fax 01-972-952-9435. AbstractProduction of extra heavy oil or bitumen by means of SAGD (Steam Assisted Gravity Drainage) requires the generation and injection into the reservoir of a great quantity of steam. A corresponding quantity of hot water is then produced along with the mobilised oil. Bearing in mind existing and future environmental regulations, it is likely that partial or even total recycling of this produced water back into steam will become mandatory. The complexity of the water treatment scheme required depends on the water characteristics, the steam boiler specification (OTSG or conventional 100% steam boiler) and whether or not waste water disposal is completely eliminated (zero reject) or not. SAGD developments have some specific water treatment issues which need to be addressed, for example the high silica content of the produced water. This paper will present different conceptual designs for a 300 000 bwpd water treatment plant. The different schemes discussed include an OTSG boiler, a conventional boiler and the zero disposal option. The various options available for process equipment will be presented, together with two different salinities of produced water and their impact on process design. Included will be an evaluation of capital cost and operating costs elements.

The production of extra heavy oil (or bitumen) through the SAGD method (Steam Assisted Gravity Drainage) requires the generation and injection into the reservoir of a great quantity of steam. A typical value of the steam/oil ratio is around 3, which means that a 100,000 bopd development requires the injection of 300,000 bcwepd (barrels of cold water equivalent per day) of steam, and that a corresponding quantity of hot water will be co- produced with the oil. The production of extra heavy oil containing many active components with the tendency to form an emulsion combined with the high water-cut ratio (above 80%) leads to a phase separation process with specific issues. This study considers an extra heavy oil field produced in SAGD in Athabasca. The objective of the study was firstly to characterise the produced fluids and then to analyse their tendency to form an emulsion under controlled hydrodynamic conditions. An innovative technique - Differential Scanning Calorimeter (DSC) - was used to characterise the emulsion. This method is able to define the water-in-oil or reverse emulsion nature and to quantify the water amount without sample dilution. DSC analysis combined with microscopy and image analysis treatments was used to determine the droplet size distribution. Reconstituted emulsions were then formed using a "Dispersion Rig" set-up that allows the simultaneous pumping of crude oil and water through a calibrated restriction in the pipe. The amount of energy dissipated to the fluids systems can be quantified due to the strict control of the hydrodynamic conditions. Consequently a relationship between granulometry distribution of the emulsion and the fixed energy or pressure drop can be established. The main experimental parameters investigated were the oil dilution and water-cut ratios. It is concluded that there is a residual emulsion in extra heavy oil which has a very small average droplet size whatever the temperature and solvent dilution ratio. This small droplet size results in a difficult oil/water separation which is only possible either by addition of large quantities of additives at high temperature and with long residence time and probably by applying an electrostatic field. Introduction Albertan oil sand deposits contain an estimated 1.7 trillion barrels of oil of which 300 billion barrels are believed to be recoverable by surface mining or insitu developments. One of the insitu technologies which is used in several Athabascan developments is Steam Assisted Gravity Drainage (SAGD), this extraction technique injects steam continually adding energy and heating the reservoir. This injection produces a steam chamber within the reservoir enabling Extra Heavy Oil to be produced together with hot water back to surface via a production well. SAGD requires substantial quantities of steam. A typical steam/oil ratio is in the order of 3 barrels of water equivalent of steam per barrel of bitumen produced. This steam is then co produced in a multiphase mixture with the bitumen. This multiphase mixture must be separated to provide a dehydrated oil stream which may be transported for further downstream processing or upgraded on site. This water and oil mixture contains active components that promote emulsion formation. This tendency to form emulsions coupled to the produced fluids high water cut makes separation difficult to achieve. So that that this separation system can be adequately specified it is essential that the emulsion is characterized. This paper sets out the techniques used to characterise an Athabascan oil field emulsion, the equipment used to form the emulsion in the laboratory and then discusses the results of this characterisation. This paper sets out a methodology used to characterize and study the behaviour of emulsion produced from an Athabascan SAGD development.

