Repository for Oil and Gas Energy Research (ROGER)

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The state of Oklahoma has experienced a dramatic increase in the amount of measurable seismic activities over the last decade. The needs of a petroleum-driven world have led to increased production utilizing various technologies to reach energy reserves locked in tight formations and stimulate end-of-life wells, creating significant amounts of undesirable wastewater ultimately injected underground for disposal. Using Phased Array L-band Synthetic Aperture Radar (PALSAR) data, we performed a differential Synthetic Aperture Radar Interferometry (InSAR) technique referred to as the Small BAseline Subset (SBAS)-based analysis over east central Oklahoma to identify ground surface deformation with respect to the location of wastewater injection wells for the period of December 2006 to January 2011. Our results show broad spatial correlation between SBAS-derived deformation and the locations of injection wells. We also observed significant uplift over Cushing, Oklahoma, the largest above ground crude oil storage facility in the world, and a key hub of the Keystone Pipeline. This finding has significant implications for the oil and gas industry due to its close proximity to the zones of increased seismicity attributed to wastewater injection. Results southeast of Drumright, Oklahoma represent an excellent example of the potential of InSAR, identifying a fault bordered by an area of subduction to the west and uplift to the east. This differentiated movement along the fault may help explain the lack of any seismic activity in this area, despite the large number of wells and high volume of fluid injected.

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The dramatic rise in Oklahoma seismicity since 2009 is due to wastewater injection. The role of injection depth is an open, complex issue, yet critical for hazard assessment and regulation. We developed an advanced Bayesian Network to model joint conditional dependencies between spatial, operational, and seismicity parameters. We found injection depth relative to crystalline basement most strongly correlates with seismic moment release. The joint effects of depth and volume are critical, as injection rate becomes more influential near the basement interface. Restricting injection depths to 200–500 m above basement could reduce annual seismic moment release by a factor of 1.4–2.8. Our approach enables identification of sub-regions where targeted regulation may mitigate effects of induced earthquakes, aiding operators and regulators in wastewater disposal regions.

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Understanding the causes of human-induced earthquakes is paramount to reducing societal risk. We investigated five cases of seismicity associated with hydraulic fracturing (HF) in Ohio since 2013 that, because of their isolation from other injection activities, provide an ideal setting for studying the relations between high-pressure injection and earthquakes. Our analysis revealed two distinct groups: (i) deeper earthquakes in the Precambrian basement, with larger magnitudes (M > 2), b-values < 1, and many post–shut-in earthquakes, versus (ii) shallower earthquakes in Paleozoic rocks ∼400 m below HF, with smaller magnitudes (M < 1), b-values > 1.5, and few post–shut-in earthquakes. Based on geologic history, laboratory experiments, and fault modeling, we interpret the deep seismicity as slip on more mature faults in older crystalline rocks and the shallow seismicity as slip on immature faults in younger sedimentary rocks. This suggests that HF inducing deeper seismicity may pose higher seismic hazards. Wells inducing deeper seismicity produced more water than wells with shallow seismicity, indicating more extensive hydrologic connections outside the target formation, consistent with pore pressure diffusion influencing seismicity. However, for both groups, the 2 to 3 h between onset of HF and seismicity is too short for typical fluid pressure diffusion rates across distances of ∼1 km and argues for poroelastic stress transfer also having a primary influence on seismicity.

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Seismicity curbed by lowering volume Determining why hydraulic fracturing (also known as fracking) triggered earthquakes in the Duvernay Formation in Canada is important for future hazard mitigation. Schultz et al. found that injection volume was the key operational parameter correlated with induced earthquakes in the Duvernay. However, geological factors also played a considerable role in determining whether a large injection volume would trigger earthquakes. These findings provide a framework that may lead to better forecasting of induced seismicity. Science, this issue p. 304 A sharp increase in the frequency of earthquakes near Fox Creek, Alberta, began in December 2013 in response to hydraulic fracturing. Using a hydraulic fracturing database, we explore relationships between injection parameters and seismicity response. We show that induced earthquakes are associated with completions that used larger injection volumes (104 to 105 cubic meters) and that seismic productivity scales linearly with injection volume. Injection pressure and rate have an insignificant association with seismic response. Further findings suggest that geological factors play a prominent role in seismic productivity, as evidenced by spatial correlations. Together, volume and geological factors account for ~96% of the variability in the induced earthquake rate near Fox Creek. This result is quantified by a seismogenic index–modified frequency-magnitude distribution, providing a framework to forecast induced seismicity. Induced seismicity from hydrofracturing in Canada is related to the well fluid injection volumes. Induced seismicity from hydrofracturing in Canada is related to the well fluid injection volumes.

