Abstracts with Programs - Geological Society of America

SESSION NO. 28
has been sheared during shock compression and from which short, parallel lamellae emanate
in one direction, typically at an angle of 50-60°. Analysis of multiple sets of FFs in natural
samples shows that all FF lamellae within a sample trend in roughly the same direction, while
the sheared PFs form conjugate sets at ~90° angles. The principal axis of stress of the shock
wave is therefore assumed to lie at a 45° angle to the conjugate sets and parallel to the FF
lamellae. Thus FFs can be used as indicators for the orientation of differential stress within the
shock wave.
Although the generation of FFs as a shear-induced structure is clear in principle, details
of their formation are not yet completely understood. Specifically, the quartz grain’s lattice is
commonly distorted near the shear fracture, visible as an undulatory extinction pattern under
the microscope. In conventional structural geology, the orientation of this lattice distortion forms
as the result of “dragging” of material along the shear plane. Surprisingly, FFs show the exact
opposite orientation.
EBSD measurements are currently being performed on FFs to analyze lattice deformation
at a high resolution. Based on these initial results, we suggest that lattice deformation along
the PF is caused by elastic lattice strain accumulated during shearing in the shock wave,
which is then rapidly released during unloading, resulting in the opening of the FF lamellae
as extensional fractures (mode I) while rotating the lattice between two individual lamellae,
causing additional mode II in-plane shear along the lamellae and resulting in a distortion
pattern visible in EBSD measurements. Preliminary TEM analyses show that the junctions of
the FF lamellae with the PF are filled with vesicular amorphous material. Further EBSD and
TEM work is planned to give more detailed insights into the kinematics of dynamic fracturing
and shearing. A deeper understanding of this process can potentially be used to constrain
and differentiate fracturing mechanisms in shock waves from fracturing in lower-dynamic,
tectonic regimes.
28-6 BTH 6 Grokhovsky, Victor
THE FAILURE OF METEORITES IN IMPACT TESTS: THE EFFECT OF STRUCTURE AND
TEMPERATURE
GROKHOVSKY, Victor1 , GLADKOVSKY, Sergey2 , KOZLOVSKIKH, Ekaterina1 ,
and PYATKOV, Anton1 , (1) Physico-Technical, Ural Federal University, Mira St, 19,
Ekaterinburg, 620002, Russia, grokh47@mail.ru, (2) Institute of Engineering Science of
the Ural Branch of RAS, Ekaterinburg, 620219, Russia
There are few data about mechanical properties and behavior of meteoroids under shock load,
yet these properties are crucial to understanding how to deal with asteroidal and cometary
threat. In addition meteoroids were loaded dynamically during mutual impact action, interaction
with atmosphere and earth surface. However, previously the majority of strength data were
obtained from compressive tests while only few experimental results in this field were related
to tensile tests. In this work we present the numerical results on impact strength and crack
propagation resistance of both different meteoritic materials and ice.
Dynamic tests were performed using instrumented Tinius Olsen IT542 impact test machine
at 300–77 K. Samples were prepared from monocrystalline and polycrystalline fragments of
octahedrite Sikhote-Alin IIAB, impact-reheated meteorite Dronino (Iron-ung), ataxite Chinga
IVB, chondrite Tsarev L5 and ice. SEM JEOL JSM-66490LV and TESCAN VEGA were used for
fracture surface analysis of studied fragments. The SEM pictures were quantitatively processed
using image analysis system SIAMS 700.
The highest values of impact strength (2210 kJ/m2 and 2070 kJ/m2 ) and maximum of
crack propagation energy were obtained for Chinga and Dronino iron meteorites which had
submicroscopical (α+α +γ) and duplex (α+α ) structures, respectively. Decrease of the test
2 2
temperature down to 77 K led to decrease of impact strength values down to 47 kJ/m2 for
Dronino and 1170 kJ/m2 for Chinga meteorites. Monocrystalline Sikhote-Alin meteorite samples
demonstrated brittle transcrystalline fracture surface mode while polycrystalline Sikhote-Alin
samples were characterized by intercrystalline fracture mechanism. In this case fracture
energy was less than that for Tsarev L5 chondrite. The performed study clears up that the
process of meteoritic materials failure is strongly affected by their chemical composition, type
of microstructure and test temperature. It may be a result of different values of impact strength,
impact testing parameters (ratio of crack initiation, propagation and total fracture energy) along
the side with fracture mechanism transfer from ductile to brittle transcrystalline mode. This work
was supported in part by the RFBR grant No 10-05-96047-r-ural-à.
