Damage zone and slip-surface evolution over μm to km scales in high-porosity Navajo sandstone, Utah

2001 ◽  
Vol 23 (12) ◽  
pp. 1825-1844 ◽  
Author(s):  
Z.K. Shipton ◽  
P.A. Cowie
Keyword(s):  
Slip Surface ◽  
Damage Zone ◽  
High Porosity ◽  
Surface Evolution ◽  
Navajo Sandstone

Imaging damage zones and fault growth processes with high-precision relocations of earthquake sequences.

2021 ◽  
Author(s):  
Pierre Henry ◽  
Anthony Lomax ◽  
Sophie VIseur
Keyword(s):  
High Precision ◽  
Slip Surface ◽  
Shear Crack ◽  
Damage Zone ◽  
Normal Faulting ◽  
Multi Scale ◽  
Crack System ◽  
Stress Changes ◽  
Background Seismicity ◽  
Earthquake Sequences

<p>The architecture of fault damage zones combines various elements. Halos of intense fracturing forms around principal slip planes, possibly resulting from the shearing of slip surface rugosity or from dynamic stresses caused by earthquake ruptures. Splays forming off the tips and off the edges of a growing fault result in larger scale fracture networks and damage zones. Faults also grow by coalescence of en-echelon segments, such as Riedel fractures in a shear zone, and stress concentration at the steps results in linking damage zones. We show that these various elements of a shear-crack system can be recognized at seismogenic depth in earthquake sequences. Here we examine high-precision, absolute earthquake relocations for the Mw5.7 Magna UT, Mw6.4 Monte Cristo CA and Mw 5.8 Lone Pine CA earthquake sequences in 2020. We use iterative, source-specific, station corrections to loosely couple and improve event locations, and then waveform similarity between events as a measure for strongly coupling probabilistic event locations between multiplet events to greatly improve precision (see presentation EGU21-14608, and Lomax, 2020). The relocated seismicity shows mainly sparse clusters of seismicity, from which we infer multi-scale fault geometries. The uncertainty on earthquake locations (a few hundred meters) is typically larger than the width of halo damage zones observed in the field so that it is not possible to distinguish small aftershocks that could occur on a fracture within the halo or on a principal slip plane.</p><p>The relocated Magna seismicity shows a west-dipping, normal-faulting mainshock surface with an isolated, mainshock hypocenter at its base, surrounded up-dip in the hanging wall by a chevron of complex, clustered seismicity, likely related to secondary fault planes. This seismicity and a shallower up-dip cluster of aftershock seismicity correspond to clusters of background seismicity. The Lone Pine seismicity defines a main, east-dipping normal-faulting surface whose bottom edge connects to a steeper dipping splay, surrounded by a few clusters of background and reactivated seismicity. The space-time relation between background seismicity and multi-scale, foreshock-mainshock sequences are clearly imaged. The Monte Cristo Range seismicity (Lomax 2020) illuminates two, en-echelon primary faulting surfaces and surrounding, characteristic shear-crack features such as edge, wall, tip, and linking damage zones, showing that this sequence ruptured a complete shear crack system. In this example the width of the damage zone increases toward the earth surface.  Shallow damage zones align with areas of dense surface fracturing, subsidence and after-slip, showing the importance of damage zones for shaking intensity and earthquake hazard.</p><p>For all three sequences, some of the seismicity clusters delineate planar surfaces and concentrate along the edges of the suspected main slip patches. Other clusters of seismicity may result from larger scale damage associated with splay faults, en-echelon systems and linking zones, or with zones of background seismicity reactivated by stress changes from mainshock rupture. These types of seismicity and faulting structures may be more developed in the case of a complex rupture on an immature fault</p><p>__<br>Lomax (2020) The 2020 Mw6.5 Monte Cristo Range, Nevada earthquake: relocated seismicity shows rupture of a complete shear-crack system. https://eartharxiv.org/repository/view/1904</p>

scholarly journals A numerical sensitivity study of how permeability, geological structure, and hydraulic gradient control the lifetime of a geothermal reservoir

2019 ◽  
Author(s):  
Johanna F. Bauer ◽  
Michael Krumbholz ◽  
Elco Luijendijk ◽  
David C. Tanner
Keyword(s):  
Damage Zone ◽  
Complex Function ◽  
Sensitivity Study ◽  
Geological Structure ◽  
Hydraulic Gradient ◽  
High Porosity ◽  
High Permeability ◽  
Reservoir Volume ◽  
Thermal Breakthrough ◽  
High Yields

