Tracer- and Pressure-Test Analysis for Characterization of Areally Heterogeneous Reservoirs

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Abstract
Summary: This study compares simulated well-to-well tracer and transient pressure tests in a quadrant of a repeated five-spot with spatial variations in permeability. Single-layer heterogeneous media with an autocorrelated and log-normal permeability distribution are generated with a stochastic moving-average method. Finite-difference simulation of pressure behavior in these systems indicates that the geometric mean of effective permeabilities around injection and production wells is a good approximation for the steady-state interwell permeability. A dimensionless permeability difference, defined in terms of these quantities, correlates with a heterogeneity index, defined as the product of permeability variance and a dimensionless correlation length scale. Tracer flow is simulated with a particle-tracking procedure. Simulations show that when the heterogeneity index is small, tracer response can be matched with solutions of the convection-dispersion equation with a constant dispersivity that is proportional to the heterogeneity index. For larger values of this index, preferential flow paths are created that cause tracer-breakthrough curves to behave as though they result from flow in a layered system. A method is proposed to estimate the heterogeneity index from pressure-test data and thus to predict the nature of the tracer response qualitatively.

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