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Title: Integrated Geomechanics and Geophysics in Induced Seismicity: Trigger Physics.

Abstract

Abstract not provided.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1405249
Report Number(s):
SAND2016-10626PE
648484
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the KOGAS held October 28-21, 2016 in Albuquerque, NM.
Country of Publication:
United States
Language:
English

Citation Formats

Yoon, Hongkyu, Dewers, Thomas, Knox, Hunter Anne, Bower, John Eric, Pyrak-Nolte, Laura, and Bobet, Antonio. Integrated Geomechanics and Geophysics in Induced Seismicity: Trigger Physics.. United States: N. p., 2016. Web.
Yoon, Hongkyu, Dewers, Thomas, Knox, Hunter Anne, Bower, John Eric, Pyrak-Nolte, Laura, & Bobet, Antonio. Integrated Geomechanics and Geophysics in Induced Seismicity: Trigger Physics.. United States.
Yoon, Hongkyu, Dewers, Thomas, Knox, Hunter Anne, Bower, John Eric, Pyrak-Nolte, Laura, and Bobet, Antonio. 2016. "Integrated Geomechanics and Geophysics in Induced Seismicity: Trigger Physics.". United States. doi:. https://www.osti.gov/servlets/purl/1405249.
@article{osti_1405249,
title = {Integrated Geomechanics and Geophysics in Induced Seismicity: Trigger Physics.},
author = {Yoon, Hongkyu and Dewers, Thomas and Knox, Hunter Anne and Bower, John Eric and Pyrak-Nolte, Laura and Bobet, Antonio},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month =
}