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The annual earthquake rate in Oklahoma (United States) has increased dramatically in recent years, owing in large part to the rapid proliferation of salt-water disposal (SWD) wells associated with unconventional oil and gas recovery. This study presents a geospatial analysis of earthquake occurrence and SWD volume within a 68,420 km2 area in north-central Oklahoma between 2011 and 2016. Results indicate that (1) the annual geographic centroid of Arbuckle Group SWD well locations predicts the geographic centroid for M3.0+ earthquake occurrence within an ~1σ radius of gyration when the well centroid is geometrically weighted by SWD volume; (2) between 2014 and 2016 Arbuckle SWD volume and earthquake occurrence are spatially cross-correlated to a length scale of 125 km; and (3) earthquake mitigation strategies implemented in late 2015 and 2016 are preferentially affecting the joint variability of SWD volume and small-magnitude earthquakes. These results suggest that current earthquake mitigation may require further volume reductions and/or greater areal extent to increase effectiveness.

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A rapid increase of injection-induced earthquakes (IIE) is often linked to a higher level of seismic hazard. In this study, we compare the geodetically-defined moment rate to seismicity distribution in western Canada where significant IIE are observed. The regional seismic pattern is dominated by IIE, both in number and moment, along a 150-km wide NW–SE band of moderate strain rate in the easternmost Cordillera and foothills. The observed rate of moment release from local earthquakes is much closer to the tectonic moment rate in the IIE-dominated areas. We conclude that, on a regional scale, tectonic strain rate is an important control on IIE. Injection in areas with moderate tectonic strain may temporarily increase the local seismic hazard, but widespread IIE over an extended period of time may deplete the available tectonic moment and could, under the right conditions, have a limited long-term effect of reducing regional seismic hazard.

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Shale gas could help address the insatiable global demand for energy. However, in addition to risks of environmental pollution, the risk of induced seismicity during the hydraulic fracturing process is often considered as the major showstopper in the public acceptability of shale gas as an alternative source of fossil fuel. Other types of subsurface energy development have also demonstrated similar induced seismicity risks. This article presents an interdisciplinary review of notable cases of suspected induced seismicity relating to subsurface energy operations, covering operations for hydraulic fracturing, wastewater injection, conventional gas extraction, enhanced geothermal systems and water impoundment. Possible causal mechanisms of induced seismicity are described and illustrated, then methods to mitigate induced seismicity, encompassing regulations, including so-called traffic light systems, monitoring and assessment, and numerical modeling approaches for predicting the occurrence of induced seismicity are outlined. Issues relating to public perception of energy technologies in regards to induced seismicity potential are also discussed. This article is categorized under: Photovoltaics > Climate and Environment Fossil Fuels > Climate and Environment Energy Infrastructure > Economics and Policy Energy and Development > Systems and Infrastructure

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Focal mechanisms of induced earthquakes reflect anthropogenic contributions to pre-existing geological features and fault slippages. In this paper, we examine fault-related (double-couple, DC) and possibly fluid-related (non-double-couple, non-DC) mechanisms of induced earthquakes (M2-6) at regional scales. We systematically compare well-resolved focal mechanisms of 33 events in the Western Canada Sedimentary Basin, among which 12 were induced by hydraulic fracturing and one by secondary recovery. Most of the seismicity is dominated by strike-slip/thrust faulting regimes, whereas limited (but consistent) non-DC components are obtained from injection-induced seismicity in central Alberta. We interpret the persistent compensated-linear-victor-dipole (CLVD) components (M2.1-3.8) as reflecting fracture growth and/or non-coplanar faults slippages during hydraulic fracturing stimulations. We further expand the moment tensor decomposition analysis to four representative classes of induced seismicity globally and find that the overall contribution of non-DC components is largely comparable between induced and tectonic earthquakes.

