Validating the origin of microseismic events in target reservoir using guided waves recorded by DAS

2020 ◽  
Vol 39 (11) ◽  
pp. 776-784
Author(s):  
Owen Huff ◽  
Ariel Lellouch ◽  
Bin Luo ◽  
Ge Jin ◽  
Biondo Biondi
Keyword(s):  
Wave Energy ◽  
Guided Waves ◽  
Velocity Structure ◽  
Guided Wave ◽  
Accurate Estimation ◽  
Low Velocity ◽  
Eagle Ford ◽  
Low Velocity Layer ◽  
Microseismic Events ◽  
Velocity Layer

We develop a new algorithm that uses guided-wave energy in distributed acoustic sensing (DAS) records to identify microseismic events originating within or very close to a shale reservoir. Guided waves are dispersive waves that propagate in a low-velocity layer bounded by two high-velocity layers. This is a geologic structure that is seen for some shale reservoirs, most notably the Eagle Ford. Only microseismic events originating within or close to the low-velocity layer will excite significant guided-wave energy, which can be observed in DAS records. We confirm the relationship between guided-wave energy and event depth relative to the reservoir by using synthetic modeling. Given the known velocity structure, we can predict the dispersion curves for guided waves and use them to separate body and guided waves. We demonstrate a method to quantify the amplitude of guided waves in field DAS data recorded directly above the Eagle Ford Shale. Using this technique, we can separate events that originate within or close to the Eagle Ford from events that do not, thus circumventing the large depth uncertainty in a microseismic catalog derived from surface geophones. Our analysis shows that events classified as originating within or close to the Eagle Ford are horizontally closer to the stimulating well than non-Eagle Ford events. This is interpreted as representing different hydraulic fracture geometries in the Eagle Ford compared to its bounding formations, the Buda Limestone and Austin Chalk. The application of our method yields a new catalog that highlights the events relevant to stimulation and production in the target reservoir. It also provides a strong depth constraint that can improve relocation attempts using surface data, enabling a more accurate estimation of stimulated rock volume geometry.

An eigenfunction representation of deep waveguides with application to unconventional reservoirs

Geophysics ◽  
2021 ◽  
Vol 86 (6) ◽  
pp. T509-T521
Author(s):  
Owen Huff ◽  
Bin Luo ◽  
Ariel Lellouch ◽  
Ge Jin
Keyword(s):  
Finite Difference ◽  
Energy Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Guided Waves ◽  
Guided Wave ◽  
Low Velocity ◽  
Eagle Ford ◽  
Low Velocity Zone ◽  
Velocity Zone

Guided waves that propagate in deep low-velocity zones can be described using the displacement-stress eigenfunction theory. For a layered subsurface, these eigenfunctions provide a framework to calculate guided-wave properties at a fraction of the time required for fully numerical approaches for wave-equation modeling, such as the finite-difference approach. Using a 1D velocity model representing the low-velocity Eagle Ford Shale, an unconventional hydrocarbon reservoir, we verify the accuracy of the displacement eigenfunctions by comparing with finite-difference modeling. We use the amplitude portion of the Green’s function for source-receiver eigenfunction pairs as a proxy for expected guided-wave amplitude. These response functions are used to investigate the impact of the velocity contrast, reservoir thickness, and receiver depth on guided-wave amplitudes for discrete frequencies. We find that receivers located within the low-velocity zone record larger guided-wave amplitudes. This property may be used to infer the location of the recording array in relation to the low-velocity reservoir. We also study guided-wave energy distribution between the different layers of the Eagle Ford model and find that most of the high-frequency energy is confined to the low-velocity reservoir. We corroborate this measurement with field microseismic data recorded by distributed acoustic sensing fiber installed outside of the Eagle Ford. The data contain high-frequency body-wave energy, but the guided waves are confined to low frequencies because the recording array is outside the waveguide. We also study the energy distribution between the fundamental and first guided-wave modes as a function of the frequency and source depth and find a nodal point in the first mode for source depths originating in the middle of the low-velocity zone, which we validate with the same field data. The varying modal energy distribution can provide useful constraints for microseismic event depth estimation.

