(376ba) Simulation Study of Macromolecules Propagation Mechanism in Heterogeneous Porous Media

With literature review and simulation study, we found that current polymer flooding model in commercial software cannot fully reflect the inaccessible pore volume (IPV) effect on conformance control. The objective of this paper is to review the concept and mechanism of inaccessible pore volume and correlate the current simulation model in commercial software based on experimental fitted functions.

METHODS PROCEDURES:

The correlated model is based on a comprehensive review of the lab experiments. Distribution of polymer molecules are related to the pore size. Saturation and porosity of polymer component have been specified based on inaccessible value of the grid considered. Core scale numerical simulation integrated with fractional flow has been used to investigate sensitivity of IPV to polymer flooding concentration distribution, velocity and residual resistance factor.

RESULTS, OBSERVATIONS and CONCLUSIONS:

Inaccessible pore volume has been a key influencing factor for successful conformance control in petroleum industry since 1970s. With reported, IPV values are very inconsistent and range from 0 to 48% of pore volume. As a result, optimization of IPV can additionally improve sweep efficiency of polymer flooding, which would result in a more favored polymer flooding efficiency. Ignoring the effect of IPV on concentration and retention can result in inaccurate prediction on conformance control efficiency. The correlated model built in this paper can fully describe the polymer concentration change related to inaccessible pore volume and velocity difference based on molecule size to pore size ratio. Results of sensitivity analysis shows that the higher the IPV is, the higher velocity of polymer front and lower concentration of polymer contained in the core. Meanwhile, Frr is sensitive to IPV, and for low permeability zone with ultra-high IPV value, the polymer flooding can barely damage the low permeability zone because Frr in low permeability zone is nearly ignorable.

NOVELTY:

For polymer flooding or gel treatment simulation work in heterogeneous reservoir, a lot of researchers reported that bull head injection operation can lead to severe damage to the oil bearing low permeability zone. In fact, for lab experiments, when fracture or fracture like channel exists in the core sample, the majority of polymer or especially gel treatment will penetrate into high permeability zone instead of low permeability zone. The reason for the erroneous result is strong related to the misleading inaccessible pore volume model for polymer molecules used in current commercial simulation software. Compared with commercial software, this paper’s correlated model can better represent polymer distribution and retention in heterogeneous reservoir. Moreover, the correlation can be easily integrated in commercial software.