Estimation of sub-core permeability statistical properties from coreflooding data

• Published in: Advances in water resources 2017-10, Vol.108, p.113-124
• Main Author: Rabinovich, Avinoam
• Format: Article
• Language: English
• Subjects: Accuracy; Anisotropy; Brine; Brines; Capillary limit; Capillary pressure; Carbon dioxide; CO2-brine coreflooding; Core flow; Coreflooding experiments; Correlation; Data; Effective properties; Horizontal orientation; Membrane permeability; Methods; Modelling; Normal distribution; Permeability; Power law; Ratios; Relative permeability; Saline water; Statistical analysis; Studies; Sub-core permeability; Variance
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/j.advwatres.2017.07.012

•Method for estimating sub-core log-permeability mean and variance is proposed.•Semi-analytical formula derived for capillary limit effective relative permeability.•Method is based on matching formula to coreflooding experimental measurements.•Method is validated on synthetic data and CO2-brine coreflooding experiment results. Knowledge of sub-core permeability is necessary for accurate numerical modeling of coreflooding experiments and for investigation of sub-core flow phenomenon. A new method for estimating sub-core permeability geometric mean (kG) and log-permeability variance (σy2) is presented. The method is based on matching coreflooding experiment measurements of wetting phase relative permeability with semi-analytical calculations of effective relative permeability. The semi-analytical solution is formulated assuming log-normal permeability (k), steady state and capillary-limit conditions. It is based on the geometric mean and log-phase-permeability variance for isotropic k and power law averaging for anisotropic correlations. The solution is validated on synthetic k realizations by comparison with numerical calculations. Then, the estimation method is tested on synthetic data assuming various types of core capillary pressure relationships, relative permeability functions and k anisotropies. Results demonstrate high accuracy in almost all of the cases except for small anisotropy ratios lh/lv between horizontal (lh) and vertical (lv) dimensionless correlation lengths, where flow is in the horizontal direction, and when σy2 is large. The method is also validated using data from CO2-brine coreflooding experiments conducted on two different cores. It is found that the estimation method remains accurate in these realistic settings, however, accuracy of kG is reduced when the core permeability departs from a log-normal distribution.