SESSION NO. 29, 08:30
Tuesday, 6 September 2011
T3D. Induced Seismicity – From Observation to
Geomechanical Understanding (Posters)
Ludwig-Maximilians-Universität München,
Poster Hall P1 (E110, Senatsraum, 1st floor)
29-1 BTH 27 Chernyavski, Vladimir M.
MODELING OF THE TEMPORAL EVOLUTION OF EFFECTIVE STRESS, PORE PRESSURE,
COMPACTION, FILTRATION, AND GROWING OF GAS HYDRATES IN THE CASE OF
THE SEQUENTIAL ACCUMULATION OF SEDIMENTARY LAYERS WITH DIFFERENT
RHEOLOGICAL PROPERTIES
CHERNYAVSKI, Vladimir M., Institute of Mechanics, Lomonosov Moscow State University,
Michurinskii pr. 1, Moscow, 119192, Russia, vcherniavski@gmail.com and SUETNOVA,
Elena I., Institute of Physics of the Earth, Russian Academy of Sciences, B. Gruzinskaya
10, IFZ, Moscow, 123995, Russia
The processes of the evolutions of the effective stress, compaction, and fluid and gas filtrations
in the permeable sedimentary rocks during their sequential accumulation are described in the
frame of a poro-visco-elastic (Maxwell-type) constitutive law. But such a process is disturbed
by the precipitation and accumulations of a species in its P-T stability zones. This processes
lead to decreasing of porosity and permeability. Mathematical model of coupled processes
of sediment compaction, pore fluid and gas migration and pore feeling by precipitation is
developed.
Mathematical formulation of physical problem of low-viscosity fluid- gas flow in a deformable
poro-visco-elastic matrix with moving boundary consists of the system of nonlinear partial
differential equations with appropriate boundary conditions. Because the permeability
nonlinearly depends upon porosity, and the effective pressure gradient is interrelated with
deformation of sediment matrix under the loading, the dynamic of fluid is controlled by the
behavior of deformable matrix.
Calculations with parameters that are within the framework of the available geophysical data
show that the accumulation of sedimentary layers with a permeability or viscosity differing from
that of the main basin fill leads with time to the formation, deep within the basin, of layers that
have a higher porosity and a different overhydrostatic pore pressure as compared with the
surrounding layers. The lower-viscosity layer of sediment is compacted more rapidly, thereby
creating an obstacle for the pore fluid and gas motion toward the surface. Subsequently, as the
A42 FRAGILE EARTH: Geological Processes from Global to Local Scales
overlying sedimentary layers accumulate, the compaction process leads to the formation of two
zones above and below the lower-viscosity layer, in each of which the porosity decrease with
increasing depth becomes more pronounced with time. The pore pressure in the lower zone
increases more rapidly than in the upper one due to a rapid porosity decrease in the lowerviscosity
layer. On model examples shown as a sequential accumulation of porous sediments
with different viscosity quantitatively affects on the evolution and contemporary values of
effective stress, pore pressure, fluid and gas filtration and accumulation of gas hydrates in
the pores.
29-2 BTH 28 Eckert, Andreas
CO2 INJECTION IN ANTICLINE RESERVOIRS: STRUCTURAL INFLUENCES ON MAXIMUM
SUSTAINABLE PORE PRESSURE AND SEISMICITY RELATED TO FAULT REACTIVATION
ECKERT, Andreas, PARADEIS, Matthew, and AMIRLATIFI, Amin, Petroleum Engineering,
Missouri University of Science and Technology, Rolla, MO 65409, eckertan@mst.edu
Anticline structures are one of the most common structural traps for hydrocarbon reservoirs
and are thus becoming prime targets for geologic CO sequestration into saline formations.
2
The injection of CO into geologic formations increases the formation pore pressure and
2
induces geomechanical risks such as fracture reactivation or the generation of new fractures.
This will result in seismicity and lastly generate preferred fluid flow pathways along which
dissolved CO may escape into the atmosphere. In order to assess these geomechanical risks
2
a thorough simulation coupling fluid flow through porous media and geomechanics of a realistic
representation of the formation of interest is required.
In this study we use a one-way coupling approach transferring pore pressure results
from a reservoir simulator to geomechanical models using finite element analysis. From
the mechanical finite element models, we initially determine the maximum sustainable pore
pressure before CO injection. Our geomechanical models show that structural parameters
2
such as anticline amplitude and wavelength, layer thickness and intra-bedding friction under
various stress regimes have a significant impact on the maximum sustainable pore pressure in
the reservoir.
After injection we study the spatial and temporal CO plume evolution in the reservoir
2
and transfer the resulting pore pressures back to the geomechanical models. We include a
preferably oriented fault in the model and propose 2 procedures to simulate fault reactivation.