fax 01-972-952-9435. AbstractThe production of extra heavy oil (or bitumen) through the SAGD method (Steam Assisted Gravity Drainage) requires the generation and injection into the reservoir of a great quantity of steam. A typical value of the steam/oil ratio is around 3, which means that a 100,000 bopd development requires the injection of 300,000 bcwepd (barrels of cold water equivalent per day) of steam, and that a corresponding quantity of hot water will be co-produced with the oil. The production of extra heavy oil containing many active components with the tendency to form an emulsion combined with the high water-cut ratio (above 80%) leads to a phase separation process with specific issues. This study considers an extra heavy oil field produced in SAGD in Athabasca.The objective of the study was firstly to characterise the produced fluids and then to analyse their tendency to form an emulsion under controlled hydrodynamic conditions. An innovative technique -Differential Scanning Calorimeter (DSC) -was used to characterise the emulsion. This method is able to define the water-in-oil or reverse emulsion nature and to quantify the water amount without sample dilution. DSC analysis combined with microscopy and image analysis treatments was used to determine the droplet size distribution. Reconstituted emulsions were then formed using a "Dispersion Rig" set-up that allows the simultaneous pumping of crude oil and water through a calibrated restriction in the pipe. The amount of energy dissipated to the fluids systems can be quantified due to the strict control of the hydrodynamic conditions. Consequently a relationship between granulometry distribution of the emulsion and the fixed energy or pressure drop can be established. The main experimental parameters investigated were the oil dilution and water-cut ratios.It is concluded that there is a residual emulsion in extra heavy oil which has a very small average droplet size whatever the temperature and solvent dilution ratio. This small droplet size results in a difficult oil/water separation which is only possible either by addition of large quantities of additives at high temperature and with long residence time and probably by applying an electrostatic field.

Summary The production of extra-heavy oil or bitumen using the steam-assisted-gravity-drainage (SAGD) method entails the generation and injection of a large quantity of steam into the reservoir. A similar quantity of hot water is produced together with the oil. Taking into consideration environmental regulations, it is probable that partial, or even total, recycling of the produced water into steam will be required. After circulating in the ground, production water may contain high concentrations of silica (up to 400 mg/L). Silica removal is very expensive in terms of investment and operating costs. The risk of silica-salt deposition in the boiler tubes becomes significant when the silica content in the feedwater exceeds 100 mg/L [once-through-steam-generation (OTSG) boiler-supplier specifications]. Deposition of silica increases local thermal resistance and can lead to tube failure. The silica-removal process is also an environmental issue owing to the production of sludge. This paper demonstrates that silica-scale inhibitors can be used in steam generation in an OTSG boiler. The original laboratory test program and results obtained are presented. Test results were corroborated on an industrial OTSG boiler in operating conditions. Results show that use of silica-scale inhibitors instead of silica removal could generate substantial savings in cost. The use of silica scale for steam generation in heavy oil exploitation has been incorporated into French patent 2,858,314-A1 (Gauthier et al. 2003). Introduction Typical steam/oil ratio values for the production of extra-heavy oil or bitumen using the SAGD method are between 2 and 4. This implies that the production of 1 bbl of bitumen requires the injection of 2 to 4 B/D of cold water equivalent of steam and that a similar quantity of hot water is produced together with the oil. In view of environmental regulations, it is likely that a partial or even total recycling of such produced water into steam will be required. Most boilers used in enhanced oil production with steam injection are gas-powered OTSG boilers. These were specially developed for thermal flooding applications and are commonly used because they offer several advantages over utility boilers: OTSGs require less maintenance and can tolerate fairly hard water with a relatively high content in (soluble) solids, monovalent cations, anions, and silica, because only 80% of the feedwater is vaporized in a single pass. The vaporization rate is directly related to the acceptable concentration of silica in the water. The risk of silica-salt deposition in the boiler tubes is high when the silica content in the feedwater exceeds 100 mg/L (OTSG specifications). Silica deposits increase the local thermal resistance and can lead to tube failure. Boiler-tube replacement resulting from silica plugging is costly. In SAGD operations, production water (after circulating in the ground) contains high concentrations of silica (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 U.S. $ 0.7/bbl) and 30% of the investment costs. Silica removal also generates environmental problems because of the production of sludge (120 kg of sludge for 1 thousand BWPD). Use of silica-scale inhibitors as a replacement for silica removal could result in substantial savings in costs. Six inhibitors, never used before in the petroleum industry, were developed and tested for that purpose.

No abstract