas where produced water is used in lined stock tanks for personal use on private property.)