Development of a capillary rheometer for the characterization of heavy and extra-heavy oils
Viscosity and flow behavior of crude oils are key properties for the characterization, management and development of petroleum reservoirs. To measure the rheological properties of heavy crude oils with a high accuracy, a capillary rheometer was designed and built at the Ruhr-University in Bochum (RUB), Germany. The capillary rheometer was calibrated with three Newtonian reference blends of 1000 mPaBLs, 10000 mPaBLs and 50000 mPaBLs. For these standards the viscosity tables have been extended up to 1000 bar in the temperature range of 20 to 120 °C. The extended viscosity data was determined with a falling body viscometer at the Universidad Nacional Autónoma de México (UNAM), obtaining average deviations better than 2.0 % at high pressure. The capillary rheometer is then calibrated with the same reference fluids at 40, 60, 80 and 100 °C at pressures from 1 to 260 bar. The deviation from the reference value was found to be lower than 3 % at high pressure. The flow behavior of a heavy oil sample is determined at 80, 100 and 120 °C at atmospheric pressure. Furthermore, the viscosity is measured from atmospheric pressure to 180 bar. The investigated heavy oil shows a Newtonian behavior at high temperatures. This is consistent with rheological measurement carried out at UNAM. The viscosity increases with increasing pressure at all temperatures. For example, at 40 °C the viscosity increases by about 35 % by increasing the pressure from 1 to 100 bar.