Characterization of the Amount of Swept and Unswept Fractions Between Two Wells in the Presence of Reservoir Anisotropy

Abstract

The reservoir heterogeneity controls interwell connectivity and affects reservoir dynamics. An approach is to use continuum percolation to study the flow behavior of low to intermediate net-to-gross reservoirs. In this study, reservoir models with a permeability contrast have been used, and the interwell connectivity between two wells and the remaining unswept oil has been determined. The percolation parameters, including the amount of recoverable oil connected between two wells and the amount of unswept oil (also referred to as dangling end fraction (that control fluid displacement (e.g. waterflooding) vary as a function of sand body size and reservoir size. These properties show a power-law function of net-to-gross (i.e. occupation fraction) with some exponents called critical exponents. There exist a few publications on the numerical values of these parameters. The main contribution of this study is to investigate the effects of reservoir anisotropy on the percolation parameters. To determine the swept (backbone) fraction connected between two wells, the flow-based criteria depending on the system size have been proposed. The results show that the critical exponents for the backbone and dangling ends are in the range of 0.3to 0.45 and -0.45 to -0.20. It is notified that the limitation to perform simulations on infinite systems results in a range for these exponents, although there exist unique values for infinite systems. Moreover, a sensitivity analysis is implemented to find the correct flow-based criteria for the backbone. The results of this study extend the applicability of the percolation properties curves for anisotropic reservoirs.

Keywords

• continuum percolation
• heterogeneity
• reservoir connectivity
• backbone
• dangling ends
• anisotropy