Conference:
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  • The production of geothermal energy from dry and low permeability reservoirs is achieved by water circulation in natural and/or man-made fractures, and is referred to as enhanced or engineered geothermal systems (EGS). Often, the permeable zones have to be created by stimulation, a process which involves fracture initiation and/or activation of discontinuities such as faults and joints due to pore pressure and the in-situ stress perturbations. The stimulation of a rock mass is often accompanied by multiple microseismic events. Micro-seismic events associated with rock failure in shear, and shear slip on new or pre-existing fracture planes and possibly their propagations.more » The microseismic signals contain information about the sources of energy that can be used for understanding the hydraulic fracturing process and the created reservoir properties. Detection and interpretation of microseismic events is useful for estimating the stimulated zone, created reservoir permeability and fracture growth, and geometry of the geological structures and the in-situ stress state. The process commonly is referred to as seismicity-based reservoir characterization (SBRC). Although, progress has been made by scientific & geothermal communities for quantitative and qualitative analysis of reservoir stimulation using SBRC several key questions remain unresolved in the analysis of micro-seismicity namely, variation of seismic activity with injection rate, delayed micro-seismicity, and the relation of stimulated zone to the injected volume and its rate, and the resulting reservoir permeability. In addition, the current approach to SBRC does not consider the full range of relevant poroelastic and thermoelastic phenomena and neglects the uncertainty in rock properties and in-situ stress in the data inversion process. The objective of this research and technology developments was to develop a 3D SBRC model that addresses these shortcomings by taking into account hydro-thermo-poro-mechanical mechanisms associated with injection and utilizing a state-of-the-art stochastic inversion procedure. The approach proposed herein is innovative and significantly improves the existing SBCR technology (e.g., Shapiro et al. 2003) for geothermal reservoirs in several ways. First, the current scope of the SBRC is limited with respect to the physical processes considered and the rock properties used. Usually, the geomechanics analyses within SBRC is limited to the pore pressure diffusion in the rock mass, which is modeled using a time-dependent parabolic equation and solved using a finite element algorithm with either a line or a point source. However, water injection induces both poroelastic and thermoelastic stresses in the rock mass which affect the stress state. In fact, it has been suggested that thermoelastic stresses can play a dominant role in reservoir seismicity (Ghassemi et al., 2007). We include these important effects by using a fully-coupled poro-thermoelastic constitutive equations for the rock mass which will be solved using a 3D finite element model with more realistic injection geometries such as multiple injection/extraction sources (and in fractures), uncertainty in the material parameters and the in-situ stress distribution to better reflect the pore pressure and stress distributions. In addition, we developed a 3D stochastic fracture network model to study MEQ generation in fracture rocks. The model was verified using laboratory experiments, and calibrated and applied to Newberry EGS stimulation. In previous SBRC approaches, the triggering of micro-seismicity is modeled base on the assumption that the prior stochastic criticality model of the rock mass is a valid and adequate description. However, this assumption often does not hold in the field. Thus, we improved upon the current SBRC approach by using the micro-seismic responses to estimate the hydraulic diffusivity as well as the criticality distribution itself within the field. In this way, instead of relying on our a priori knowledge of criticality distribution, we combine an initial probabilistic description of criticality with the information contained in microseismic measurements to arrive at criticality solutions that are conditioned on both field data and our prior knowledge. Previous SBRC have relied upon a deterministic inversion approach to estimate the permeability, and the extent of the stimulated zone, whereas a stochastic inversion algorithm that recognizes and quantifies the uncertainties in the prior model, the time evolution of pore pressure distributions (modeling errors), and the observed seismic events is developed and used herein to realistically assess the quality of the solution. Finally, we developed a technique for processing discrete MEQ data to estimate fracture network properties such as dip and dip directions. The approach was successfully applied to the Fenton Hill HRD experiment and the Newberry EGS with results in good agreement with field observations.« less
  • Understanding the processes that enhance fluid flow in crustal rocks is a key step towards extracting sustainable thermal energy from the Earth. To achieve this, geoscientists need to identify the fundamental parameters that govern how rocks respond to stimulation techniques, as well as the factors that control the evolution of permeability networks. These parameters must be assessed over variety of spatial scales: from microscopic rock properties (such as petrologic, mechanical, and diagenetic characteristics) to macroscopic crustal behavior (such as tectonic and hydro-dynamic properties). Furthermore, these factors must be suitably monitored and/or characterized over a range of temporal scales before themore » evolutionary behavior of geothermal fields can be properly assessed. I am reviewing the procedures currently employed for reservoir stimulation of geothermal fields. The techniques are analyzed in the context of the petrophysical characteristics of reservoir lithologies, studies of wellbore data, and research on regional crustal properties. I determine common features of geothermal fields that can be correlated to spatiotemporal evolution of reservoirs, with particular attention to geomechanics and petrophysical properties. The study of these correlations can then help guide procedures employed when targeting new prospective geothermal resources.« less
  • The Lawrence Livermore (LLNL) and Los Alamos (LANL) National Laboratories of the U.S. Department of Energy perform high-energy physics experiments in an underground mine, the Ula complex, at the Nevada Test Site. The mine-operating contractor is Bechtel Nevada Corporation (BN). The peculiarity of this mine is that it is in an alluvium with an unconfined compressive strength of about 1 MPa, at a depth of 300m. So, the in-situ vertical stress is about 6 MPa. Two shafts mark the north and south boundaries of the Ula complex, the Ulh (brand new) and Ula (older) shafts respectively. Their centerlines are separatedmore » by a distance of 510 m. The east-west dimension of the complex currently is about 340 m. The drifts and chambers are horizontal and have a width up to 6.6 meters and a height up to 5.1 meters, with locally larger openings at the shaft stations. The drifts are excavated using an Alpine Miner and are taken in two steps, heading and bench, or full heading. At present, ground support is by means of 2.4 m to 5.1 m long rock bolts and wire mesh, that are covered by a 7.5 to 15-cm layer of steel-fiber reinforced shotcrete applied as a dry mix. A few years ago, some significant distress was observed in the shotcrete and the bare alluvium at several locations in the complex. In addition, significant yielding of the ground was surmised at load transfer distances of up to 60 meters. At that time, there were only a minimal number of diagnostic instruments to provide any understanding of the ground behavior. A Mining Review Board was formed in 2000, and a geomechanics program was designed and implemented to guide future expansion of the complex. The paper describes the geomechanics results and their interpretation. Several areas are discussed: (1) Strength properties of rock material; potential scale effects. (2) Rock mass deformation: multi-position extensometer and closure station time-dependent data. (3) Alluvium creep properties: considerable difference are shown in calculated time-constants between results of small-scale dilatometer tests and large-scale estimates based on room-and-pillar time-dependent deformation measured over several months. (4) Rock load pressure cells data: these were obtained during the mine-by of a drift extension connecting the two shafts. These show load -transfer distances evolving with time. (5) Rock bolt information: load cell data and pullout test results. (6) Details of the ground support design. (7) Results of the three-dimensional modeling of the Ula complex with a boundary element code to evaluate the potential impact of two different schemes for future mining. (8) Plans for future rock mechanics studies. The lessons of this project can provide useful guidance to underground operations in weak, creeping ground.« less
  • In this paper, we present progress made in a study aimed atincreasing the understanding of the relative contributions of differentmechanisms that may be causing the seismicity occurring at The Geysersgeothermal field, California. The approach we take is to integrate: (1)coupled reservoir geomechanical numerical modeling, (2) data fromrecently upgraded and expanded NCPA/Calpine/LBNL seismic arrays, and (3)tens of years of archival InSAR data from monthly satellite passes. Wehave conducted a coupled reservoir geomechanical analysis to studypotential mechanisms induced by steam production. Our simulation resultscorroborate co-locations of hypocenter field observations of inducedseismicity and their correlation with steam production as reported in theliterature. Seismicmore » and InSAR data are being collected and processed foruse in constraining the coupled reservoir geomechanicalmodel.« less