Comprehensive Characterization of the Unconventional Fracture Networks via Fiber Optic Tools and Microseismicity Analysis

Abstract The 4D unconventional fracture network evolution, especially considering the closure state of hydraulic fractures during fracturing stimulations and shale gas productions is not well understood. This paper proposed a novel method to characterize 4D unconventional fracture network evaluations considering dynamic closure of unconventional fractures based on a 4D Hydro-geomechanical model and fiber optics monitoring. First, we summarized the geological deposition, tectonic features and organic matter resources of the Marcellus shale gas reservoir, and the gas decline law was used to fit and predict the production characteristics of horizontal wells in a certain drilling platform. The unconventional fracture extension simulation was carried out, which combined with microseismic monitoring data to reveal the fracture geometry and stimulation scale: the average propped fracture length of the 22 stages fractured in the well MIP-3H was 120.18 m (394.30 ft), with a height of 23.37 m (77.67 ft). The width of hydraulic fractures was about 1.52 mm (0.06 in) near the wellbore, and the average conductivity was 116.57 mD·m (382.45 mD·ft). Based on the fracture parameters, the four-dimensional (3D + time) reservoir flow and geomechanics coupled model were solved with the finite element method through numerical simulation. During gas production, the formation pressure gradually decreases while the effective stress increases and the reservoir appears a slight deformation. At the fracture surface, the deformation is relatively obvious due to the high effective stress, showing the closure phenomenon finally. In addition, the fracturing and coupled model analysis was validated using the distributed fiber-optic temperature sensing (DTS) monitoring data obtained in the field, which confirms that the dynamic fracture closure does occur in the fractured stage 9 of the MIP-3H well. This work can guide the fracturing design and production prediction of subsequent shale gas development and is of great importance for effective shale resource development.