Determination of the optimal spacing of water curtain boreholes for underground oil storage from the perspective of percolation theory

Abstract

The spacing of water curtain boreholes is important for underground oil storage. It was usually determined using empirical method, in this study, a method for determining the optimal spacing of water curtain boreholes for underground oil storage was developed from the percolation theory of fractured rock masses. The connectivity of fractured rock masses with different fracture densities and geometric parameters was investigated considering two typical flow configurations, i.e., unidirectional and radial flow configurations. The percolation threshold was defined as the critical value with increasing fracture trace length. It was found that the percolation threshold in the unidirectional flow configuration was higher than that in the radial flow configuration. From the perspective of percolation theory, a method was developed for evaluating fracture network connectivity. In this method, the probability of connection of water curtain boreholes was related to a percolation parameter, which depended on the fracture density and trace length. The spacing of water curtain boreholes for the Huangdao underground oil storage facility was determined using the proposed method. The optimal spacing of the water curtain boreholes was validated against the connectivity tests in the field, indicating that the determined spacing was reasonable and that this method can provide guidance for the design of water curtain boreholes for other underground oil storage facilities.