Regional seismicity: A potential pitfall for identification of long-period long-duration events

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. A1-A5 ◽  
Author(s):  
Enrico Caffagni ◽  
David Eaton ◽  
Mirko van der Baan ◽  
Joshua P. Jones
Keyword(s):  
Treatment Programs ◽  
Gas Field ◽  
Similar Frequency ◽  
Regional Seismicity ◽  
Long Period ◽  
Long Duration ◽  
Deformation Processes ◽  
Using Data ◽  
Tight Sand Gas ◽  
Regional Earthquake

Long-period long-duration (LPLD) events are tremorlike signals that have been observed during monitoring of hydraulic-fracture treatment programs. LPLD events have been interpreted to reflect slow deformation processes on fractures or faults that are misoriented for reactivation with respect to the present-day stress field. Regional earthquakes could easily be mistaken for LPLD events because both are characterized by similar frequency content ([Formula: see text]) and duration ([Formula: see text]). Using data from a 10.5-month continuous downhole deployment of a 15-Hz geophone array in a tight-sand gas field in western Canada, we compared recordings of small earthquakes with previously published LPLD events. We determined that regional earthquakes can show similar waveform characteristics to LPLD events, underscoring the importance of distinguishing regional earthquake signals from LPLD events to ensure robust interpretation of reservoir deformation processes.

On the nature of long-period long-duration seismic events detected during hydraulic fracturing

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. KS113-KS121 ◽  
Author(s):  
Megan Zecevic ◽  
Guillaume Daniel ◽  
Dana Jurick
Keyword(s):  
Hydraulic Fracturing ◽  
Clay Content ◽  
Microseismic Monitoring ◽  
Seismic Events ◽  
Earthquake Catalog ◽  
Data Set ◽  
Long Period ◽  
Long Duration ◽  
Spatial Coverage ◽  
Using Data

Long-period long-duration (LPLD) seismic events are low-amplitude tremor-like seismic signals that have been observed in some microseismic monitoring data sets acquired during hydraulic fracturing operations. The LPLD events have been interpreted to be associated with slow slip along preexisting fractures presumed to either have high clay content or be misaligned with respect to the current-day principal stress directions. However, a recent study indicates that regional earthquakes, when recorded on vertical downhole monitoring arrays, have similar signal characteristics to LPLD events and that care must be taken when analyzing and interpreting such signals. Using data from a hydraulic fracturing microseismic data set in which LPLD events have previously been identified and well documented, together with data from the EarthScope Transportable USArray, we have investigated the hypothesis that the documented LPLD events were regional earthquakes. We have determined that the LPLD events corresponded with signals recorded on the USArray at distances of up to 350 km away from the injection well, although they were not listed in any regional earthquake catalog. The spatial coverage of the USArray allows the sources of many of the LPLD events to be relocated outside of the treatment well area and thus suggests that they are regional earthquakes of magnitude smaller than M2.5 rather than locally sourced events related to the hydraulic fracturing stimulation process.

Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery

2021 ◽  
Author(s):  
Charlotte Bruland ◽  
Sarah Mader ◽  
Céline Hadziioannou
Keyword(s):  
Spectral Analysis ◽  
Volcanic Activity ◽  
Rayleigh Waves ◽  
Spectral Characteristics ◽  
Gulf Of Guinea ◽  
Seismic Amplitude ◽  
Long Period ◽  
Amplitude Spectra ◽  
Using Data ◽  
Over Time

<p>In the 1960's a peak in the seismic amplitude spectra around 26 s was discovered and detected on stations worldwide. The source was located in the Gulf of Guinea, with approximate coordinates (0,0), and was believed to be generated continuously. A source with similar spectral characteristics was discovered near the Vanuatu Islands, at nearly the antipodal location of the Gulf of Guinea source. Since it was located close to the volcanoes in Vanuatu, this source is commonly attributed to magmatic processes. The physical cause of the 26 s microseism, however, remains unclear.</p><p>We investigate the source location and evolution of the 26 s microseim using data from permanent broadband stations in Germany, France and Algeria and temporary arrays in Morocco, Cameroon and Botswana for spectral analysis and 3-C beamforming to get closer to resolving the source mechanism responsible for this enigmatic signal. We find that the signal modulates over time and is not always detectable, but occasionally it becomes so energetic it can be observed on stations worldwide. Such a burst can last for hours or days. The signal is visible on stations globally approximately 30 percent of the time. Our beamforming analysis confirms that the source is located in the Gulf of Guinea, as shown in previous studies, and that the location is temporally stable. Whenever the signal is detectable, both Love and Rayleigh waves are generated. We discover a spectral glide effect associated with the bursts, that so far has not been reported in the literature. </p><p>The spectral glides last for about two days and are observed on stations globally. Although at higher frequencies, very long period tremors and gliding tremors are also observed on volcanoes as Redoubt in Alaska and Arenal in Costa Rica, suggesting that the origin of the 26 s tremor is also volcanic. However, there is no reported volcanic activity in the area where the source appears to be located.</p><p> </p>

scholarly journals Gender Differences in Neuropsychiatric Symptoms Among Community-Dwelling Mexican Americans Aged 80 and Older

