An Infill Well Fracturing Model and Its Microseismic Events Barrier Effect: A Case in Fuling Shale Gas Reservoir

Abstract

Summary A microseismic (MS) events barrier (MSEB) phenomenon was detected during infill well fracturing of the Fuling shale gas reservoir. This phenomenon was evidenced by MS monitoring results, indicating that when the infill well hydraulic fracture (HF) propagated close to the parent well stimulated region, only a main straight fracture was propagating. Also, the number of seismic events diminished abruptly, suggesting some barrier or an attenuation process for the MS. To clarify the mechanisms involved in the MSEB effect, the infill well fracture propagation is investigated. An integrated workflow is proposed to analyze complex HF propagation of an infill well after the offset parent wells have experienced fracturing and production. The workflow integrates a geological model with natural fractures, a parent well fracturing geomechanical model, a coupled flow-geomechanics production model, and an infill well fracturing geomechanical model. First, a natural fracture network is embedded in the realistic geological model. Second, a geomechanical fracturing model is developed to simulate HF of parent wells. Third, a coupled flow-geomechanics model is used to analyze stress field evolution during parent well production. Fourth, complex HF propagation for the infill well is simulated. The case model is validated with parent well production data and infill well fracturing MS monitoring results. It can be concluded from the simulation results that (1) during parent well production, the pre-existing complex fracture network is a major contributor to pore-pressure decrease; (2) stress evolution is affected by the geomechanical heterogeneity; (3) near the parent well producing fractured region, the fracture complexity of the infill well stimulation decreases sharply and that matches well with the MS monitoring results; and (4) there are two primary mechanisms that are responsible for the MSEB phenomenon—natural fracture (NF) activation during parent well fracturing and stress evolution in parent well production. The Fuling shale gas reservoir infill well fracturing case study reveals the mechanism of the MSEB effect by demonstrating the impact of parent well production on infill well fracturing. To serve the fracture-hits evaluation and to maximize the stimulated reservoir volume (SRV), the MSEB effect should be taken into consideration in infill well fracturing design.