No abstract

N2 and CO2 assisted steam huff-n-puff method has been proposed as the primary strategy to develop a new heavy oil reservoir located in the northeast of China having average oil viscosity of 5000mPa·s, reservoir pressure of 14MPa and temperature of 56°C. Prior to field application, a laboratory study from phase behavior to numerical simulation was conducted in this work. The experimental data showed that the swelling of the heavy oil as a result of CO2 dissolution varied almost linearly with pressure, but appeared independent on N2 pressure. CO2 markedly outperformed N2 in swelling heavy oil reducing viscosity and extracting hydrocarbon. In huff-n-puff simulation, averagely 4% and 6% of additional heavy oil was produced by steam injection compared to CO2 and N2 injection after natural depletion. In the scenario of gas assisted steam process, a more noticeable incremental oil recovery (>10%) was produced, which thus demonstrated its potential in this reservoir. The mechanisms of oil recovery stimulation were further elucidated using numerical simulation from the point of parameter variations for pressure, viscosity, temperature, and oil saturation.

Partially hydrolyzed polyacrylamides (HPAMs) are the most widely used polymers in enhanced oil recovery (EOR). This study presents capillary flow measurements of three different molecular weight HPAMs in synthetic brine. Polymer solutions having similar viscoelasticity were forced to flow through a 0.23 mm (radius) stainless steel capillary to investigate their flow characteristics including mobility reduction (apparent viscosity) and mechanical stability, represented by the extent of mechanical degradation (DR). The results indicated that the apparent viscosity of the polymer solutions markedly dropped with increasing flow rate until 5 mL/min, corresponding to the shear rate of 8,730s ¡1 ; after that a slight viscosity decrease was observed. The highmolecular-weight HPAMs (6.5 and 8.0 £ 10 6 g/mol) began to have slightly greater apparent viscosity than the low-molecular-weight HPAM (1.0£10 6 g/mol) above the shear rate of 26,180 s ¡1 ; this might result from the occurrence of the coil-stretch transition. All the HPAMs experienced very similar percentages of mechanical degradation (10%) at shear rates between 1750 and 8730 s ¡1 ; however, above 8730s ¡1 the high-molecular-weight HPAMs exhibited a steep increase in mechanical degradation (DR). On the other hand, in the case of the low-molecular-weight HPAM, the DR curve almost leveled off at 12%. Therefore, low-molecular-weight HPAMs are generally suggested for EOR applications. These results, we suggested, should be useful to improve the efficiency of polymer EOR by minimizing mechanical degradation.