Joel Minier-Matar

Assessing the Biotreatability of Produced Water From a Qatari Gas Field

Reuse of significant quantities of produced water (PW) extracted during gasfield operations requires treatment to remove both organic and inorganic materials. Biological treatment is generally regarded as the most cost-effective method for organics removal. For industrial waste waters, biotreatment faces distinct challenges because the PW composition can dramatically affect sludge settleability, a critical parameter in the operation of conventional biotreatment systems. Membrane bioreactors (MBRs) have an inherent advantage and have proved to be successful in the treatment of industrial waste waters because a membrane filter is used to separate the treated water from the sludge rather than separation being contingent on biomass settleability. The outcomes of a bench-scale experimental study on the application of an MBR to the biotreatment of PW from Qatari gas fields are presented for three operating parameters: hydraulicretention time of 16 to 32 hours, solids-residence time of 60 to 120 days, and temperature of 22 to 38 C. The impact on chemical-oxygen-demand (COD) removal was evaluated through experimental testing by use of three parallel bench-scale MBRs. Low sludge concentrations (0.3–1.5 g/L of volatile suspended solids) were attained throughout, with instantaneous-flux values ranging from 3 to 15 L/(m h). Results indicated that the COD removal averaged 60% (54–63%), approximately one-third of this value being attributed to physical removal, with the operating parameter values shown to have no statistically significant effect on removal. Although trends were consistent with some previously reported studies performed on refinery waste water, overall removals were lower than expected. The pH of the bioreactor sludge ranged from 4.9 to 6.0, averaging 5.2, compared with a feedwater pH of 4.3, possibly contributing to the low carbon removal recorded. Adjustment of the feed pH to more than 6.5 caused a precipitate to form that contributed to membrane fouling. However, all feedwater acetate and more than 90% of the oil and grease were removed by the MBR treatment. Treatment appeared to be carbon-limited, accounting both for the absence of nitrification (with all removed organic nitrogen apparently being assimilated into the sludge) and for the low sludge-solids concentrations attained. Evidence suggests the feedwater contains a significant fraction (approximately 40%) of highly recalcitrant organic compounds presumed to be nitrogencontaining field chemicals (e.g., scale inhibitors and corrosion inhibitors).

Treatment of Produced Water from Unconventional Resources by Membrane Distillation

Unconventional resources (Shale gas/oil) use significant volumes of water for hydraulic fracturing (fracking). While some of the water used is fresh groundwater, there are more environmental pressures to use brackish water sources for fracking. This brackish water may need to be treated to lower the saturation levels and to allow mixing of field chemicals. Unconventional resources also produced high volume of flow-back water (produced water). This produced water (PW) contains high levels of total dissolved solids (TDS) and desalination may be needed to allow recycling or reuse of this water source. Membrane Distillation (MD) is an innovative process that can desalinate highly saline waters (30,000–100,000 mg/L TDS) more effectively than reverse osmosis. As a proof of concept, bench-scale MD testing were performed on brackish and produced water samples (30,000 mg/L-60,000 mg/L TDS) obtained from Texas. Results have shown excellent TDS rejection (99.9 %) on all the water samples that were tested without impacting membrane’s flux performance. To evaluate the O&M and scale up issues, two one m3/day MD pilot units are currently operating side by side at a local desalination plant in Doha. Brine from the thermal desalination plant was used as representative high salinity water (70,000 mg/L), similar salinity levels could be found in brackish groundwater and/or flow-back water. It was assumed that all other contaminants that could cause membrane fouling (such as suspended oil, solids, organics, microorganisms) will be removed in a pretreatment step prior to MD. Preliminary results showed that the pilot units were successful in completely removing salt. Flux was very stable for more than 2 weeks. However, it was concluded that pretreatment is critical for stable performance of the MD units. This presentation will provide up to date data on MD bench and pilot-scale performance with O&M issues and projected cost estimates.

Advanced Technologies For Produced Water Treatment And Reuse

Produced Water (PW) is the highest volume liquid waste stream generated by the petroleum industry. Historically, the treatment of PW has been limited to free oil and suspended solids removal, using physical separation technologies, and injection in disposal wells. However, because of new regulations combined with geological restrictions and local water scarcity, the drive to have a greater fraction of the PW more extensively treated and ultimately reused is increasing. Moreover, the growth in the application of water intensive processes to extract unconventional oil&gas resources, in particular in shale plays and oil sands, has increased the need for cost-effective treatment and reuse of PW to reduce fresh water uptakes. Therefore, the petroleum industry is investigating new PW treatment technologies given that the physical separation technologies traditionally used in the past are, in most cases, not capable of producing water of suitable quality to replace fresh water uptakes. This paper presents the results of a laboratory investigation carried out by the ConocoPhillips Global Water Sustainability Center (GWSC), where various treatment processes (membrane processes, membrane-bioreactors (MBRs), membrane distillation (MD) and ozonation) were evaluated as treatment methods for PW from different oil&gas fields. The key conclusions of this paper are: • Membrane Processes and Thermal Evaporators are currently operating within the petroleum industry in full scale PW treatment and reuse applications. • The preliminary results of investigations performed by GWSC confirmed the potential of Membrane Filtration, MBRs and Ozonation to treat PW and produce an effluent suitable for reuse. Membrane Distillation may have potential in the longer term. Further investigation is ongoing. • If successfully implemented, the above technologies will contribute to provide the petroleum industry with a broad range of technologies to cost-effectively treat and reuse PW.

Application of Forward Osmosis to Reduce Produced Water Injection Volumes

Abstract One of the key challenges facing the gas industry in Qatar is to reduce produced water (PW) volumes injected in disposal wells by a target of 50% to ensure long term reservoir sustainability. This paper describes a novel adaptation of FO technology that could meet this target. In contrast with conventional FO designs, this adaptation uses readily available seawater or thermal brine as the draw solution and then, instead of recovering water from draw solution, simply discharges the diluted draw solution to the Arabian Gulf. This eliminates entirely the expensive and technically challenging draw solution recovery step. Produced water, in this paper, refers to a combination of produced water extracted from the ground and process water from on-shore operations.