Our models show that CO induced pore pressure increase can trigger reactivation of pre-
2
existing structures and based on the resulting fault slip the resulting seismic magnitudes can
be estimated.
29-3 BTH 29 López, Allan
TRIGGERED SEISMICITY EXPECTED IN HYDROELECTRIC RESERVOIRS CLOSE TO THE
SUBDUCTION ZONE IN COSTA RICA
LÓPEZ, Allan, Engineering Geology, I.C.E, UEN PYSA, Sabana Norte, San Josè 1000
Costa Rica, alopezs@ice.go.cr
The tectonic stress field imparted by the subducting Cocos plate on the Caribbean plate along
the central pacific region in southern Costa Rica and the changes in the associated fluid
pressure and friction during impoundment and drawdown of hydropower reservoirs, determine
the reactivation of faults and pre-existing discontinuities and the formation of new ones. The
geomechanical attributes of the present day stress field, the rockmass properties and the ways
in which they are combined according to the local and regional geological structure, lithology
and rock matrix in association with the prevailing tectonic regimes, control the likelihood of
fault reactivation. Some variables such as impoundment-drawdown rates and speeds can be
modified, but it can not be done for the subduction related and background seismicity. In this
context adequate modeling of the reactivation must take into consideration the stress and fluid
pressures required to start the hydrofracturing, opening and sliping of faults networks.
In one of the analyzed cases in a reservoir with a maximum depth of 162 meters in Tertiary
turbidites crosscrossed by NW dextral active faults and reverse NWW structures within a stress
field with a subhorizontal σ trending towards N22°E, the hydrofracturing must be at least 9.
1
02652e + 006 Pa to start and 4. 82652e + 006 Pa to open the existing faults. The Slip Tendency
analysis indicates that only the reverse faults dipping less than 15 ° are prone to reactivate
under the stated conditions while the dextral shears shall move when their strikes are in the
range of N40°W to N10°E. The sensitivity of these variables in a scenario with a major seismic
event has been shaped by a Coulomb Stress Failure modeling, which indicated that the stress
transfer induced by a maximum credible Mw 6,5 earthquake with inverse geometry and 30%
of dextral component would not increase the seismic hazard at any depth in the area of direct
influence of the reservoir.
29-4 BTH 30 Haghi, Amir Hossein
EVALUATION AND ANALYSIS OF RESERVOIR FLUID FLOW EFFECT ON FIELD
STRESS; A NEW APPROACH TO ALLEVIATE INDUCED SEISMICITY IN HYDROCARBON
RESERVOIRS
HAGHI, Amir Hossein, Research Center of Petroleum University of Technology, Tehran,
1453953153, Iran, amirh886@yahoo.com, KHARRAT, Riyaz, Petroleum University
of Technology, Tehran, 1453953153, Iran, and ASEF, M.R., Geology, Tarbiat Moalem
University, Tehran, 1453953153, Iran
Annually, natural and artificial earthquakes cause irreparable damages for human communities.
Induced seismicity which refers to human-made shocks and tremors that alters the stresses
state on the Earth’s crust, invigorates in form of hydrocarbon reservoir-induced seismic that is
related to operations with changing reservoir stress states. As it is provided in many references
and research projects, reservoir stress field is a strong function of reservoir pore pressure.
Hence long term production and injection scenarios or stimulation activities influence the stress
state of reservoir based on time and place in the reservoir span.
Among all indicated parameters including long term production-injection operations,
stimulation, and reservoir pressure variations in time and place, there is another key parameter
named fluid flow rate which could be controlled by us to calm down stress disruption and thus
alleviate induced seismicity magnitude in hydrocarbon reservoirs. During reservoir stimulation,
long term production- injection, the only parameter which is altered dramatically and caused
some hazards is the fluid flow rate in the well and all situations in reservoir. Reservoir pressure
is a strong function of fluid flow rate and thus filed stress could be formulized based on that in
reservoir as well.
In this approach using diffusivity equation in reservoir space and solving it with analytical and
numerical methods, reservoir pressure is related to fluid flow in all distance from the producing
well to reservoir boundary for all times steps. Accordingly, reservoir stress state could be
formulated based on production flow rates. During single or multi wall production, sensitive
locations around the flowing wells have the biggest chance for induced seismicity. Regarding
that flow rate is the only attainable tool in order to control the intensity of stress confliction,
this method proves numerically “How much dividing the producing fluid flow into several ways
will lessen the chance of stress confliction and induced seismicity in Hydrocarbon Reservoir
Spaces”.
The accuracy of this method is confirmed using production data and numerical models of two
giant hydrocarbon fields located in western section of Persian Gulf, Southern Iran.