Abstract. Geothermal energy is an important and sustainable resource that has more potential than is currently utilized. Whether or not a deep geothermal resource can be exploited, depends on, besides temperature, mostly the utilizable reservoir volume over time, which in turn largely depends on petrophysical parameters. We show, using a large series (n = 1027) of 4-dimensional finite element models of a simple geothermal doublet, that the lifetime of a reservoir is a complex function of its geological parameters, their heterogeneity, and the background hydraulic gradient (BHG). In our models, we test the effects of porosity, permeability, and BHG in an isotropic medium. Further, we simulate the effect of permeability contrast and anisotropy induced by layering, fractures, and a fault. We quantify the lifetime of the reservoir by measuring the time to thermal breakthrough, i.e., how many years pass before the 100 °C isotherm (HDI) reaches the production well. Our results attest to the positive effect of high porosity; however, high permeability and BHG can combine to outperform the former. Certain configurations of all the parameters can cause either early thermal breakthrough or extreme longevity of the reservoir. For example, the presence of high permeability fractures, e.g., in a fault damage zone, can provide initially high yields, but channels fluid flow and therefore dramatically restricts the exploitable reservoir volume. We demonstrate that the magnitude and orientation of the BHG, provided permeability is sufficiently high, are prime parameters that affect the lifetime of a reservoir. Our numerical experiments show also that BHGs (low and high) can be outperformed by comparatively small variations in permeability contrast (103) and fracture-induced permeability anisotropy (101) that thus strongly affect the performance of geothermal reservoirs.

Periodic Fluid-mediated Weakening and Cementation Drives Cyclic Reorganisation of Shallow Basaltic Fault Zones

2021 ◽  
Author(s):  
Bob Bamberg ◽  
Richard Walker ◽  
Marc Reichow
Keyword(s):  
Host Rock ◽  
Slip Surface ◽  
Damage Zone ◽  
Fluid Pressure ◽  
Fault Zones ◽  
Fault Activity ◽  
Cyclic Activity ◽  
Fault Rock ◽  
Vein Formation ◽  
Rock Mechanical Properties

<p>Faults constitute the major source for mechanical and permeability heterogeneity in basaltic sequences, yet their architecture, and mechanical and physical properties remain poorly understood. These are however critical as basaltic reservoirs are becoming increasingly important for geothermal applications and CO<sub>2</sub> storage. Here we present a detailed microstructural- to outcrop-scale characterisation of mature (decametre-hectometre displacement) fault zones in layered basalts, in the Faroe Islands. Outcrop scale structures and fault rock distribution within the fault zone were mapped in the field to build 3D virtual outcrop models, with detailed characterisation of fault rock microstructure and petrology obtained from optical and SE-microscopy.</p><p>The fault zones exhibit evidence for cyclic activity controlled by fault internal fluid pressure variation. Deformation mechanisms in the core alternate between shear-compaction, evidenced by foliated cataclasite and gouge development, and dilatation through fluid overpressure, leading to hydrofracture and vein formation. Generally, a decametre-wide damage zone of Riedel faults is centrally transected by the fault core. The fault core is organised around a principal slip surface (PSS) hosted in a decimetre-wide principal slip zone (PSZ). The PSS and PSZ are dominantly composed of (ultra-) cataclasites, while the remaining core comprises anastomosing cataclastic bands bounding lenticular zones of various brecciated fault rocks. Further, PSS-proximal zones show significant late-stage dilatation by hydrothermal breccias or tabular veins with up to decimetre apertures, filled with early syntaxial to blocky zeolite and/or late coarse (≤ 1 cm) blocky calcite. The structures in the fault core are mutually overprinting, evidencing pulsed fault activity and PSS migration. The native plagioclase-pyroxene assemblage of the host rock is almost completely altered to zeolites and red-brown smectites in the fault core and along surrounding damage of mature faults, while lower displacement faults preserve the host rock mineralogy even in gouge. We infer that fluid flow along initial damage promotes alteration and the associated chemical weakening localises strain into a narrow PSZ. Here, fault activity is governed by alternating deformation styles – shear‑compaction and dilatation – suggesting changes in deformation mechanism linked to transient permeability decrease within the PSZ, followed by fluid overpressure and hydrofracture. Overall rock mechanical properties are thus governed by the combined effects of permanent chemical weakening and transient fluid-mediated mechanical weakening, alternating with cementation and healing, and will be explored by direct shear deformation experiments in the future.</p>

scholarly journals A numerical sensitivity study of how permeability, porosity, geological structure, and hydraulic gradient control the lifetime of a geothermal reservoir

