Impact of Geologic Heterogeneity on Multiphase Flow as Simulated with Different Discretisation Schemes and Constitutive Relationships

Stephan Matthai and Qi Shao and Luat Tran and Abdallah Youssef and Kuncho Kurtev. ( 2019 )
in: 2019 Ring Meeting, ASGA

Abstract

Sedimentary sequences are heterogeneous so that fingering is expected during the unstable displacement that ensues from gas injection (mobility ratio M> 1, large viscosity contrast, unfavourable gravitational to viscous force balance). Even in highly permeable, relatively uniform strata single-phase mobility variations marking bedforms and differences in depositional patterns, should become amplified during multiphase flow as the low-viscosity gas selectivelydisplaces high-viscosity oil or water from high-permeability streaks, imparting a memory of pastinjection events on such heterogeneous systems. Extensive experience with hydrocarbon gas reinjection in the North Sea corroborates these theoretical predictions and provides evidence that even for first- or multiple contact miscible displacement, small-scale fluid-phase segregation can cause flow-structure effects that can lead to segregated ow on the large-scale, causing early breakthrough of gas to producer wells in some cases. Water-Alternating-Gas (WAG) schemes have been invented to suppress such coarsening instabilities. Are any of such instabilities and scale-transgressive flow patterns observed in numeric simulations? - and, given the nested nature of geologic heterogeneity, is the spreading of gas plumes ergodic? - This study investigates these questions with numeric simulations conducted using 3 different discretisation approaches applied to models of highly permeable fluvial-to-deltaic sedimentary sequences: 1) the industry-standard finite-difference method applied to structured corner-point grids, 2) finite-elements treated as control volumes, 3) the hybrid finite element - finite volume method. While approach (1) requires some regularisation of the flow geometry, (2) and (3) are applied to adaptively refined meshes conforming with the sedimentary features. Preliminary results show dramatic differences in plume shape and gas sweep predicted by the different methods, supporting that - in the face of uncertainty - one should always try different approaches to get a realistic estimate of the uncertainty that is associated with production and performance forecasts for heterogeneous systems. Detailed outcomes of the study will be reported in this presentation.

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BibTeX Reference

@INPROCEEDINGS{MatthaiRM2019,
    author = { Matthai, Stephan and Shao, Qi and Tran, Luat and Youssef, Abdallah and Kurtev, Kuncho },
     title = { Impact of Geologic Heterogeneity on Multiphase Flow as Simulated with Different Discretisation Schemes and Constitutive Relationships },
 booktitle = { 2019 Ring Meeting },
      year = { 2019 },
 publisher = { ASGA },
  abstract = { Sedimentary sequences are heterogeneous so that fingering is expected during the unstable displacement that ensues from gas injection (mobility ratio M> 1, large viscosity contrast, unfavourable gravitational to viscous force balance). Even in highly permeable, relatively uniform strata single-phase mobility variations marking bedforms and differences in depositional patterns, should become amplified during multiphase flow as the low-viscosity gas selectivelydisplaces high-viscosity oil or water from high-permeability streaks, imparting a memory of pastinjection events on such heterogeneous systems. Extensive experience with hydrocarbon gas reinjection in the North Sea corroborates these theoretical predictions and provides evidence that even for first- or multiple contact miscible displacement, small-scale fluid-phase segregation can cause flow-structure effects that can lead to segregated ow on the large-scale, causing early breakthrough of gas to producer wells in some cases. Water-Alternating-Gas (WAG) schemes have been invented to suppress such coarsening instabilities. Are any of such instabilities and scale-transgressive flow patterns observed in numeric simulations? - and, given the nested nature of geologic heterogeneity, is the spreading of gas plumes ergodic? - This study investigates these questions with numeric simulations conducted using 3 different discretisation approaches applied to models of highly permeable fluvial-to-deltaic sedimentary sequences: 1) the industry-standard finite-difference method applied to structured corner-point grids, 2) finite-elements treated as control volumes, 3) the hybrid finite element - finite volume method. While approach (1) requires some regularisation of the flow geometry, (2) and (3) are applied to adaptively refined meshes conforming with the sedimentary features. Preliminary results show dramatic differences in plume shape and gas sweep predicted by the different methods, supporting that - in the face of uncertainty - one should always try different approaches to get a realistic estimate of the uncertainty that is associated with production and performance forecasts for heterogeneous systems. Detailed outcomes of the study will be reported in this presentation. }
}