Optimising polymer flood injection methods for EOR in heterogeneous reservoirs
Engineering Honours Degree 2008
University of Adelaide
This study investigated the benefits and challenges of implementing a successful polymer flood. Enhanced oil recovery techniques are becoming more important in the current scenario of high oil prices and the cost of a new discovery. Polymer flooding is a technique for unlocking bypassed oil in heterogeneous reservoirs by diverting the flood from high permeability thief zones. It can also mobilise heavy oil by modifying the viscosity of a water flood to improve mobility.
A literature review showed that polymer flooding can be very successful both economically and technically (De Bons and Braun, 1995), although there have been many unsuccessful projects in the past (Manning et al., 1983). Polymer flooding design involves several challenges not present in water floods. The rheological behaviour of polymer solutions is complex, and varies with temperature, brine salinity, polymer concentration and interactions with reservoir fluids and rock (Needham and Doe, 1987). Polymers can degrade at high temperatures, in the presence of oxygen and some chemical impurities, and under mechanical shear (Chang, 1978). Laboratory testing and pilot operations can minimise risk of reservoir incompatibility. Common failure modes include not injecting enough polymer, as results may not be observed for several years (Lake, 1989), and underestimating the injectivity pressure requirements of the viscous polymer solution (Jennings et al., 1971). Most of the technical and economic challenges can be overcome with appropriate management and planning (Kaminsky et al., 2007).
Reservoir simulation studies were conducted on a simple three-layered model to evaluate polymer flooding against water flooding. Polymer flooding was found to have a modest 4% increase in ultimate oil recovery than a water flood. Polymer flooding also delayed water breakthrough, with up to 35% increase in production to breakthrough. The study also showed that polymer flooding is most successful as a secondary flood (an enhanced water flood), rather than following a traditional water flood. A tertiary polymer flood will still improve reservoir sweep and increase ultimate recovery.
A parametric sensitivity study showed that the most sensitive inputs were the polymer solution viscosity, polymer amount and concentration. These values can each be optimised during the design process. Other inputs such as polymer adsorption, residual resistance factor and inaccessible pore volume did not impact on the parametric study but are significant as they are representative of the specific properties of the polymer and the reservoir.
Polymer flooding is receiving renewed interest in the industry following several very successful large-scale operations over the last two decades and increasing attractiveness of EOR to monetise oil resources that are already discovered and proven resources. Polymer flooding is now a proven technology that, with effective design and management, can be a successful and cost-effective way to improve oil recovery.