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.

Long-period long-duration seismic events during hydraulic stimulation of shale and tight-gas reservoirs — Part 2: Location and mechanisms

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. KS109-KS117 ◽  
Author(s):  
Indrajit Das ◽  
Mark D. Zoback
Keyword(s):  
Fluid Pressure ◽  
Seismic Events ◽  
Tight Gas ◽  
Gas Reservoirs ◽  
Data Set ◽  
Hydraulic Stimulation ◽  
Tight Gas Reservoirs ◽  
Long Period ◽  
Long Duration ◽  
Stimulation Of

Long-period long-duration (LPLD) seismic events that have been observed during hydraulic stimulation of shale-gas and tight-gas reservoirs appear to represent slow shear slip on relatively large faults. Within the limitations of the recording geometry, we determine the areas in the reservoirs where the events are located in two case studies in the Barnett shale. In one data set, LPLD events appear to occur in the region where the density of natural fractures as well as the fluid pressure during pumping were highest. In the other data set, the LPLD events are observed to occur between two wells and seem to establish a hydraulic connection between them. In both data sets, the LPLD events occur in areas with very few located microearthquakes. A combination of factors such as high fluid pressure and/or high clay content is potentially responsible for the slowly slipping faults. The LPLD events appear to be occurring only on faults large enough to produce a sequence of slow slip events. We suggest that these slowly slipping faults contribute appreciably to the stimulation of these extremely low-permeability reservoirs and hence mapping the distribution of faults and fractures and areas with rock properties that favor slow, sustained slip, can help in optimizing production.

Long-period, long-duration seismic events during hydraulic stimulation of shale and tight-gas reservoirs — Part 1: Waveform characteristics

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. KS97-KS108 ◽  
Author(s):  
Indrajit Das ◽  
Mark D. Zoback
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Events ◽  
Tight Gas ◽  
Gas Reservoirs ◽  
Hydraulic Stimulation ◽  
Tight Gas Reservoirs ◽  
Long Period ◽  
Long Duration ◽  
Low Amplitude ◽  
Stimulation Of

Long-period long-duration (LPLD) seismic events are relatively low-amplitude signals that have been observed during hydraulic fracturing in several shale-gas and tight-gas reservoirs. These events are similar in appearance to tectonic tremor sequences observed in subduction zones and transform fault boundaries. LPLD events are predominantly composed of S-waves, but weaker P-waves have also been identified. In some cases, microearthquakes are observed during the events. Based on the similarity with tectonic tremors and our observations of several impulsive S-wave arrivals within the LPLD events, we interpret the LPLD events as resulting from the superposition of slow shear-slip events on relatively large faults. Most large LPLD waveforms appear to start as a relatively slower, low-amplitude precursor, lacking clear impulsive arrivals. We estimate the energy carried by the larger LPLD events to be [Formula: see text] times greater than a [Formula: see text] microseismic event that is typical of the events that occur during hydraulic stimulation. Over the course of the entire stimulation activity of five wells in the Barnett formation (each hydraulically fractured ten times), the LPLD events were found to cumulatively release over an order of magnitude higher energy than microearthquakes. The large size of these LPLD events, compared to microearthquakes, suggests that they represent slip on relatively large faults during stimulation of these extremely low-permeability reservoirs. Moreover, they imply that the accompanying slow slip on faults, probably mostly undetected, is a significant deformation process during multistage hydraulic fracturing.

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.

Long-period, long-duration seismicity observed during hydraulic fracturing of the Marcellus Shale in Greene County, Pennsylvania

2017 ◽  
Vol 36 (7) ◽  
pp. 580-587 ◽  
Author(s):  
Abhash Kumar ◽  
Erich Zorn ◽  
Richard Hammack ◽  
William Harbert
Keyword(s):  
Hydraulic Fracturing ◽  
Marcellus Shale ◽  
Long Period ◽  
Long Duration ◽  
Greene County
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