University of Ibadan, Department of Petroleum Engineering, Ibadan, Oyo-State, Nigeria.
The behaviour of emulsions stabilised by asphaltenes and six types of reservoir fines (montmorillonite, bentonite, calcite, siltstone, shale and sandstone) is described for systems in which the crude oil type is varied and for model oil containing hexane/toluene mixtures.
Several experimental techniques were utilized, and partly developed, for this study. A Soxhlet extractor was used to extract asphaltenes from oil sands bitumen, and a wet sieve analysis was developed to obtain micron sized solid particles. The stability of emulsions was assessed from the amount of water resolved after sedimentation and periodic centrifugation of the emulsions. In addition, a PTI-58 digital conductivity meter with Pt/Pt black electrodes was used to determine the emulsion type and also monitor the rate of demulsification.
Using conductivity measurements on the emulsions stabilised by solid particles, we deduce that catastrophic inversion from w/o to o/w was achieved for emulsions of hextol (a mixture of Hexane and Toluene) and water on increasing the volume fraction of water, φw, and occurs at 0.40 for sandstone and 0.60 for bentonite and montmorrilonite while inversion does not occur for Forcados Yorkri (FY) and Bonny Light (BL). This shows that the type and nature of emulsion can be expected to depend on the nature of the particles and organic phase.
The stability of the model, BL, FY emulsions increased as the asphaltene content increased to 3.2kg/m3, 3.8kg/m3 and 4.3kg/m3 respectively and decreased above these concentrations. Addition of solid particles to deasphaltenized and model oil samples had no significant effect on emulsion stability. However, in the presence of asphaltenes, emulsion stability increased as the particle size of reservoir fines decreased from 63microns to 0.45microns.
In conclusion, stable emulsions are formed with treated and model oil, whose stability depends on the nature and concentration of asphaltenes, the type and size of reservoir fines.
Bonny Light, Forcados Yorkri, Emulsions, Asphaltenes Bentonite, Montmorillonite, Calcite, Sandstone