2021 ◽  
Vol 36 ◽  
pp. 153331752110429
Author(s):  
Sadaf Arefi Milani ◽  
Phillip A Cantu ◽  
Abbey B. Berenson ◽  
Yong-Fang Kuo ◽  
Kyriakos S. Markides ◽  
...  
Keyword(s):  
Gender Differences ◽  
Mexican Americans ◽  
Neuropsychiatric Symptoms ◽  
The Elderly ◽  
Community Dwelling ◽  
Treatment Programs ◽  
Depression And Anxiety ◽  
Logistic Regression Models ◽  
Using Data ◽  
Design And Methods

Background and Objectives To assess gender differences in prevalence of neuropsychiatric symptoms (NPS) among community-dwelling Mexican Americans ≥80 years. Research Design and Methods: Using data from Wave 7 (2010–2011) of the Hispanic Established Population for the Epidemiological Study of the Elderly, we analyzed the NPS of 914 participants as determined by the Neuropsychiatric Inventory (NPI) with assessments conducted by their caregivers. Multivariate logistic regression models were used to test the association of individual NPS with gender, adjusting for relevant characteristics. Results: The average age of our sample was 86.1 years, and 65.3% were women. Over 60% of participants had at least one informant/caregiver reported NPS. After adjustment, women had lower odds than men of agitation/aggression but higher odds of dysphoria/depression and anxiety. Discussion: Recognizing gender differences in NPS phenotype could help guide development of culturally appropriate NPS screening and treatment programs.

scholarly journals Fluid pressure arrival-time tomography: Estimation and assessment in the presence of inequality constraints with an application to production at the Krechba field, Algeria

Geophysics ◽  
2010 ◽  
Vol 75 (6) ◽  
pp. O39-O55 ◽  
Author(s):  
Alessio Rucci ◽  
D. W. Vasco ◽  
Fabrizio Novali
Keyword(s):  
Surface Deformation ◽  
Transient Flow ◽  
Fluid Pressure ◽  
Inequality Constraints ◽  
Gas Production ◽  
Gas Field ◽  
Peak Displacement ◽  
Geomechanical Properties ◽  
Fluid Production ◽  
Using Data

Deformation in the overburden proves useful in deducing spatial and temporal changes in the volume of a producing reservoir. Based on these changes, we have estimated diffusive traveltimes associated with the transient flow due to production, and then, as the solution of a linear inverse problem, the effective permeability of the reservoir. An advantage of the approach based on traveltimes, as opposed to one based on the amplitude of surface deformation, is that it is much less sensitive to the exact geomechanical properties of the reservoir and overburden. Inequalities constrain the inversion, under the assumption that the fluid production only results in pore volume decreases within the reservoir. The formulation has been applied to satellite-based estimates of deformation in the material overlying a thin gas production zone at the Krechba field in Algeria. The peak displacement after three years of gas production is found to be approximately [Formula: see text], overlying the eastern margin of the anticlinal structure defining the gas field. Using data from 15 irregularly spaced images of range change, we have calculated the diffusive traveltimes associated with the startup of a gas production well. The inequality constraints were incorporated into the estimates of model parameter resolution and covariance, improving the resolution by roughly 30% to 40%.

The Research of Gas-Water Relations in Low-Permeability Tight Sand Gas Reservoir - Taking Zizhou Gas Field for Example

2013 ◽  
Vol 734-737 ◽  
pp. 480-483
Author(s):  
Jun Bao Ma ◽  
Yu Long Ma ◽  
Chao Sun ◽  
Jian Guo Wang
Keyword(s):  
Water Relations ◽  
Water Distribution ◽  
Low Permeability ◽  
Distribution Law ◽  
Deep Basin ◽  
Gas Reservoir ◽  
Gas Field ◽  
Structural Position ◽  
Single Well ◽  
Tight Sand Gas

The gas-water relations of low-permeability tight sand gas reservoir are complex and not necessarily linked to the structural relief, phenomenon that water is distributed in high structural position while gas in low structural position is common what makes it difficult to make a refined description of gas-water relations and distribution low. The article takes Zizhou gas field for example, establishes 4 gas-water relations modes of single well to analyze some profiles where there is abnormal phenomenon water up gas down, the fact is that water and gas are distributed in different sand bodies and Zizhou Gas Field is not a deep basin gas reservoir. The research shows the phenomenon that water up gas down does not exist, the gas-water relations are normal. The research results have certain significance for the determination of gas-water distribution law.

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