Reservoir Microearthquake Modeling Analysis: a Proof-of-concept Study and Its Application to Injection Fluid-Induced Seismicity

Abstract

Microearthquakes (MEQs) occur when fluid is reinjected into the reservoir, raising the pressure in the vicinity of the injection well. The pressure build-up in the reservoir due to fluid injection decreases the rock yield strength, which causes shear failure, thus triggering a seismic event. This mechanism presents a further opportunity to use microseismicity as a means to calibrate reservoir parameters, particularly the active faults which tend to be the most conductive fluid flow pathways. The study aims to integrate MEQ modelling to the reservoir development workflow and to the calibration workflow to estimate the permeability of the formations and the faults. The proof-of-concept study considers a synthetic induced seismicity model which represents an area where the fluid is being injected. Reservoir simulation is conducted to evaluate pressure migration through the reservoir for a given reservoir and fault parameters. The earthquake model uses the pressure change from the simulation to compute the average seismicity rate of the fault as well as the spatiotemporal evolution of the seismic events. Synthetic MEQ data is then generated from the earthquake simulation using the Poisson model, which serves as the data for calibration and inverse modelling. Synthetic inversion is then performed to estimate the permeability of both the reservoir and the fault using Markov Chain Monte Carlo (MCMC) sampling method. The study also includes the effects of variation in MEQ data and other uncertainties in the model in parameter estimation. The method developed in this study is then applied to an injection fluid-induced seismicity from a wastewater injection site.