Theoretical analysis of ground displacements induced by deep fluid injection based on fully-coupled poroelastic simulation

Abstract

Observations of surface displacements are expected to aid in geomechanical analyses of injection-induced seismicity. However, the controlling factors of the displacement magnitude remain poorly understood except the elastic modulus of the fluid-bearing reservoir. Here, an experiment scheme of numerical simulation based on fully-coupled poroelasticity is designed to investigate the displacements induced by deep underground fluid injection. According to the sealing ability of deep reservoirs, the numerical experiments are classified into two scenarios: injection into open and sealed reservoirs. Potential effects from both geological and operational parameters are considered during the experiments, which include the hydromechanical properties, the reservoir geometry, injection rates and volumes. Experimental results reveal that in addition to the reservoir depth and Young's modulus, the porosity also has significant influences on the surface displacements. Geodetic modeling of injection-induced displacements should include the parameter of reservoir porosity. When the reservoir is characterized by a good sealing ability, fluid injection is prone to induce larger horizontal displacements than vertical uplifts. Most of injection activities including hydraulic fracturing can probably induce detectable surface displacements. Geodetic surveying, especially using Global Navigation Satellite System (GNSS) with both horizontal and vertical observations, should become an essential monitoring task for anthropogenic fluid injection/production activities, which is conducive to assess and mitigate some geohazards including earthquakes.