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In this paper, a fuzzy comprehensive evaluation (FCE) based on the analytic hierarchy process (AHP) model (FAHP) has been established to quantitatively evaluate the seismic risk of the region with covers 3080.25 km2 including hydraulic fracturing operation areas. Taking into account the combined effect exerted by influencing factors such as geological structures, the seismic history and the stress accumulation, etc., five major factors are identified, namely, seismicity rates (Z value), magnitude-frequency coefficients (b value), reservoirs, regional geotectonic (distribution of active faults), stress fields and the spatial distribution of fracturing platforms. In addition to using massive raw data as objective information, this model takes experts' assessments as the subjective judgment of expertise. According to the maximum membership principle, the most favorable risk evaluation have been made in 625 grids with optimized results through methods of the weighted average and the interpolation. Comprehensive evaluation maps have been drawn based on the seismic data from 2008 to 2016 used in modeling and have been validated by the seismic data in 2017. Results show that most of the seismic events in 2017 have fit into the high-risk area, especially those felt earthquakes larger than magnitude 3 have entirely fit into the medium-high risk area after the interpolation, indicating that the assessment results have certain objectivity and accuracy.

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The cumulative seismic moment is a robust measure of the earthquake response to fluid injection for injection volumes ranging from 3100 to about 12 million m3. Over this range, the moment release is limited to twice the product of the shear modulus and the volume of injected fluid. This relation also applies at the much smaller injection volumes of the field experiment in France reported by Guglielmi, et al. (2015) and laboratory experiments to simulate hydraulic fracturing described by Goodfellow, et al. (2015). In both of these studies, the relevant moment release for comparison with the fluid injection was aseismic and consistent with the scaling that applies to the much larger volumes associated with injection-induced earthquakes with magnitudes extending up to 5.8. Neither the micro-earthquakes, at the site in France, nor the acoustic emission in the laboratory samples contributed significantly to the deformation due to fluid injection.

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Presently, consensus on the incorporation of induced earthquakes into seismic hazard has yet to be established. For example, the nonstationary, spatiotemporal nature of induced earthquakes is not well understood. Specific to the Western Canada Sedimentary Basin, geological bias in seismogenic activation potential has been suggested to control the spatial distribution of induced earthquakes regionally. In this paper, we train a machine learning algorithm to systemically evaluate tectonic, geomechanical, and hydrological proxies suspected to control induced seismicity. Feature importance suggests that proximity to basement, in situ stress, proximity to fossil reef margins, lithium concentration, and rate of natural seismicity are among the strongest model predictors. Our derived seismogenic potential map faithfully reproduces the current distribution of induced seismicity and is suggestive of other regions which may be prone to induced earthquakes. The refinement of induced seismicity geological susceptibility may become an important technique to identify significant underlying geological features and address induced seismic hazard forecasting issues.

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Knowledge of the geometric properties of fractures and cracks in a petroleum reservoir is important to reservoir exploitation. When aligned and partially connected, fractures and cracks can act as conduits for fluid flow and thus can significantly increase the permeability of the reservoir. The aligned fractures and cracks, on the other hand, are an effective means to generate seismic anisotropy. In this study, we utilize the seismic data recorded by a vertical array installed in a shallow borehole at a shale play site in southwest China. By applying seismic interferometry to the ambient noise data recorded by 12 three-component geophones, we extract P and S waves propagating vertically along the borehole. The S waves show up to 20% velocity variations with respect to their polarization directions. Such large S-wave anisotropy can be explained by the horizontal transverse isotropic (HTI) model and is likely caused by natural fractures that are widely present in the area and align approximately in the NE-SW direction. During the 13-day period of hydraulic fracking treatment, we also observe large and systematic temporal variations in S-wave velocity, degree of S-wave polarization anisotropy, and fast polarization direction. By comparing our observations with normal strain changes calculated with a half-space elastic model, we speculate that strain changes induced by hydraulic injection and fracturing are likely to be responsible for the observed temporal variations in seismic anisotropy. As such, seismic interferometry with shallow borehole acquisition might provide an alternative means to monitor hydraulic fracturing and wastewater injection in the future.

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This paper examines the impact of earthquakes on residential property values using sales data from Oklahoma from 2006 to 2014. Before 2010, Oklahoma had only a couple of earthquakes per year that were strong enough to be felt by residents. Since 2010, seismic activity has increased, bringing potentially damaging quakes several times each year and perceptible quakes every few days. Using repeat-sales and difference-in-differences models, we estimate that prices decline by 3–4 percent after a home has experienced a moderate earthquake measuring 4 or 5 on the Modified Mercalli Intensity Scale. Prices can decline 9 percent or more after a potentially damaging earthquake with intensity above 6. We also find significant increases in the time-on-market after earthquake exposures. Our findings are consistent with the experience of an earthquake revealing a new disamenity and risk that is then capitalized into house values.