Modeling fault‐zone guided waves of microearthquakes in a geothermal reservoir

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1278-1284 ◽  
Author(s):  
Min Lou ◽  
José A. Rial ◽  
P. E. Malin
Keyword(s):  
Fault Zone ◽  
Guided Waves ◽  
Velocity Structure ◽  
Geothermal Field ◽  
Guided Wave ◽  
S Wave ◽  
Low Velocity ◽  
Geothermal Fields ◽  
Coso Geothermal Field ◽  
Fault Zone Structures

Fault‐zone guided waves have been identified in microearthquake seismograms recorded at the Coso Geothermal Field, California. The observed guided waves have particle motions and propagation group velocities similar to Rayleigh wave modes. A numerical method has been employed to simulate the guided‐wave propagation through the fault zone. By comparing observed and synthetic waveforms the fault‐zone width and its P‐ and S‐wave velocity structure have been estimated. It is suggested here that the identification and modeling of such guided waves is an effective tool to locate fracture‐induced, low‐velocity fault‐zone structures in geothermal fields.

scholarly journals Pervasive low-velocity layer atop the 410-km discontinuity beneath the northwest Pacific subduction zone: Implications for rheology and geodynamics

2021 ◽  
Vol 554 ◽  
pp. 116642
Author(s):  
Guangjie Han ◽  
Juan Li ◽  
Guangrui Guo ◽  
Walter D. Mooney ◽  
Shun-ichiro Karato ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Northwest Pacific ◽  
Low Velocity ◽  
Low Velocity Layer ◽  
Velocity Layer

Focal mechanisms of earthquakes related to the 29 November 1975 Kalapana, Hawaii, earthquake: The effect of structure models

1981 ◽  
Vol 71 (3) ◽  
pp. 713-729 ◽  
Author(s):  
R. S. Crosson ◽  
E. T. Endo
Keyword(s):  
Main Shock ◽  
Horizontal Layer ◽  
Focal Mechanisms ◽  
Local Network ◽  
The South ◽  
Low Velocity ◽  
Tectonic Model ◽  
Low Velocity Layer ◽  
Using Data ◽  
Velocity Layer

abstract Initial focal mechanism determinations for the 29 November 1975 Kalapana, Hawaii, earthquake indicated discrepancy between the mechanism determined from teleseismic data by Ando and the mechanism determined using data from the local U.S. Geological Survey network surrounding the epicenter region. The resolution of this difference is crucial to correctly understand this earthquake, as well as to understand the tectonics of the south flank of Kilauea volcano. When a model with a low-velocity layer at the base of the crust is used for projection back to the focal sphere for the local network mechanisms, the discrepancy vanishes. To further investigate this result, focal mechanisms were determined using several contrasting models for a set of well-recorded earthquakes. A large number of these earthquakes have mechanisms identical to the main shock when the low-velocity layer model is used. Dispersion of P and T axes is also minimized by use of this model. A low-angle slip direction, favored for the main shock and typical of most other solutions, exhibits remarkable stability normal to the east rift zone of Kilauea. Our results suggest a tectonic model, similar in nature to that proposed by Ando, in which the south flank of Kilauea consists of a mobile block of crust which is relatively free to move laterally on a low-strength zone at about 10 km depth. Forceful injection of magma along the rift zones provides the loading stress which is released by catastrophic failure in the weak, horizontal layer in a cycle of perhaps 100 yr.

Sea-floor evolution: rare-earth evidence

1971 ◽  
Vol 268 (1192) ◽  
pp. 663-706 ◽  
Keyword(s):  
Rare Earth ◽  
Mantle Source ◽  
Upper Mantle ◽  
Gulf Of Aden ◽  
Low Velocity ◽  
East Pacific ◽  
Mid Ocean Ridge ◽  
Low Velocity Layer ◽  
Ocean Ridge ◽  
Velocity Layer

