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Abstract: Induced seismicity during reservoir stimulation by means of hydraulic fracturing in Enhanced Geothermal System has been a big issue worldwide and has created the need for development of numerical techniques that are capable of simulating hydraulic fracturing and induced seismicity. In this context, this paper presents numerical modeling of hydraulic fracturing in intact/fractured reservoirs and induced seismicity. For this purpose, the commercial software Particle Flow Code 2D is used with additionally implemented fluid flow algorithms and seismicity calculation scheme. Spatial and temporal distributions of induced seismic events are compared with migration pattern of the injected fluid. Results indicate that, in the intact reservoir model, events are induced within the fluid pressurized volume, i.e. defined by a fluid migration front. In contrast to a fractured reservoir model, a large portion of events occur ahead of the fluid front. In the intact model failure occurs due to reduced effective stress associated with fluid pressure increase due to injection. However, the theory of effective stress fails to explain those events occurring ahead of the fluid front in the fractured model, implying that there has to be some other mechanisms, e.g. elastic responses and stress state disturbance of the rock mass to fluid injection that triggers the seismicity in the area where fluid has not infiltrated. In addition we test the effect of the rate of fluid injection and fluid viscosity to understand fracture patterns and distribution of induced seismic events during hydraulic fracturing. 1 INTRODUCTION Seismicity induced by reservoir stimulation by means of hydraulic fracturing in En-hanced Geothermal System is a major issue worldwide. What makes it more difficult to control or mitigate such large magnitude events is that they often occur during depressurization of the wellbore, i.e. after well shut-in.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.46)
ABSTRACT: We present a quasi-static and hydro-mechanical fully coupled approach to the modeling of inter-seismic triggering of seismicity in an arbitrary fractured and fluid-saturated poroelastic solid. The discrete fracture network (DFN) we consider is hybrid and at a dual-scale consisting of large-scale deterministic fractures and small-scale stochastic fractures following certain distributions. The fracture-poro-elasticity fully coupled modeling is carried out using our Jin & Zoback (2017) nonlinear computational model by explicitly resolving the deterministic fractures only. This provides inputs for the subsequent seismicity modeling that accounts for the entire hybrid dual-scale DFN. A new stress updating algorithm is developed accounting for the competing poroelastic stress compensation and seismicity-induced stress loss on fractures. Our model can therefore naturally produce multiple cycles of seismicity triggering. As an example, we perform a numerical experiment and generate a synthetic catalog of induced seismic events, and then analyze (1) seismicity distribution in relation to the fluid pressure, poroelastic stress and fracture distribution, (2) event type, (3) spatial-temporal characteristics, (4) stress history, (5) seismic source parameters and their characteristics and (6) activated DFN and permeability changes. Our modeling provides explanations to some curious observations in real data and can serve as a physics-based tool for predicting induced seismicity in complex geological media.
- Europe (0.93)
- North America > United States > California (0.46)
- North America > United States > Texas (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault (0.93)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.30)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.67)
- North America > United States > Texas > Haynesville Shale Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > United States > Louisiana > Haynesville Shale Formation (0.99)
- (5 more...)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
Discrete Element Modelling of Fluid Injection and Induced Seismicity in a Blocky Structured Rock Mass
Yoon, J. S. (Helmholtz Centre Potsdam GFZ German Research Centre) | Zang, A. (Helmholtz Centre Potsdam GFZ German Research Centre) | Stephansson, O. (Helmholtz Centre Potsdam GFZ German Research Centre) | Hofmann, H. (Helmholtz Centre Potsdam GFZ German Research Centre) | Zimmermann, G. (Helmholtz Centre Potsdam GFZ German Research Centre)
ABSTRACT: In this paper we present a discrete element modelling based fluid injection simulation in a blocky structured rock mass. The hydro-mechanical couple model is developed on the basis of a commercial software, Particle Flow Code 2D. The fluid fl ow algorithm is modified to enable simulation of primary fluid flow through the interfaces between the rock mass blocks and secondary fluid flow into the rock block matrix. The modelling results shows that several key observations in the field of geothermal reservoir stimulation and long-term wastewater disposal are well captured, which include: post shut in seismicity, large magnitude events at the fringe of the seismicity cloud, fluid pressure induced seismicity and poro-elastic stress triggered seismicity at far distance from the injection. In addition, we examined the effect of cyclic injection where there is a relaxation time between the main stimulation cycles. The results show that cyclic injection lowers the seismicity magnitudes, and mitigates the effect of poro-elastic stress triggering. The model is being applied to a few field scale studies, e.g. Enhanced Geothermal Systems and longterm waste water disposal, where a fault zone is present near to the injection and later activated with large seismic events by the fluid injection.
