Numerical Modeling of Unstable Water Floods and Tertiary Polymer Floods into Highly Viscous Oils

Abstract

The saturation distribution after unstable water flooding into highly viscous oil may have a decisive impact on the efficiency of tertiary polymer flooding, in particular due to hysteresis effects associated with oil banking. In this work, we model water flood and tertiary polymer flood experiments performed on Bentheimer sandstone slabs with heavy oils of about 2000 cP and 7000 cP, and compare the numerical results with experimental production, pressure and X-ray data. The unstable water floods are initially simulated in 2D with our parallel in-house research reservoir simulator using a high-resolution discretization. In agreement with existing literature, we find that Darcy-type simulations based on steady-state relative permeabilities - inferred here from a 3D quasistatic pore network model (PNM) - cannot predict the measured water flood data. Even qualitatively, the viscous fingering patterns are not reproduced. An adaptive dynamic pore network model is then applied on a 2D pore network constructed from the statistics of the 3D network. If the fingering patterns simulated with this 2D PNM are qualitatively in good agreement with the experimental data, a quantitative match cannot be obtained due to the limitations of 2D modeling. Although 3D dynamic PNM at the slab scale would currently lead to prohibitively high computational cost, it has the potential to address the deficiencies of continuum models at highly unfavorable viscosity ratio. For the tertiary polymer floods characterized by a much more favorable mobility ratio, Darcy-type modeling is applied and history matching is conducted from the end of the water floods. We find that unless hysteresis due to oil banking is accounted for in the relative permeability model, it is not possible to reconcile the experimental data sets. This hysteresis phenomenon, associated with oil invasion into previously established water channels, explains the rapid propagation of the oil bank. For the considered experiments, a simultaneous history match of good quality is obtained with the production and pressure data, and the simulated 2D saturation maps are in reasonable agreement with X-ray data. This paper addresses the challenges in modeling highly unstable water flooding, using both a conventional Darcy-type simulator and adaptive dynamic PNM, by confronting the simulated results with experimental data including saturation maps. It also highlights the important role of relative permeability hysteresis in the tertiary recovery of viscous oils by polymer injection.

Viscous Fingering and Preferential Flow Paths in Heterogeneous Porous Media

“…At breakthrough, the subnetwork { NW } B becomes connected (in the sense discussed in sections 2.1 and 2.2) and can be compared to { R c } and { Q c }. To validate our computer code, we simulated the waterflooding experiment reported in de Loubens et al (2018) and compared our result to de Loubens et al's X‐ray image of the waterflooded pore space at breakthrough as well as their 2‐D dynamic network simulation. We found that the simulated injection pattern was in good qualitative agreement with de Loubens et al's experimental and simulation results (see supporting information section S5).…”

Polymer Flooding at an Adverse Mobility Ratio: Acceleration of Oil Production by Crossflow into Water Channels

“…The capillary pressure curves included in the sensitivity analysis are given in Figure 19. The primary drainage curve is obtained from de Loubens et al 36 The forced imbibition curves for water and polymer are obtained from unpublished laboratory work conducted at Uni Research CIPR, Norway.…”

Investigation of waterflood front digitations during immiscible displacements in porous media

“…Fingering has been observed to occur at all scales ranging from the phases by-pass at pore level [16] to the phases partitioning at reservoir level, causing severe early waterbreakthrough. The magnitude of their dimensions variation causes its modelling to be a perilous task using Darcy's scale models [17]. A possible alternative is to upscale flow dynamics properties from laboratory experiments, to account for the complexity of these flows at higher scale resolution [18].…”

“…Still they are by nature limited in dimensions and connectivity [20,22]. Slab experiments conducted on Bentheimer samples have allowed to look further in the 2D fingerings characterization [17,23]. However, the core width is restricted with these experiments, leading to high dimensions ratio that strongly affect the fingers growth as demonstrated by Doorwar and Mohanty in [24].…”