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.

scholarly journals Fracture Characteristics and Their Influence on Gas Seepage in Tight Gas Reservoirs in the Kelasu Thrust Belt (Kuqa Depression, NW China)

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2808
Author(s):  
Yue Dong ◽  
Xuesong Lu ◽  
Junjia Fan ◽  
Qingong Zhuo
Keyword(s):  
Fluid Pressure ◽  
Tight Gas ◽  
Thrust Belt ◽  
Fracture Density ◽  
Fracture Networks ◽  
Gas Reservoirs ◽  
Thin Sections ◽  
Tight Gas Reservoirs ◽  
Gas Seepage ◽  
Aperture Width

Natural fractures were generally accepted as a key factor influencing the gas seepage performance in tight gas reservoirs in Kelasu Thrust Belt (KTB). However, the mechanism was not fully clarified, especially from a microscopic perspective. Based on observation of core samples and cast thin sections and gas charging experiment on core plugs, the parameters of fractures and seepage performance in fractured tight reservoirs are studied; further, the controlling effect of fractures on gas seepage was discussed. The results show that in KTB fractures could be categorized by the size of their apertures as macro-fractures (aperture width ranges from 0.1 to 2 mm) and micro-fractures (aperture width ranges from 5 to 100 μm), which appear in the form of fractures networks. Tectonic deformations and abnormal high fluid pressure control the fracture density: near faults or anticlines (folds), fracture density increases, and fluid pressure of 15 MPa increases the aperture by 50%, and induces new fractures. The fracture networks with high linear density significantly improves tight reservoir quality and seepage performance: it enhances the reservoir permeability by 1–4 orders of magnitude, and the relative gas permeability by 2–10 magnitude; by enhancing permeability, the fracture networks reduce the initial flowing gradient from as high as 0.41 MPa/cm to 0 Mpa/cm, and make the gas flowing possible.

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.

Data Acquistion and Formation Evaluation Strategies in Anistrospic, Tight Gas Reservoirs

2008 ◽  
Author(s):  
Hans de Koningh ◽  
Bernd Heinrich Herold ◽  
Koksal Cig ◽  
Fahd Ali ◽  
Sultan Mahruqy ◽  
...  
Keyword(s):  
Tight Gas ◽  
Gas Reservoirs ◽  
Tight Gas Reservoirs ◽  
Formation Evaluation ◽  
Evaluation Strategies ◽  
Data Acquistion
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