Near- Wellbore Rheology of Alkali Surfactant Polymers
Research output: Thesis › Master's Thesis › Research
Polymer solutions are injected into oil reservoirs to increase the efficiency of water flood operations due to better mobility control and decreasing residual oil saturation. In the Vienna Basin in Austria a polymer injection pilot has been running since No-vember 2011. During injection pressure rises until the formation parting pressure is reached. Associated high shear strains acting in the polymer cause severe mechanical degradation. To quantify the rheological behaviour of polymer solutions mixed with alkaline agents or surfactants, core flood experiments and rheometer measurements were conducted within the framework of this thesis. To imitate the conditions of the pilot injecting into the 8th Torton Horizon of the Matzen reservoir, hydrolyzed polyacrylamide (HPAM) was used. Nordhorn sandstone was chosen to come as close to the actual reservoir rocks as possible. The average permeability of core plugs was about 2 Darcy and porosity about 25 %. Apparent viscosities were calculated from pressure differentials measured on the core plugs assuming a capillary tube bundle model. At velocities as high as in the near wellbore region of injectors, shear degradation was seen for all solutions tested. Addition of > 2 wt. % surfactant lead to up to about 20% higher apparent viscosities than inferred for the polymer-only solution but shear degradation still occurred A solution containing 10 wt. % Na2HCO3 was, however, found to show a much lower apparent viscosity than the reference solution without alkalis. At low velocities (1m/d), as observed in the depth of the reservoir, shear thinning behaviour was also seen for surfactant polymer solutions. Inertial effects were experimentally found to cause an apparent increase of brine viscosity of around 10%. This corresponds reasonably well to the analytic result that centrifugal forces reach a magnitude of about 7.9% of the viscous forces. Residual resistance factors RRF were also analyzed by comparing pressure profiles of brine floods before and after the polymer flood. It was found that RRFs increase with water flood velocity, rather than decrease. A clear trend among the different solutions tested was not observed. RRFs measured range between 2- 3.5. Viscosity data from rheometer measurements indicated pure shear thinning behaviour for all solutions. A correlation between rheometer- & core flood data was not found.
|Award date||19 Dec 2014|
|State||Published - 2014|