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New aeromagnetic survey data collected over north-central Oklahoma image possible seismogenic faults in the crystalline basement. Linear earthquake sequences associated with induced seismicity suggest the re-activation of ancient basement faults, but few of these sequences are aligned with mapped faults. The new data show many earthquake sequences aligned with linear magnetic gradients or offsets between anomalies, while mapped faults, which mainly describe sedimentary cover, show limited correspondence with either. This strongly suggests significant structural differences between the crystalline basement and sedimentary cover. Furthermore, while the earthquakes are occurring on re-activated ancient faults, most of these faults have likely been inactive for millions of years. The magnetic data exhibit many gradient lineaments that are optimally oriented for fault slip, and the earthquake data suggest additional optimally oriented faults. Together these data suggest the presence of potentially numerous seismogenic faults throughout the region, which may contribute to high levels of induced seismicity.

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The ability of fluid-generated subsurface stress changes to trigger earthquakes has long been recognized. However, the dramatic rise in the rate of human-induced earthquakes in the past decade has created abundant opportunities to study induced earthquakes and triggering processes. This review briefly summarizes early studies but focuses on results from induced earthquakes during the past 10 years related to fluid injection in petroleum fields. Study of these earthquakes has resulted in insights into physical processes and has identified knowledge gaps and future research directions. Induced earthquakes are challenging to identify using seismological methods, and faults and reefs strongly modulate spatial and temporal patterns of induced seismicity. However, the similarity of induced and natural seismicity provides an effective tool for studying earthquake processes. With continuing development of energy resources, increased interest in carbon sequestration, and construction of large dams, induced seismicity will continue to pose a hazard in coming years. Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 46 is May 30, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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We analyze the background seismicity, initiation, and earliest stages of the Guy‐Greenbrier, Arkansas, earthquake sequence, which was potentially induced by wastewater injection starting in July 2010,...A magnitude 4.7 earthquake occurred in Arkansas in 2011, after several months of smaller earthquakes that started in July 2010. Many scientists think that pumping wastewater (from oil and gas production)...

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To assess whether recent seismicity is induced by human activity or is of natural origin, we analyze fault displacements on high-resolution seismic reflection profiles for two regions in the central United States (CUS): the Fort Worth Basin (FWB) of Texas and the northern Mississippi embayment (NME). Since 2009, earthquake activity in the CUS has increased markedly, and numerous publications suggest that this increase is primarily due to induced earthquakes caused by deep-well injection of wastewater, both flowback water from hydrofracturing operations and produced water accompanying hydrocarbon production. Alternatively, some argue that these earthquakes are natural and that the seismicity increase is a normal variation that occurs over millions of years. Our analysis shows that within the NME, faults deform both Quaternary alluvium and underlying sediments dating from Paleozoic through Tertiary, with displacement increasing with geologic unit age, documenting a long history of natural activity. In the FWB, a region of ongoing wastewater injection, basement faults show deformation of the Proterozoic and Paleozoic units, but little or no deformation of younger strata. Specifically, vertical displacements in the post-Pennsylvanian formations, if any, are below the resolution (~15 m) of the seismic data, far less than expected had these faults accumulated deformation over millions of years. Our results support the assertion that recent FWB earthquakes are of induced origin; this conclusion is entirely independent of analyses correlating seismicity and wastewater injection practices. To our knowledge, this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques. Long-term fault slip history can diagnose natural versus induced earthquakes, independent of correlations with fluid injection. Long-term fault slip history can diagnose natural versus induced earthquakes, independent of correlations with fluid injection.

