Characterization of seismic energy during fault-slip induced by fluid injection using coupled and dynamic X-FEM analysis. Issue 3 (October 2021)

• Record Type: Journal Article
• Authors: Schwartzkopff, Adam K; Sainoki, Atsushi
• Is Part Of: IOP conference series. Volume 861:Issue 3(2021)
• Publication Date: 2021-10
• Subjects: Earth sciences -- Periodicals; Environmental sciences -- Congresses; Environmental sciences -- Periodicals; 550.5
• DOI: 10.1088/1755-1315/861/3/032078
• Languages: English
• ISSNs: 1755-1307

Abstract

Abstract: Fluid injection into a rock mass from industrial processes can lead to reactivation of pre-existing faults at great depths. When the shear behaviour involves dynamic rupture, perceivable seismic events could be induced that may raise public concern. This seismicity can be caused by injection-induced fluid pressure in the rock mass causing slip on faults. This study provides a method to distinguish between aseismic and seismic fault movement induced by anthropogenic fluid injection with the aim of gaining an insight into the difference in seismic source parameters between the two types of fault behaviour, i.e., seismic and aseismic. This was achieved by using a two-dimensional fully coupled fluid and mechanical loading extended finite element model (X-FEM) with a dynamic analysis module. This code considers fluid flow along the fault as well as into the rock mass and uses a directly proportional equivalent injected flow rate into the fault as the input. This model was validated by comparing the resultant pressure and normal and shear displacements calculated at the centre of the fault against observations from a decametre-scale in-situ experiment. The main results were that not only the mechanics of the fault could be simulated using this approach, but the simulation correctly predicted the onset of seismicity and transition to dynamic analysis and at similar seismic magnitudes to observations. In terms of the difference in seismic source parameters between seismic and aseismic fault movements, it was shown that while the seismic shear movement to total shear movement is approximately 1%, the dynamic analysis produces approximately 75% of the total near field energy released in the simulation. This indicates the necessity of distinguishing dynamic and quasi-static shear movements in the numerical simulation of fluid injection-induced seismicity in order to quantify magnitude and seismic energy released accurately and to assess the risk of seismicity properly, since aseismic fault movements do not cause any damage to facilities on the surface. These results are important, since they demonstrate the applicability of this X-FEM approach in accurately predicting the mechanics of fault reactivation and the resultant seismicity, aiding in the design and scheduling of fluid injection and in the optimization of operational parameters.