Characterization of the amount of swept fraction (i.e. backbone) and unswept fraction (i.e. dangling ends) between two wells in presence of reservoir anisotropy

Document Type : Research Paper


Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran



The reservoir heterogeneity controls interwell connectivity and affect reservoir dynamics. An approach is to use continuum percolation that is adopted to study the flow behavior of low to intermediate net-to-gross reservoirs. In this work, we use reservoir models with a permeability contrast and determine the interwell connectivity between two wells and the remaining unswept oil. The percolation parameters including the mount of recoverable oil connected between two wells and the amount of unswept oil (also referred to as the backbone and dangling end fractions, respectively) that controls fluid displacement (e.g. waterflooding) varies as a function of sandbody 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 work is to investigate the effects of reservoir anisotropy on the percolation parameters. To determine the backbone fraction connected between two wells we propose flow-based criteria depending on the system size. The results show that the critical exponents for the backbone and dangling ends are in the range of [0.3, 0.45] and [-0.45, -0.20]. It is notified that the limitation to perform simulations on infinite systems results in a range for these exponents, although there exists 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 work extend the applicability of the percolation properties curves for anisotropic reservoirs.