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Hydraulic fracturing is a key technology to stimulate oil and gas wells to increase production in shale reservoirs with low permeability. Generally, the stimulated reservoir volume is performed based on pre-existing natural fractures (NF). Hydraulic fracturing in shale reservoirs with large natural fractures (i.e., faults) often results in fault activation and seismicity. In this paper, a coupled hydro-mechanical model was employed to investigate the effects of injection site on fault activation and seismicity. A moment tensor method was used to evaluate the magnitude and affected areas of seismic events. The micro-parameters of the proposed model were calibrated through analytical solutions of the interaction between hydraulic fractures (HF) and the fault. The results indicated that the slip displacement and activation range of the fault first decreased, then remained stable with the increase in the distance between the injection hole and the fault (Lif). In the scenario of the shortest Lif (Lif = 10 m), the b-value—which represents the proportion of frequency of small events in comparison with large events—reached its maximum value, and the magnitude of concentrated seismic events were in the range of −3.5 to −1.5. The frequency of seismic events containing only one crack was the lowest, and that of seismic events containing more than ten cracks was the highest. The interaction between the injection-induced stress disturbance and fault slip was gentle when Lif was longer than the critical distance (Lif = 40–50 m). The results may help optimize the fracturing treatment designs during hydraulic fracturing.

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Each of the three earthquake sequences in Oklahoma in 2016—Fairview, Pawnee, and Cushing—appears to have been induced by high-volume wastewater disposal within 10 km. The Fairview M5.1 main shock was part of a 2 year sequence of more than 150 events of M3, or greater; the main shock accounted for about half of the total moment. The foreshocks and aftershocks of the M5.8 Pawnee earthquake were too small and too few to contribute significantly to the cumulative moment; instead, nearly all of the moment induced by wastewater injection was focused on the main shock. The M5.0 Cushing event is part of a sequence that includes 48 earthquakes of M3, or greater, that are mostly foreshocks. The cumulative moment for each of the three sequences during 2016, as well as that for the 2011 Prague, Oklahoma, and nine other sequences representing a broad range of injected volume, are all limited by the total volumes of wastewater injected locally.

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We produce a one‐year 2017 seismic‐hazard forecast for the central and eastern United States from induced and natural earthquakes that updates the 2016 one‐year forecast; this map is intended to provide information to the public and to facilitate the development of induced seismicity forecasting models, methods, and data. The 2017 hazard model applies the same methodology and input logic tree as the 2016 forecast, but with an updated earthquake catalog. We also evaluate the 2016 seismic‐hazard forecast to improve future assessments. The 2016 forecast indicated high seismic hazard (greater than 1% probability of potentially damaging ground shaking in one year) in five focus areas: Oklahoma–Kansas, the Raton basin (Colorado/New Mexico border), north Texas, north Arkansas, and the New Madrid Seismic Zone. During 2016, several damaging induced earthquakes occurred in Oklahoma within the highest hazard region of the 2016 forecast; all of the 21 moment magnitude (M) ≥4 and 3 M≥5 earthquakes occurred within the highest hazard area in the 2016 forecast. Outside the Oklahoma–Kansas focus area, two earthquakes with M≥4 occurred near Trinidad, Colorado (in the Raton basin focus area), but no earthquakes with M≥2.7 were observed in the north Texas or north Arkansas focus areas. Several observations of damaging ground‐shaking levels were also recorded in the highest hazard region of Oklahoma. The 2017 forecasted seismic rates are lower in regions of induced activity due to lower rates of earthquakes in 2016 compared with 2015, which may be related to decreased wastewater injection caused by regulatory actions or by a decrease in unconventional oil and gas production. Nevertheless, the 2017 forecasted hazard is still significantly elevated in Oklahoma compared to the hazard calculated from seismicity before 2009.

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In this article we review the stress-strain relationships that take place in the crust during some of the main hydrocarbon production and storage processes: gas extraction; water injection in wells to stimulate the extraction of oil (EOR); unconventional hydrocarbon production by hydraulic fracturing (fracking); disposal of wastewater (saline water) from the extraction of conventional and unconventional hydrocarbons such as saline water return (flowback) of hydraulic fracturing, both with TDS higher than 40 000 mg/ L. In addition, the type of faults that are more likely to slip and the induced seismicity related to the production and extraction of hydrocarbons are analysed.

