Cluster Spacing Optimization for Horizontal-Well Fracturing in Shale Gas Reservoirs: Modeling and Field Application

Multi-stage fracturing in horizontal well is the core technology for commercial exploitation of shale gas reservoir, in which the cluster spacing plays an important role to impact the fracturing performance—undersized cluster spacing might make the stimulated reservoir volume (SRV), activated by different hydraulic fractures, excessively overlap with each other, while oversized cluster spacing might leave unstimulated regions between neighboring hydraulic fractures; in either case the fracturing would be inefficient. However, most current cluster spacing design methods are imperfect without a reliable SRV estimation model. This paper established a numerical model to estimate the SRV by simulating four key processes during multi-stage fracturing—hydraulic fractures propagation, formation stress changing, reservoir pressure lifting, and natural fractures failure. Then, based on this SRV model, an optimization method for cluster spacing was proposed and applied in Fuling shale gas field in Southwest China. We analyzed the influence of geological conditions and fracturing parameters on the optimal cluster spacing, and drew the reference charts for cluster spacing design in Fuling gas field. This research developed an effective cluster spacing optimization method, reduced the uncertainty in cluster spacing design, and provided some new insights on the optimal design of multi-stage fracturing in horizontal shale gas well.