A New Water Treatment Scheme for Thermal Development: The SIBE Process
- Pierre Pedenaud (TOTAL S.A.) | Fabrice Dang (TOTAL)
- Document ID
- Society of Petroleum Engineers
- International Thermal Operations and Heavy Oil Symposium, 20-23 October, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2008. SPE/PS/CHOA International Thermal Operations and Heavy Oil Symposium
- 6.5.3 Waste Management, 4.1.2 Separation and Treating, 5.4.6 Thermal Methods, 5.3.9 Steam Assisted Gravity Drainage, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.3.4 Scale, 4.1.5 Processing Equipment
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The production of extra heavy oil or bitumen through Thermal methods (e.g. SAGD - Steam Assisted Gravity Drainage) requires the generation and injection into the reservoir of significant quantities of steam which is finally recirculed with the produced bitumen. Considering the need to minimize fresh water consumption and the possibility of increasingly stringent environmental regulations, it is likely that maximization of the recycling of the produced water into steam will be mandatory.
The SAGD water treatment scheme is complex because it depends on the water characteristics, the steam generator type selected (OTSG or conventional boiler) and the decision to completely eliminate waste water disposal (zero liquid reject) or use other waste handling and disposal methods. SAGD water treatment also faces some additional specific challenges compared with oil fields worldwide, such as the high silica content in the produced water.
An overview of the current water treatment process options for SAGD will be presented, followed by a new patented process called SIBE (ie Silica Inhibition and Blowdown Evaporation). The principle of this new process is based on TOTAL's research in the area of silica inhibition and an optimized application of conventional water treatment equipment with Zero Liquid Discharge process (e.g. evaporators and Crystalliazer). An estimate of the economic benefit of the new SIBE process relative to conventional process schemes will be presented.
The steam/oil ratio for the production of extra heavy oil or bitumen via SAGD is typically between 2 and 4 bcwepd/bopd during the production plateau, i.e. one barrel of bitumen requires the injection of 2 to 4 bcwepd (barrels of cold water equivalent per day) of steam, the majority of this steam returns to surface together with the oil as hot water. Environmental regulations are likely to require that this produced water has to be partial or even totally recycled.
In Athabasca, most boilers used in enhanced oil production with steam injection are gas-powered Once Through Steam Generation (OTSG) boilers. These were specially developed for thermal flooding applications and are commonly used as they offer several advantages over conventional drum boilers (100% quality steam): OTSGs require less maintenance and can tolerate fairly hard water with a relatively high content in (soluble) solids, monovalent cations, anions, and silica, as only 80 per cent of the feed water is vaporized in a single pass.
Especially for Silica, the boiler evaporization rate is directly related to concentration of silica in the water because of the silica salt deposition risk in the boiler tubes (silica concentration specification below 100 mg/l for OTSG). Silica deposits increase the local thermal resistance and can lead to the tube failure. Boiler tube replacement due to silica plugging is costly. In SAGD operations, production water, after circulating in the ground, contains high concentrations of silica (experience shows concentration up to 400 mg/l). Silica removal is expensive owing to the consumption of chemicals. Its cost represents 80% of water treatment costs (which represent 0.7 $/bbl) and 30% of the investment costs. Silica removal also generates environmental problems due to the production of sludge (approx. 120 kg of sludge for 1 kbwpd). For OTSG boiler feed water
treatment, the use of silica scale inhibitors can replace silica removal units (eg WLS, HLS,…). and an optimized process of Zero Liquid Discharge OTSG boiler water treatment (e.g. evaporators, crystallizer and ion exchange units) could result in substantial savings in costs.
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