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In this article, we analyzed the recent seismic activity in the northern Montney Play of British Columbia in 2015 and its connection with fluid injection (hydraulic fracturing and long‐term injection of gas and wastewater disposal) in the region. The earthquake sequence used in this study includes 676 events from 3 October 2014 to 31 December 2015 from the Progress Energy earthquake catalog with moment magnitude as small as 1. Spatial and temporal correlation of seismic activity with the fluid injection in the region revealed that these events are better correlated with hydraulic fracturing (correlation coefficient of ∼0.17 at confidence level close to 99.7%, with a lag time between 0 and 2 days) than other types of injection. Using the double‐difference relocation technique, we obtained depth constraints for some of the events for which supplementary, industry‐provided waveforms were available. The depths of these events range from 0.5 to 2.5 km and are mostly constrained above the target zone where hydraulic fracturing was taking place. The best‐fit moment tensor solution for the event on 17 August 2015 gives a moment magnitude of 4.6 and a predominantly thrust mechanism in the northwest–southeast direction with a shallow focal depth of 4 km. This is consistent with that obtained through double‐difference relocation for this event (1.3 km), given the depth uncertainty of the moment tensor inversion. Electronic Supplement:Tables of injection volumes and seismicity parameters, and figure of monthly distribution of seismic events and location of fluid injection sites in the vicinity of the 17 August 2015 Mw 4.6 event.

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Media attention to earthquake risks linked to the underground injection of produced waters from oil and gas fracking operations has increased over the past few years. However, little scholarly attention has been devoted to newspaper coverage of events and state policy actions that are associated with “induced seismicity.” A key concern addressed in this article is whether newspaper coverage is largely unrestrained or is restricted by other factors. Is coverage by differing newspapers influenced by frames emphasizing the economic importance of oil and gas production within the state? We conclude that the answer is “yes” based on information gleaned from content analyses of newspapers in Ohio, Oklahoma, and Texas from 2009 through 2014. Related Articles

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This paper summarizes the current state of understanding regarding the induced seismicity in connection with hydraulic fracturing operations targeting the Duvernay Formation in central Alberta, near the town of Fox Creek. We demonstrate that earthquakes in this region cluster into distinct sequences in time, space, and focal mechanism using (i) cross-correlation detection methods to delineate transient temporal relationships, (ii) double-difference relocations to confirm spatial clustering, and (iii) moment tensor solutions to assess fault motion consistency. The spatiotemporal clustering of the earthquake sequences is strongly related to the nearby hydraulic fracturing operations. In addition, we identify a preference for strike-slip motions on subvertical faults with an approximate 45° P axis orientation, consistent with expectation from the ambient stress field. The hypocentral geometries for two of the largest-magnitude (M ~4) sequences that are robustly constrained by local array data provide compelling evidence for planar features starting at Duvernay Formation depths and extending into the shallow Precambrian basement. We interpret these lineaments as subvertical faults orientated approximately north-south, consistent with the regional moment tensor solutions. Finally, we conclude that the sequences were triggered by pore pressure increases in response to hydraulic fracturing stimulations along previously existing faults.

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It is now well established that past and current geo-energy resource recovery operations associated with geothermal systems, oil and natural gas recovery operations, and long-term underground storage of waste fluids can induce earthquakes, some having magnitudes as great as 5–6. Injection into or removal of fluids from existing faults and highly stressed rocks associated with energy resource recovery and waste fluid disposal can generate the stress changes needed for fault rupture and slip along the fault plane. Important aspects of the present state of knowledge of induced seismicity, including causal mechanisms, characteristics of different energy technologies, hydraulic fracturing and waste disposal injection wells, carbon capture and storage, and assessing and managing the hazards and risks from induced seismicity are summarized in this paper. Induced earthquakes occur at shallower depths than natural tectonic earthquakes, and for a given magnitude event, shaking intensity is more severe in the epicentral region of an induced earthquake but dissipates more rapidly with distance than for a natural earthquake. In general, the greater the imbalance between the extraction and injection volumes at a site, the larger the magnitude of an observed induced earthquake. The likelihood of shaking of a given intensity at a given location can change with time for anthropogenic events in response to variations in source locations and fluid injection and withdrawal rates and volumes. Methods to account for these variations in seismic hazard and risk assessment are under development.