Solid Earth ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 2115-2135 ◽  
Author(s):  
Johanna F. Bauer ◽  
Michael Krumbholz ◽  
Elco Luijendijk ◽  
David C. Tanner
Keyword(s):  
Damage Zone ◽  
Complex Function ◽  
Sensitivity Study ◽  
Geological Structure ◽  
Hydraulic Gradient ◽  
High Porosity ◽  
High Permeability ◽  
Reservoir Volume ◽  
Thermal Breakthrough ◽  
High Yields

Abstract. Geothermal energy is an important and sustainable resource that has more potential than is currently utilized. Whether or not a deep geothermal resource can be exploited, mostly depends on, besides temperature, the utilizable reservoir volume over time, which in turn largely depends on petrophysical parameters. We show, using over 1000 (n=1027) 4-D finite-element models of a simple geothermal doublet, that the lifetime of a reservoir is a complex function of its geological parameters, their heterogeneity, and the background hydraulic gradient (BHG). In our models, we test the effects of porosity, permeability, and BHG in an isotropic medium. Furthermore, we simulate the effect of permeability contrast and anisotropy induced by layering, fractures, and a fault. We quantify the lifetime of the reservoir by measuring the time to thermal breakthrough, i.e. how many years pass before the temperature of the produced fluid falls below the 100 ∘C threshold. The results of our sensitivity study attest to the positive effect of high porosity; however, high permeability and BHG can combine to outperform the former. Particular configurations of all the parameters can cause either early thermal breakthrough or extreme longevity of the reservoir. For example, the presence of high-permeability fractures, e.g. in a fault damage zone, can provide initially high yields, but it channels fluid flow and therefore dramatically restricts the exploitable reservoir volume. We demonstrate that the magnitude and orientation of the BHG, provided permeability is sufficiently high, are the prime parameters that affect the lifetime of a reservoir. Our numerical experiments show also that BHGs (low and high) can be outperformed by comparatively small variations in permeability contrast (103) and fracture-induced permeability anisotropy (101) that thus strongly affect the performance of geothermal reservoirs.

Permeability of carbonate fault rocks: a case study from Malta

2019 ◽  
Vol 26 (3) ◽  
pp. 418-433 ◽  
Author(s):  
Andy P. Cooke ◽  
Quentin J. Fisher ◽  
Emma A. H. Michie ◽  
Graham Yielding
Keyword(s):  
Fluid Flow ◽  
Host Rock ◽  
Damage Zone ◽  
Fault Zones ◽  
High Porosity ◽  
Rock Permeability ◽  
Fault Rock ◽  
Fault Rocks ◽  
Diagenetic Alteration ◽  
Hydraulic Behaviour

The inherent heterogeneity of carbonate rocks suggests that carbonate-hosted fault zones are also likely to be heterogeneous. Coupled with a lack of host–fault petrophysical relationships, this makes the hydraulic behaviour of carbonate-hosted fault zones difficult to predict. Here we investigate the link between host rock and fault rock porosity, permeability and texture, by presenting data from series of host rock, damage zone and fault rock samples from normally faulted, shallowly buried limestones from Malta. Core plug X-ray tomography indicates that texturally heterogeneous host rocks lead to greater variability in the porosity and permeability of fault rocks. Fault rocks derived from moderate- to high-porosity (>20%) formations experience permeability reductions of up to six orders of magnitude relative to the host; >30% of these fault rocks could act as baffles or barriers to fluid flow over production timescales. Fault rocks derived from lower-porosity (<20%) algal packstones have permeabilities that are lower than their hosts by up to three orders of magnitude, which is unlikely to impact fluid flow on production timescales. The variability of fault rock permeability is controlled by a number of factors, including the initial host rock texture and porosity, the magnitude of strain localization, and the extent of post-deformation diagenetic alteration. Fault displacement has no obvious control over fault rock permeability. The results enable better predictions of fault rock permeability in similar lithotypes and tectonic regimes. This may enable predictions of across-fault fluid flow potential when combined with data on fault zone architecture.

scholarly journals Scientific drilling and downhole fluid sampling of a natural CO<sub>2</sub> reservoir, Green River, Utah

2013 ◽  
Vol 16 ◽  
pp. 33-43 ◽  
Author(s):  
N. Kampman ◽  
A. Maskell ◽  
M. J. Bickle ◽  
J. P. Evans ◽  
M. Schaller ◽  
...  
Keyword(s):  
Fault Zone ◽  
Cold Water ◽  
Co2 Storage ◽  
Damage Zone ◽  
Normal Faults ◽  
Charged Fluids ◽  
Green River ◽  
Near Surface ◽  
Navajo Sandstone ◽  
Fluid Sampling

