Estimating near‐surface fracture systems from seismic anisotropy using a combination of crosshole surveys, VSPs, and reverse VSPs

1991 ◽  
Author(s):  
Enru Liu ◽  
Stuart Crampin ◽  
John H. Queen
Keyword(s):  
Seismic Anisotropy ◽  
Surface Fracture ◽  
Near Surface ◽  
Fracture Systems

scholarly journals Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW

2020 ◽  
Vol 6 (28) ◽  
pp. eabb0476
Author(s):  
Jorge C. Castellanos ◽  
Jonathan Perry-Houts ◽  
Robert W. Clayton ◽  
YoungHee Kim ◽  
A. Christian Stanciu ◽  
...  
Keyword(s):  
Pacific Northwest ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Azimuthal Anisotropy ◽  
Mantle Flow ◽  
Near Surface ◽  
Vertical Loading ◽  
The Pacific ◽  
Anisotropy Model ◽  
Lithosphere Dynamics

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

Shear‐wave splitting in cross‐hole surveys: Modeling

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Enru Liu ◽  
Stuart Crampin ◽  
David C. Booth
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Pore Space ◽  
Shear Waves ◽  
Shear Wave Splitting ◽  
Surface Layers ◽  
Near Surface ◽  
Crustal Rocks ◽  
Wave Splitting ◽  
Almost All

Shear‐wave splitting, diagnostic of some form of effective seismic anisotropy, is observed along almost all near‐vertical raypaths through the crust. The splitting is caused by propagation through distributions of stress‐aligned vertical parallel fluid‐filled cracks, microcracks, and preferentially oriented pore space that exist in most crustal rocks. Shear waves have severe interactions with the free surface and may be seriously disturbed by the surface and by near‐surface layers. In principle, cross‐hole surveys (CHSs) should be free of much of the near‐surface interference and could be used for investigating shear waves at higher frequencies and greater resolution along shorter raypaths than is possible with reflection surveys and VSPs. Synthetic seismograms are examined to estimate the effects of vertical cracks on the behavior of shear waves in CHS experiments. The azimuth of the CHS section relative to the strike of the cracks is crucial to the amount of information about seismic anisotropy that can be extracted from such surveys. Interpretation of data from only a few boreholes located at azimuths chosen from other considerations is likely to be difficult and inconclusive. Application to interpreting acoustic events generated by hydraulic pumping is likely to be more successful.

Fracture Distribution and Occurrence of DNAPL in a Clayey Lodgement Till

1999 ◽  
Vol 30 (4-5) ◽  
pp. 285-300 ◽  
Author(s):  
Peter Roll Jakobsen ◽  
Knud Erik S. Klint
Keyword(s):  
Preferential Flow ◽  
Surface Sediments ◽  
Coal Tar ◽  
Fracture Network ◽  
Field Investigation ◽  
Horizontal Shear ◽  
Near Surface ◽  
Migration Pathway ◽  
Fracture Systems ◽  
Fracture Distribution

This study examines the spatial fracture network in a clayey lodgement till, and the preferential flow pattern of DNAPL in the till. The study was conducted on a former gasworks site contaminated with coal tar. Fracture analysis was carried out and four fracture systems were recognised. Apart from fractures, burrows and root channels were recorded in the near surface sediments. Field investigation shows that two fracture systems were formed subglacially by loading of a glacier and horizontal shear within the lodgement till. Two other fracture systems were formed subsequently by desiccation and unloading/freeze-thaw processes in the unsaturated zone. Spatial distribution of free-phase DNAPL in the lodgement till is controled by the fracture network. The migration path of the DNAPL through the fracture systems is predominantly vertical in the upper 2 m and horizontal between 2 and 3.5 m. b.s. Below this depth the migration pathway is vertical. DNAPL was visually observed to a depth of 9 m.b.s. within fractures which continued downwards to unknown depth. Upscaling of the fracture properties was performed and a regional fracture model is suggested as a tool in future remidiation.

scholarly journals Natural fracture propping and earthquake-induced oil migration in fractured basement reservoirs

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 700-704 ◽  
Author(s):  
R.E. Holdsworth ◽  
K.J.W. McCaffrey ◽  
E. Dempsey ◽  
N.M.W. Roberts ◽  
K. Hardman ◽  
...  
Keyword(s):  
Source Rocks ◽  
Natural Fracture ◽  
Silica Gels ◽  
Near Surface ◽  
Oil Migration ◽  
Geological Processes ◽  
Fracture Systems ◽  
Basement Faults ◽  
Clastic Sediments ◽  
Basement Reservoirs