A systematic survey of rare-earth (r.e.) abundances in submarine tholeiitic basalts along mid-oceanic ridges has been made by neutron activation analysis. The r.e. fractionation patterns are remarkably uniform along each mid-oceanic ridge and from one ridge to another (Juan de Fuca Ridge, East Pacific and Chile Rise, Pacific-Antarctic, Mid-Indian and Carlsberg Ridge, Gulf of Aden, Red Sea Trough and Reykjanes Ridge). The patterns are all depleted in light r.e. except for three samples (Gulf of Aden and Mid-Indian Ridge) which are unfractionated relative to chondrites. They contrast markedly with tholeiitic plateau basalt which are shown to be related to the early volcanic phases associated with continental drift. Tholeiitic plateau basalts are light r.e. enriched as are most continental rocks. Mid-ocean ridge basalts are also distinguishable from spatially related oceanic shield volcanoes of tholeiitic composition (Red Sea Trough-Jebel Teir Is., East Pacific Rise-Culpepper Island). Thus on a r.e. basis there are tholeiites within tholeiites. The r.e. difference between mid-ocean ridge tholeiites and tholeiitic plateau basalts can be related to distinct thermal and tectonic régimes and consequently magmatic modes and rates of intrusions from the low velocity layer in the upper mantle. The difference between continental and oceanic volcanism appears to be triggered by: (1) presence or absence of a moving continental lithosphere over the low velocity layer, and (2) whether or not major rifts tap the low velocity layer through the lithosphere. Fractional crystallization during ascent of melts before eruption at the ridge crest does not affect appreciably the relative r.e. patterns. R.e. in mid-ocean ridge basalts appear to intrinsically reflect their distribution in the upper mantle source, i.e. the low velocity layer. Based on secondary order r.e. variation of mid-ocean ridge basalts: (1) If fractional crystallization is invoked for the small r.e. variations, up to approximately 50 % extraction of olivine and Ca-poor orthopyroxene in various combinations can be tolerated. However, only limited amount of plagioclase or Ca-rich clinopyroxene can be extracted, the former because of its effect on the abundance of Eu abundance and the latter because of its effect on the [La/Sm] e.f. ratio, alternatively. (2) If partial melting during ascent is invoked, and a minimum of 10% melting is assumed, the permissible degree of melting of originally a lherzolite upper mantle may vary between 10 and 30% . It is not possible to establish readily to what extent these two processes have been operative as they cannot be distinguished on the basis of r.e. data only. However, there is evidence indicating that both have been operative and are responsible for the small r.e. variations observed in mid-ocean ridge basalts. An attempt to correlate second order r.e. variations along or across mid-oceanic ridges with spreading rate, age, or distance from ridge crests has been made but the results are inconclusive. No r.e. secular variation of the oceanic crust is apparent. R.e. average ridge to ridge variations are attributed to small lateral inhomogeneities of the source of basalts in the low velocity layer, and to a certain extent, to its past history. The remarkable r.e. uniformity of mid-oceanic ridge tholeiites requires a unique and simple volcanic process to be operative. It calls for upward migration of melt or slush from a relatively homogeneous source in the mantle—the low velocity layer, followed by further partial melting during ascent. The model, although consistent with geophysics, may have to be reconciled with some evidence from experimental petrology. Models for r.e. composition of the upper mantle source of ridge basalt, formation of layers 2 and 3, and the moho-discontinuity, are also presented.

scholarly journals Numerical and Experimental Investigation of Guided Wave Propagation in a Multi-Wire Cable

2019 ◽  
Vol 9 (5) ◽  
pp. 1028 ◽  
Author(s):  
Pengfei Zhang ◽  
Zhifeng Tang ◽  
Fuzai Lv ◽  
Keji Yang
Keyword(s):  
Wave Energy ◽  
Guided Waves ◽  
Wave Structure ◽  
Excitation Power ◽  
Dispersion Analysis ◽  
Guided Wave ◽  
Ultrasonic Guided Waves ◽  
Mechanical Coupling ◽  
Guided Wave Propagation ◽  
Contact Acoustic Nonlinearity

Ultrasonic guided waves (UGWs) have attracted attention in the nondestructive testing and structural health monitoring (SHM) of multi-wire cables. They offer such advantages as a single measurement, wide coverage of the acoustic field, and long-range propagation ability. However, the mechanical coupling of multi-wire structures complicates the propagation behaviors of guided waves and signal interpretation. In this paper, UGW propagation in these waveguides is investigated theoretically, numerically, and experimentally from the perspective of dispersion and wave structure, contact acoustic nonlinearity (CAN), and wave energy transfer. Although the performance of all possible propagating wave modes in a multi-wire cable at different frequencies could be obtained by dispersion analysis, it is ineffective to analyze the frequency behaviors of the wave signals of a certain mode, which could be analyzed using the CAN effect. The CAN phenomenon of two mechanically coupled wires in contact was observed, which was demonstrated by numerical guided wave simulation and experiments. Additionally, the measured guided wave energy of wires located in different layers of an aluminum conductor steel-reinforced cable accords with the theoretical prediction. The model of wave energy distribution in different layers of a cable also could be used to optimize the excitation power of transducers and determine the effective monitoring range of SHM.

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