Fracture sealing and its impact on the percolation of subsurface fracture networks

Abstract

Current uderstanding of the impact of fracture sealing on macro-scale fluid flow is insufficient. Here, we generate well-connected orthogonal fracture networks in two- and three-dimensions using a discrete fracture network method. The fracture sealing is simulated by dividing fractures into segments (2D) and blocks (3D). Impacts of fracture sealing on the percolation status of orthogonal fracture networks are systematically studied. Different aperture shapes, segment lengths, and spacing distributions are broadly considered. We find that a small amount of sealing can prevent the formation of spanning clusters, suggesting that global connectivity is rarely realized. Local clusters can trigger hydraulic responses if their sizes are large enough. The connectivity reduction caused by fracture sealing can be reversed by significant stress perturbations, such as hydraulic fracturing. The well-connected and critically oriented fractures become critically stressed and slide because of the increased pore pressure. Partially sealed and mechanically stable fractures can also contribute to fluid flow by enlarging the stimulated reservoir volume (SRV). A new procedure to estimate the SRV size is proposed, and the estimated results are qualitatively consistent with microseismicity maps and field observations.