Abstract

In water injection operations, oil is displaced from the heterogeneous porous media that increases recovery factors while providing pressure support. The most important parameter to be considered in such water flooding operations is the mobility ratio. For increasing the mobility ratio to maximize volumetric sweep of injectants, gelling agents (polymers) are added to the injected water. Extreme temperature and shear stresses can result in the degradation of these polymers, i.e., long chain macromolecules of the polymer are split into smaller chains. Therefore, it is of utmost importance to select the right type and amount of these viscosity reducing agents for each reservoir.

In this paper, synthetic polymer mechanisms have been compared to a natural polymer (Xanthan), using a commercial full physics reservoir simulator. The assumption made in the simulation is simplified gel kinetics that forms a microgel without redox catalysis. The injection schedule is as follows; Continuous water injection over all 6 layers for first 450 days, gel system injection in the bottom two layers for the next 150 days and water injection is continued for 4 years. Reservoir model consists of a high permeability streak at the bottom of the reservoir while the top 4 layers have high horizontal permeabilities. The simulator is also coupled to an optimizer and an uncertainty analysis tool in which control and uncertainty variables are set to investigate the sensitivity under this process.

Simulated model results show that the gel penetrates deep within the reservoir model and the high permeability bottom layers are blocked. The relative merits of synthentic ploymers to natural polymers are obtained from the sensitivity studies. These suggest that Biopolymers and xanthan polymers have better performance in terms of viscosity effects whereas resistance factor and in-situ gelation treatments are highlighted for synthetic PAM. Adsorption and retention of polymer and gel are permeability dependent.

Given the potential for the application of polymers in reservoirs worldwide, this study compares and highlights the relative advantages of different treatments in terms of different parameters for the same model while showing the significance of each control and uncertainty variable. The economics of injecting different conformance enhancers have been analyzed as well in this study.

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