Abstract The geological processes that create fluid storage capacity and connectivity in global fractured basement reservoirs are poorly understood compared to conventional hydrocarbon plays. Hosting potentially multibillion barrels of oil, the upfaulted Precambrian basement of the Rona Ridge, offshore west of Shetland, UK, gives key insights into how such reservoirs form. Oil presence is everywhere associated with sub-millimeter- to meter-thickness mineralized fracture systems cutting both basement and local preseal cover sequences. Mineral textures and fluid inclusion geothermometry suggest a low-temperature (90–220 °C), near-surface hydrothermal system, as does the preservation of clastic sediments in the same fractures. These fills act as permanent props holding fractures open, forming long-term fissures in the basement that permit oil ingress and storage. Calcite-fill U-Pb dating constrains the onset of mineralization and contemporaneous oil charge to the Late Cretaceous. The additional preservation of oil-stained injected sediment slurries and silica gels along basement faults suggests that rift-related seismogenic faulting initiated lateral oil migration from Jurassic source rocks into the adjacent upfaulted ridge. Subsidence below sea level in the latest Cretaceous sealed the ridge with shales, and buoyancy-driven migration of oil into the preexisting propped fracture systems continued long after the cessation of rifting. These new observations provide an explanation for the viability of sub-unconformity fractured basement reservoirs worldwide, and have wider implications for subsurface fluid migration processes generally.

scholarly journals Passive seismic experiment “AniMaLS” in the Polish Sudetes (NE Variscides)

2021 ◽  
Vol 10 (2) ◽  
pp. 183-202
Author(s):  
Monika Bociarska ◽  
Julia Rewers ◽  
Dariusz Wójcik ◽  
Weronika Materkowska ◽  
Piotr Środa ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Geological Structure ◽  
Seismic Network ◽  
Data Quality Control ◽  
Crust And Upper Mantle ◽  
Near Surface ◽  
Correct Orientation ◽  
Seismic Experiment ◽  
Upper Mantle Structure ◽  
Passive Seismic

Abstract. The paper presents information about the seismic experiment “AniMaLS” which aims to provide a new insight into the crust and upper mantle structure beneath the Polish Sudetes (NE margin of the Variscan orogen). The seismic network composed of 23 temporary broadband stations was operated continuously for about 2 years (October 2017 to October 2019). The dataset was complemented by records from eight permanent stations located in the study area and in the vicinity. The stations were deployed with an inter-station spacing of approximately 25–30 km. As a result, recordings of local, regional and teleseismic events were obtained. We describe the aims and motivation of the project, the station deployment procedure, as well as the characteristics of the temporary seismic network and of the permanent stations. Furthermore, this paper includes a description of important issues like data transmission setup, status monitoring systems, data quality control, near-surface geological structure beneath stations and related site effects, etc. Special attention was paid to verification of correct orientation of the sensors. The obtained dataset will be analysed using several seismic interpretation methods, including analysis of seismic anisotropy parameters, with the objective of extending knowledge about the lithospheric and sublithospheric structure and the tectonic evolution of the study area.

Processing of a nine‐component near‐offset VSP for seismic anisotropy

Geophysics ◽  
1997 ◽  
Vol 62 (2) ◽  
pp. 676-689 ◽  
Author(s):  
Colin MacBeth ◽  
Xiang‐Yang Li ◽  
Xinwu Zeng ◽  
Dale Cox ◽  
John Queen
Keyword(s):  
Wave Field ◽  
Seismic Anisotropy ◽  
Similarity Transformation ◽  
Seismic Profile ◽  
Test Facility ◽  
Near Surface ◽  
Common Reference ◽  
Wave Field Separation ◽  
Matrix Operators ◽  
Field Separation

A convolutional sequence of matrix operators is offered as a convenient deterministic scheme for processing a multicomponent vertical seismic profile (VSP). This sequence is applied to a nine‐component near‐offset VSP recorded at the Conoco borehole test facility, Kay County, Oklahoma. These data are corrected for tool spin and near‐surface anisotropy together with source coupling or imbalance. After wave‐field separation using a standard f‐k filter, each source and receiver pair for the upgoing waves is adjusted to a common reference depth using a matrix operator based on the downgoing wave‐field. The up‐ and downgoing waves are then processed for anisotropy by a similarity transformation, to separate the [Formula: see text] and [Formula: see text] waves, from which the anisotropic properties are estimated. These estimates reveal a strong (apparent) vertical birefringence in the near‐surface, but weak or moderate values for the majority of the subsurface. The target zone consists of a thin sandstone and deeper shale layer, both of which possess a strong vertical birefringence. The sandstone corresponds to a zone of known fluid flow. An observed [Formula: see text] attenuation and polarization change in the shale suggest it contains large fractures.

Strong near-surface seismic anisotropy of Taiwan revealed by coda interferometry

2017 ◽  
Vol 475 ◽  
pp. 224-230 ◽  
Author(s):  
Li-Wei Chen ◽  
Ying-Nien Chen ◽  
Yuancheng Gung ◽  
Jian-Cheng Lee ◽  
Wen-Tzong Liang
Keyword(s):  
Seismic Anisotropy ◽  
Near Surface
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