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.