水圧刺激・水圧破砕技術の最新動向（2）

[3309-15-01] Numerical simulation of an in-situ fluid injection experiment with a coupled X-FEM analysis

○Adam Schwartzkopff¹, Atsushi Sainoki¹ (1. Kumamoto University)

司会:陳 友晴(京都大学)

Keywords:Extended finite element method, Coupled analysis, Fluid injection

Fluid injection into the earth’s crust is frequently associated with induced slip, which is known to cause seismicity. However, it is difficult to predict seismic events from fluid injection, associated with activities such as hydraulic fracturing for destressing in deep hard rock mines, geothermal energy and unconventional hydrocarbon production. Hence, a two-dimensional static extended finite element method (X-FEM) code has been written in Matlab with coupled fluid and mechanical analysis capabilities, which allows for not only fluid flow within a discontinuity but also the fluid exchange between the discontinuity and the surrounding permeable medium, to assist the prediction of the mechanical behavior of a fault from fluid injection. A comparative model is generated using this code and the results are compared to a previously published in-situ experiment, where they injected fluid into a fault at a great depth and directly measured pressure increase, induced slip, opening displacement and seismic events. The input to the model is the injection flow rate of the in-situ experiment. This flow rate generates the pressure increase at the injection point. The injection of water in the model increases the pressure elsewhere in the model by permeating through the fault and the rock mass. The pressure increase at the injection point of the model agrees well compared with the in-situ experimentally measured result. In addition, from the simulation the normal and shear displacements at the injection point follow a similar trend to the in-situ experiment. This suggests that the behavior of this fault can be modelled using this approach. This model could be used to assist the prediction of the mechanical behavior of other faults from fluid injection, which could eventually lead to the prediction of induced seismicity caused by the previously mentioned engineering activities, resulting from hydraulic fracturing operations.