Evaluation of starch based biopolymers for improved oil recovery

Abstract

Permeability variations, viscous fingering, and the resultant early breakthrough of injected fluids and the control of water production are common problems in Enhanced Oil Recovery (EOR) and/or production operations. These problems need to be studied thoroughly in order to optimize potential oil recovery. Polymers have been extensively used to solve these problems for several decades. However, technical and economical constraints in addition to environmental concerns make their use unattractive. Starch based biopolymers are suggested as an alternative for profile and mobility control applications. This study analyzes permeability modification due to polymer adsorption at the pore level and the effect of polymer adsorption on capillary pressure characteristics of reservoir rocks. Experiments are performed to determine the permeability reduction and the effect of polymer adsorption on capillary pressure curves, pore entrance size distribution, and the relative permeability curves. Environmental Scanning Electron Microscopy (ESEM) is used to study profile modification at the pore level. Visual correlation of ESEM images with the capillary pressure characteristics show that starch based biopolymers are very effective for profile modification. Therefore, these polymers can be used to recover additional oil where channeling and bypassing of oil by water are the main problems. A model is also developed to estimate the amount of polymer adsorbed in the porous media. The difference in pore size distribution before and after polymer treatment indicates the degree of effectiveness of the polymer to modify the permeability profile. The difference in capillary pressure curves before and after polymer treatment indicates the extent of polymer adsorption in the porous media. Due to their hydrophilic nature coupled with retention and adsorption, the starch based biopolymers cause a significant reduction in water relative permeability. Adsorbed polymer tends to reduce both wetting and non-wetting phase relative permeabilities in both sandstones for a concentration of 1.0%. The marked reduction in water relative permeability due to the hydrophilic nature of the starch based biopolymer, as demonstrated in this study, indicates that they should be useful in blocking water in production wells and plugging thief zones in injection wells.