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The development of shale gas reservoirs through the use of hydraulic fracturing continues to raise debates on the possible environmental effects. Most dominant of this debate is the likely effect of seismic events upon stimulating the reservoirs through hydraulic fracturing. Hydraulic fracturing remains the most effective technique for production optimisation from tight reservoirs. Although in the UK it has been in use since 1957 in one form or another plans to develop unconventional resource using this technique in the future has been met with stiff opposition especially since hydraulic fracturing operation at Preese Hall 1 conducted by Cuadrilla in 2010 resulted in induced seismic events of magnitude 1.5 and 2.3 on Richter's scale. The link to hydraulic fracturing and the associated seismic effects, however, are unclear especially in the UK and even in cases where such seismic events are recorded, of what magnitude are they, and their likely effect on people, buildings etc. By reviewing data on over 2000 onshore wells in the United Kingdom, 7.4% of the total wells were found to have had some technique performed on them that assumed fracturing of the reservoir rock, such as hydraulic fracturing and disposal water injection. This was in reasonable agreement to the figure of 10% reported by the royal society. Reviewing the seismic database of British Geological Society (BGS) at 5 km radius around locations of identified wells the potential magnitude of seismic events at and around these wells were analysed. Results show that there was no obvious correlation between the location of the seismic events and the location of the wells known to have been hydraulically fractured. Apart from Preese Hall 1 case post-treatment seismic activity levels ware identical to pre-treatment levels. Only Preese Hall 1 had a seismic activity spike around the date of treatment and location of the well. Also since the seismic recording timeframe was from 1970, majority of the wells identified to have had some form of hydraulic fracturing couldn't be reviewed for possible seismicity as the treatments happened before this recording time frame. Recorded seismic events around these wells were found to be too low to have caused any major effect, the highest occurrence between the ranges of 0.3 ML–1.5 ML.

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We compare current and historic seismicity rates in six States in the USA and three Provinces in Canada to past and present hydrocarbon production. All States/Provinces are major hydrocarbon producers. Our analyses span three to five decades depending on data availability. Total hydrocarbon production has significantly increased in the past few years in these regions. Increased production in most areas is due to large-scale hydraulic fracturing and thus underground fluid injection. Furthermore, increased hydrocarbon production generally leads to increased water production, which must be treated, recycled or disposed of underground. Increased fluid injection enhances the likelihood of fault reactivation, which may affect current seismicity rates. We find that increased seismicity in Oklahoma, likely due to salt-water disposal, has an 85% correlation with oil production. Yet, the other areas do not display State/Province-wide correlations between increased seismicity and production, despite 8-16 fold increases in production in some States. However in various cases seismicity has locally increased. Multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates, including (i) the near-surface tectonic background rate, (ii) the existence of critically stressed and favorably oriented faults, which must be hydraulically connected to injection wells, (iii) the orientation and magnitudes of the in situ stress field, combined with (iv) the injection volumes and implemented depletion strategies. A comparison with the seismic hazard maps for the USA and Canada shows that induced seismicity is less likely in areas with a lower hazard. The opposite however is not necessarily true.

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Over the last decade, unconventional oil and gas production has increased due to use of hydraulic fracturing and second oil recovery techniques. However, this activity is followed by prevalence of induced seismicity and has the potential to damage pipelines. The integrity of these pipelines is essential for oil and gas companies, regulator organizations, and stakeholders due to adverse environmental consequences and significant financial losses. Therefore, it is important to investigate a potential impact of the induced seismicity on the pipeline infrastructure in order to enhance informed decision making (e.g. permitting decisions). To accomplish this task, this paper presents a probabilistic seismic risk assessment approach, which has been used for pipeline infrastructure located in the Northeast of British Columbia, Canada. Spatial clustering analysis is used for earthquakes, previously registered in the region, to delineate areas, which are particularly prone to the induced seismicity. The state-of-the-art ground motion prediction equation for induced seismicity is applied in Monte Carlo simulation to obtain a stochastic field of the seismic intensity. Based on the pipelines’ seismic fragility formulations as well as its mechanical characteristics and corrosion conditions, spatial and probabilistic distributions of the repair rate and probability of failure have been obtained and visualized with the aid of the Geospatial Information System.

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Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where seismic hazard is now approaching the tectonic levels of parts of California. Unclear in the highly charged debate over expansion of shale gas recovery has been the role of hydraulic fracturing (fracking) in causing increased levels of induced seismicity. Opponents to shale gas development have vilified fracking as directly responsible for this increase in seismicity. However, this purported causal link is not substantiated; the predominant view is that triggering in the midwestern United States is principally a result of massive reinjection of energy-coproduced wastewaters. On page 1406 of this issue, Bao and Eaton (5) identify at least one example of seismicity developed from hydraulic fracturing for shale gas in the Alberta Basin. Observational data sets provide a clearer picture of the causes of induced seismicity Observational data sets provide a clearer picture of the causes of induced seismicity

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Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO2 geological storage.

