Numerical and Experimental Investigation of Polymer-Induced Resistance to Flow in Reservoirs Undergoing a Chemical Flood

Abstract

Polymers are commonly used in chemical EOR flooding to provide mobility control to the injected fluid slugs. Water-soluble polymer injection in porous media usually results in polymer entrapment in the subsurface formation from adsorption, mechanical trapping, and hydrodynamic retention. These different entrapment mechanisms lead to permeability reduction (Rk). The term resistance factor (RF) is used to measure the impact of permeability reduction and viscosity enhancement from the polymer. The residual resistance factor (RRF) represents the residual permeability reduction to chase fluids (usually water) following a polymer flood. These phenomena are more prevalent in high molecular weight polymers. The effects of RRF are also sometimes evident when polymer injection is suspended (e.g., operational issues) and other fluids are injected in the formation instead. Post-polymer chase water injection is considered a viable option to improve economics of a polymer flood. Current models validate this optionality because they overestimate the efficiency of the chase water flood. Lab and field observations indicate that chase water after chemical flood can cause rapid breakthrough, and therefore it is generally not recommended. The shortfall lies in the assumption that permeability reduction during polymer flood is an irreversible mechanism and therefore the existing simulation models assume that the permeability reduction during and post-polymer flood is the same. In this work, we show that the permeability reduction mechanism can be somewhat reversible, and therefore the current models underestimate chase water injectivity, and more seriously can overestimate the efficiency of chase water displacement. For optimizing the slug size, over predicting chase water displacement efficiency has a critical impact on the project economics and it may wrongly indicate premature switching time from chemical to water injection. We provide an alternative permeability reduction model that does not assume irreversibility. The new model decouples permeability reduction during polymer flood from RRF during chase water flood. We validate the model using experimental data. Several test cases are provided to compare the two models and we finally demonstrate the applicability of the proposed model in an onshore polymer flood pilot. The new model also highlights the seriousness of the inefficiency of the post-polymer chase water injection.

Visualization of Polymer Retention Mechanisms in Porous Media Using Microfluidics

“…Other experimental results showed that even after 100 PV of injected chase water, permeability in the core was not restored entirely, which indicates partial reversibility (Seright 2016(Seright , 2017. Hoteit et al (2016) confirmed this behavior and emphasized that the typical models, adopted in reservoir simulators, that assume irreversibility are unrealistic, and typically overestimate the recovery factor from chase water, which could mislead the design of the polymer-flood slug size. Polymer retention is typically assessed indirectly from the pressure drop and effluent concentration profiles.…”

Investigating the Propagation of the Colloidal Dispersion Gel (CDG) in Thick Heterogeneous Reservoirs Using Numerical Simulation

“…Thus, polymer adsorption is the most important mechanism, which is defined as the adhesion of the polymer molecules onto the rock surfaces [43]. A recent study suggested that the permeability reduction caused by polymer flooding might not be the same after post-treatment water injection and the performance of the reservoir after the treatment might be exaggerated [44]. In addition, the permeability reduction caused by CDG injection could be removed with prolonged injection of chase water [9].…”

“…The results shown in Table 9 suggest that assuming irreversibility of polymer adsorption will give higher results compared to other options (i.e., partial reversible and reversible adsorption). To show if the permeability reduction caused by the gel treatment will vanish and be removed as concluded by other researchers [9,44], an extension of post-treatment water injection until year 2050 was considered (the default end date of the simulation run was 2020). shows that after prolonged injection of post-treatment water for the reversible adsorption model, there was still permeability reduction in the thief zone (layer 1) and the gel treatment was not removed completely.…”

Novel Approach to Model and Visualize the Transport of Polymer Molecules in Porous Media Using Microfluidics

“…Polymer-induced formation damage impacts the recovery performance and manifests as a continuous deterioration of well injectivity. (Seright, Seheult and Talashek, 2009;Glasbergen et al, 2015;Hoteit et al, 2016;Torrealba and Hoteit, 2019). The polymer-induced formation damage related to pore-throat clogging, or simply polymer clogging, is generated by the polymer entrapped in the pore space (Sugar, Torrealba, Buttner, & Hoteit, 2020).…”