Role of Fluid Diffusivity in the Spatiotemporal Migration of Induced Earthquakes during Hydraulic Fracturing in Unconventional Reservoirs

Abstract

Hydraulic-fracturing-induced earthquakes exhibit an intricate pattern in spatiotemporal migration with respect to stage completions of fracturing horizontal wells. The underlying physical mechanisms remain uncertain. This paper investigates two field cases to quantify the effects of fluid diffusivity on the spatiotemporal migration of induced earthquakes during fracturing stimulation in shale reservoirs. First, the double-couple component approach is employed to determine the focal mechanisms of mainshock events. The relation plot of earthquake magnitude− fault size as well as the spatial distribution of induced events are used together to characterize the fault distribution. Then, the tight rock analysis and triaxial compression experiments are conducted to determine the distinctive petrophysical and geomechanical properties of stimulated formations in both cases. The hydraulic diffusivity of fracturing fluids is then estimated from the spatiotemporal evolution of the seismicity fronts with respect to the fracturing sites. Finally, a poroelastic modeling and numerical simulation are performed to evaluate the time-dependent pore pressure diffusion and poroelastic stress perturbation during fracturing stimulations. Results suggest that the subvertical N−S-trending faults and NE45°-trending hydraulic fractures generate the fracture and fault networks in the M w 3.6 and M w 3.4 cases, providing geological evidence to account for the spatial distribution of induced earthquakes within the networks. The shear stress gradient G is calculated to be 0.21 MPa/km for the M w 3.6 case and −0.08 MPa/km for the M w 3.4 case, indicating downward and slightly upward shear growth. The observed seismicity migration defines the hydraulic diffusivity of 0.15 m 2 /s for the M w 3.6 event and 2 m 2 /s for the M w 3.4 event. The poroelastic simulation characterizes the time-dependent pore pressure and poroelastic stress changes, matching well with the spatiotemporal migration of induced earthquakes during and after fracturing stimulations. The increasing pore pressure is the first-order factor in fault reactivation. Different time lags between stage completions and induced earthquakes indicate distinctive fluid diffusivity within the hydraulic fracture and seismogenic fault networks.

Research on the impact of pre‐existing geological fractures on hydraulic fracturing in high in situ stress environments

“…Field testing is the most accurate way to get an accurate understanding, but field testing is too expensive to conduct large‐scale studies, 6 It may be used when studying issues related to geological hazards, such as the effects of hydraulic fracturing on faults 7 . Hui et al 8 studied the effects of hydraulic fracturing on seismic activity by collecting data from onsite hydraulic fracturing to develop fracture propagation models for unconventional hydraulic fracturing. Among all the methods, the most widely used method is the numerical simulation method, because it is simple, fast, low cost, and has low requirements for equipment and working environment, and considers many influencing factors, and can complete some operations that are difficult to achieve in conventional tests 9 .…”

Study on the Flow Behavior of Gas and Water in Fractured Tight Gas Reservoirs Considering Matrix Imbibition Using the Digital Core Method

“…Their notable low permeability and intricate pore formations characterize these reservoirs; tight gas reservoirs exhibit poor gas mobility, resulting in the low efficiency of traditional oil and gas extraction techniques in tight reservoir development [4][5][6][7]. Hydraulic fracturing technology, which fractures reservoir rocks with high-pressure fluids to increase rock permeability, enabling gas to flow and be effectively extracted, is a key technology for developing tight gas reservoirs [8][9][10][11]. Inherent water saturation exists within tight sandstone deposits, and the process of fracturing introduces substantial water volumes into these deposits.…”

Knowledge Extraction via Machine Learning Guides a Topology‐Based Permeability Prediction Model

“…Understanding the behavior of fluid flow is crucial in numerous technological and engineering fields such as groundwater movement (Wang et al., 2023), oil and gas recovery (Hui et al., 2023), geological CO 2 sequestration (Fareed et al., 2023), hydraulic fracking (B. Chen et al., 2022) and internal erosion (Han & Kwon, 2023). It is important to accurately delineate the flow physics of these fluids to maintain water resource security, increase energy availability and guarantee engineering safety.…”