Environmental Risk Management of Produced Water - A Demonstration of the CHARM Model Used for the Ula Field in the North Sea

Abstract The Blane field is a sub-sea oil and gas production development located in the southern part of the North Sea straddling the UK and Norwegian border. The field is expected to produce inorganic scale (BaSO4) when injection water containing sulphate breaks through in the production wells. This will require scale inhibitor squeezes from an intervention vessel to mitigate scale deposition. The wells were completed with long horizontal sections straddling multiple producing zones. This could potentially result in scale deposition severely reducing productivity if both formation water and injection water were to be produced simultaneously into the wells. Adding to the complexity, the perforation guns were left in the wellbore as part of the completion preventing any access to the perforation area. The distribution of scale inhibitor during a squeeze pumping operation could therefore be uneven leaving parts of the well poorly protected. In addition, the guns prevent physical removal of any type of materials in the well bore like asphaltenes, sand and scale which could plug off the perforations during a pumping operation with a well intervention tool; Wireline, coiled tubing, etc.. Injection water supplied from a host platform is used for pressure support of the reservoir. During the field development, the injection water was expected to contain mostly produced water reducing the scale potential considerably as it would have low sulphate content. When water injection started, very little produced water was being produced resulting in mostly seawater being available available for pressure support. Scale deposition in the well and around the well bore could therefore prove to be impossible to control unless reactions in the reservoir would reduce the scale potential or a reliable scale inhibitor squeeze method to mitigate scaling could be identified. This paper describes the joint effort of 6 different companies to identify the risks associated with the inorganic scaling during production and how a scale squeeze strategy was developed. The work included scale inhibitor selection, a geo-chemical study, and reservoir and near well bore simulations, sub-sea deployment selection, deciding on water chemistry and production monitoring and development of an overall management plan.

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Membrane separation of produced water

Water Science & Technology ◽

10.2166/wst.1996.0221 ◽

1996 ◽

Vol 34 (9) ◽

pp. 239-246 ◽

Cited By ~ 21

Author(s):

T. Bilstad ◽

E. Espedal

Keyword(s):

North Sea ◽

Suspended Solids ◽

Produced Water ◽

Synergistic Effects ◽

Membrane Surface ◽

Volume Reduction ◽

Chemical Cleaning ◽

The North ◽

Environmental Controls ◽

The North Sea

Each time regulatory agencies initiate more stringent environmental controls, treatment technologies are refined to meet the updated standards. Centrifuges and hydrocyclones are, by and large, producing satisfactory effluents for meeting current quality requirements for the offshore petroleum industries. The European standard for effluent from onshore petroleum activities, however, requires less than 5 mg/l total hydrocarbons (HC) and less than 10 mg/l suspended solids. Such low concentrations are out of reach for the above classical separation processes. The amount of produced water in the North Sea is projected to increase by a factor of 6 from 1990 to the year 2000; from 16 to 90 million cubic meters each year. Produced water is the predominant source for oil discharges. The synergistic effects of chemicals, oil and dissolved components in the produced water effluent are given increased attention, with expectations of tougher effluent criteria. Microfiltration (MF) and ultrafiltration (UF) pilot trials with produced water from the Snorre field in the North Sea showed that UF, but not MF, could meet more stringent effluent standards for total HC, suspended solids and dissolved constituents. Total HC in the produced water was typically 50 mg/l and was reduced to 2 mg/l in the UF permeate (96% removal). The aromatics benzene, toluene and xylene (BTX) were similarly reduced by 54% and the heavy metals copper (Cu) and zinc (Zn) by 95%. UF trials were performed with organic tubular membranes with typical transmembrane pressures between 6 and 10 bars. The feed velocities through the tubes were between 2 and 4 m/s. Flux varied from 140 to 550 l/m2/h (lmh) at a produced water temperature of 60°C and membrane molecular weight cut-off between 100,000 and 200,000 daltons. By recirculating UF retentate as membrane feed, a volume reduction (VR) of 24 was obtained in the trials; i.e., 96% permeate recovery. The limited volume of produced water available in the feed tank negated further volume reduction. Full-scale design is based on permeate recovery of 99%. No irreversible fouling of the membrane surface was experienced. The cleanwater flux was restored after chemical cleaning. The alkaline detergent Ultrasil 11 was chosen as the optimal cleaning agent.

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