Abstract. A scientific borehole, CO2W55, was drilled into an onshore anticline, near the town of Green River, Utah for the purposes of studying a series of natural CO2 reservoirs. The objective of this research project is to recover core and fluids from natural CO2 accumulations in order to study and understand the long-term consequences of exposure of supercritical CO2, CO2-gas and CO2-charged fluids on geological materials. This will improve our ability to predict the security of future geological CO2 storage sites and the behaviour of CO2 during migration through the overburden. The Green River anticline is thought to contain supercritical reservoirs of CO2 in Permian sandstone and Mississippian-Pennsylvanian carbonate and evaporite formations at depths > 800 m. Migration of CO2 and CO2-charged brine from these deep formations, through the damage zone of two major normal faults in the overburden, feeds a stacked series of shallow reservoirs in Jurassic sandstones from 500 m depth to near surface. The drill-hole was spudded into the footwall of the Little Grand Wash normal fault at the apex of the Green River anticline, near the site of Crystal Geyser, a CO2-driven cold water geyser. The hole was drilled using a CS4002 Truck Mounted Core Drill to a total depth of 322 m and DOSECC’s hybrid coring system was used to continuously recover core. CO2-charged fluids were first encountered at ~ 35 m depth, in the basal sandstones of the Entrada Sandstone, which is open to surface, the fluids being effectively sealed by thin siltstone layers within the sandstone unit. The well penetrated a ~ 17 m thick fault zone within the Carmel Formation, the footwall damage zone of which hosted CO2-charged fluids in open fractures. CO2-rich fluids were encountered throughout the thickness of the Navajo Sandstone. The originally red sandstone and siltstone units, where they are in contact with the CO2-charged fluids, have been bleached by dissolution of hematite grain coatings. Fluid samples were collected from the Navajo Sandstone at formation pressures using a positive displacement wireline sampler, and fluid CO2 content and pH were measured at surface using high pressure apparatus. The results from the fluid sampling show that the Navajo Sandstone is being fed by active inflow of CO2-saturated brines through the fault damage zone; that these brines mix with meteoric fluid flowing laterally into the fault zone; and that the downhole fluid sampling whilst drilling successfully captures this dynamic process.

scholarly journals Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 2. Characterization of Fault Gouge from Deep Drilling and Implications for Fault Maturity

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 393 ◽  
Author(s):  
Li-Wei Kuo ◽  
Jyh-Rou Huang ◽  
Jiann-Neng Fang ◽  
Jialiang Si ◽  
Sheng-Rong Song ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Fault Zone ◽  
Active Fault ◽  
Slip Surface ◽  
Frictional Heating ◽  
Damage Zone ◽  
Temperature Perturbation ◽  
Carbonaceous Materials ◽  
Longmenshan Fault ◽  
Fault Belt

In recent works on the determination of graphitization of carbonaceous materials (CM) within the principal slip zone (PSZ) of the Longmenshan fault (China), we demonstrated that the formation of graphite, resulted from strain and frictional heating, could be evidence of past seismic slip. Here we utilize Raman Spectroscopy of CM (RSCM) on the CM-bearing gouges in the fault zone of the Longmenshan fault belt, at the borehole depth of 760 m (FZ760) from the Wenchuan earthquake Fault Scientific Drilling project-1 (WFSD-1), to quantitatively characterize CM and further retrieve ancient fault deformation information in the active fault. RSCM shows that graphitization of CM is intense in the fault core with respect to the damage zone, with the graphitized carbon resembling those observed on experimentally formed graphite that was frictionally generated. Importantly, compared to the recognized active fault zone of the Longmenshan fault, the RSCM of measured CM-rich gouge shows a higher degree of graphitization, likely derived from high-temperature-perturbation faulting events. It implies that FZ760 accommodated numerous single-event displacement and/or at higher normal stresses and/or in the absence of pore fluid and/or along a more localized slip surface(s). Because graphite is a well-known lubricant, we surmise that the presence of the higher degree graphitized CM within FZ760 will reduce the fault strength and inefficiently accumulate tectonic stress during the seismic cycle at the current depth, and further infer a plausible mechanism for fault propagation at the borehole depth of 590 m during the Mw 7.9 Wenchuan earthquake.

Sign in / Sign up

Export Citation Format

Share Document