- Europe (0.70)
- North America > United States (0.69)
- Research Report > New Finding (0.68)
- Research Report > Experimental Study (0.54)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.91)
- Water & Waste Management > Water Management (1.00)
- Energy > Renewable > Geothermal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Numerical Investigation of Cyclic Hydraulic Stimulation and Related Induced Seismicity in Pohang Fractured Geothermal Reservoir
Farkas, Marton Pal (University of Potsdam) | Hofmann, Hannes (German Research Centre for Geosciences) | Zimmermann, Gunter (German Research Centre for Geosciences) | Zang, Arno (German Research Centre for Geosciences) | Yoon, Jeoung Seok (German Research Centre for Geosciences)
ABSTRACT: In this study we investigate numerically the flow rate controlled cyclic stimulation experiment performed in August 2017 at the Pohang EGS site using the finite element code FracMan. Per definition, a soft stimulation method aims to increase permeability while reducing the risk of inducing larger seismic events. The numerical code enables studying hydro-mechanical processes and investigating main characteristics of induced seismicity such as spatial evolution of events and their moment magnitude in relation to injected fluid volume in three dimensions. The analysis contributes to understanding the fracturing processes and induced seismicity in naturally compartmentalized fractured reservoir. The code can be also used for predicting the relationship between fluid injection volume and spatial extent of generated or reactivated fractures, i.e. the stimulated reservoir volume. The reservoir model will eventually allow different injection strategies to be investigated to design an optimal stimulation procedure ahead of future field application of soft stimulation. Furthermore, it may also serve as a basis for future numerical investigations.
- North America > United States (1.00)
- Europe (0.70)
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.63)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.95)
Evolution of Induced Seismicity Due to Interactions Between Thermal, Hydraulic, Mechanical And Chemical Processes In EGS Reservoirs
Izadi, Ghazal (Department of Energy and Mineral Engineering, EMS Energy Institute and G3 Center, Pennsylvania State University) | Elsworth, Derek (Department of Energy and Mineral Engineering, EMS Energy Institute and G3 Center, Pennsylvania State University)
ABSTRACT: We explore the complex interaction of coupled thermal, hydraulic, mechanical and chemical (THMC) processes that influence the evolution of EGS reservoirs in general, and in particular with reference to strong, low-permeability reservoirs with or without relic fracturing. We define and describe dominant behaviors that evolve with the evolution of the reservoir: from short-term stimulation through mid-term production and culminating in long-term decline. The injection of fluid under pressure in a rock mass may change the effective stress at early times and result in micro seismicity induced by shear events on reactivated fractures. Changes in thermal stress and chemical changes in the mid- to long-term injection period may also generate seismic activity at later times. In most geothermal reservoirs the induced seismicity results from fluid injection and migrates within the reservoir with time as driven by the various interactions of thermal, hydraulic, mechanical and chemical processes. These processes migrate through the reservoir as fronts at a variety of different length-scales and timescales. We use a continuum model of reservoir evolution subject to coupled THMC processes to explore the evolution of stimulation- and production-induced seismicity in a prototypical EGS reservoir. The model which is discussed here is capable of accommodating changes in stress that result from change in fluid pressure as well as thermal stress and chemical effects. This model is applied to both a single injector and doublet geometry to explore the spatial and temporal migration for triggering of seismicity as stimulation evolves into production. The individual models are realized by different fracture density, fracture distribution (~1m to 100m) and spacing between fractures (~1m to 10m). The approach is successfully calibrated against short-term observations in the Cooper Basin (Australia) and applied to explore the expected evolution of moment magnitude and the triggering of seismicity.
- North America > United States (1.00)
- Oceania > Australia > South Australia (0.27)
- Oceania > Australia > Queensland (0.27)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Oceania > Australia > South Australia > Cooper Basin (0.99)
- Oceania > Australia > Queensland > Cooper Basin (0.99)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)