Phase behaviour of Maya crude oil based on calorimetry and rheometry

The phase behaviour of Maya crude oil and its nano-filtered sub fractions was studied using differential scanning calorimetry and phase angle measurements in the temperature range 173-573 K at atmospheric pressure. The combination of these two techniques elucidated key phase behaviours, i.e. temperatures and enthalpies of phase transitions and their nature. Based on this information a preliminary pseudo-binary temperature-composition phase diagram for Maya crude oil was constructed. As nano-filtration partitions samples on the basis of asphaltene content, within experimental error, the composition coordinates are maltenes and asphaltenes. Broad solid to liquid transitions are identified for both maltenes and asphaltenes individually and the phase diagram is dominated by 2 three-phase zones: solid maltene + liquid maltene + solid asphaltenes at low temperature, and liquid maltene + liquid asphaltene + solid asphaltene at higher temperature. This contribution also illustrates a phase diagram preparation approach with broad potential for application to reservoir fluids, heavy oils and bitumen where conventional approaches frequently cannot be applied. In addition, heat capacity data for Maya crude oil samples are reported in the temperature range 210-560 K.