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We model pore-pressure diffusion caused by pressurized waste-fluid injection at two nearby wells and then compare the buildup of pressure with the observed initiation and migration of earthquakes during the early part of the 2010–2011 Guy–Greenbrier earthquake swarm. Pore-pressure diffusion is calculated using MODFLOW 2005 that allows the actual injection histories (volume/day) at the two wells to diffuse through a fractured and faulted 3D aquifer system representing the eastern Arkoma basin. The aquifer system is calibrated using the observed water-level recovery following well shut-in at three wells. We estimate that the hydraulic conductivities of the Boone Formation and Arbuckle Group are 2.2 × 10−2 and 2.03 × 10−3 m day−1, respectively, with a hydraulic conductivity of 1.92 × 10−2 m day−1 in the Hunton Group when considering 1.72 × 10−3 m day−1 in the Chattanooga Shale. Based on the simulated pressure field, injection near the relatively conductive Enders and Guy–Greenbrier faults (that hydraulically connect the Arbuckle Group with the underlying basement) permits pressure diffusion into the crystalline basement, but the effective radius of influence is limited in depth by the vertical anisotropy of the hydraulic diffusivity. Comparing spatial/temporal changes in the simulated pore-pressure field to the observed seismicity suggests that minimum pore-pressure changes of approximately 0.009 and 0.035 MPa are sufficient to initiate seismic activity within the basement and sedimentary sections of the Guy–Greenbrier fault, respectively. Further, the migration of a second front of seismicity appears to follow the approximately 0.012 MPa and 0.055 MPa pore-pressure fronts within the basement and sedimentary sections, respectively.

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North Texas has experienced a roughly exponential increase in seismicity since 2008. This increase is primarily attributable to wastewater injection into the Ellenburger Formation—a carbonate formation located within and just above seismically active zones. To our knowledge, there has been no previous comprehensive ∼10 year analysis comparing regional seismicity with basin-wide injection and injection pressure of wastewater into the Ellenburger, even though monthly injection/pressure records have been made publically available for nearly a decade. Here we compile and evaluate more than 24,000 monthly injection volume and pressure measurements for the Ellenburger formation. We compare Ellenburger injection pressures and volumes to basin-wide injection pressures and volumes, and to earthquake locations and rates. The analysis shows where cumulative injection volumes are highest, where injection pressures and formation pressures are increasing, how injection volumes have changed regionally with time, and how Ellenburger injection volumes and pressures correlate in space and time with recent seismicity in North Texas. Results indicate that between 2005 and 2014 at least 270 million m3 (∼1.7 billion barrels) of wastewater were injected into the Ellenburger formation. If we assume relative homogeneity for the Ellenburger and no significant fluid loss across the 63,000 km2 basin, this volume of fluid would increase pore fluid pressure within the entire formation by 0.09 MPa (∼13 psi). Recent spot measurements of pressure in the Ellenburger confirm that elevated fluid pressures ranging from 1.7 to 4.5 MPa (250–650 psi) above hydrostatic exist in this formation, and this may promote failure on pre-existing faults in the Ellenburger and underlying basement. The analysis demonstrates a clear spatial and temporal correlation between seismic activity and wastewater injection volumes across the basin, with earthquakes generally occurring in the central and eastern half of the basin, where Ellenburger wastewater injection cumulative volumes and estimated pressure increases are highest. The increased seismicity correlates with increased fluid pressure, which is a potential cause for these earthquakes. Based on these results, we hypothesize it is plausible that the cumulative pressure increase across the basin may trigger earthquakes on faults located tens of kilometers or more from injection wells, and this process may have triggered the Irving-Dallas earthquake sequence. We use these results to develop preliminary forecasts for the region concerning where seismicity will likely continue or develop in the future, and assess what additional data are needed to better forecast and constrain seismic hazard.

Abstract:
Hydraulic fracturing has been inferred to trigger the majority of injection-induced earthquakes in western Canada, in contrast to the midwestern United States where massive saltwater disposal is the dominant triggering mechanism. A template-based earthquake catalog from a seismically active Canadian shale play, combined with comprehensive injection data during a 4-month interval, shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites. The largest event [moment magnitude (MW) 3.9] occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement. Patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of >1 km, whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months.

Abstract:
In order to mitigate CO2 emissions while continuing to use fossil fuels as an energy source, CO2 emissions from large point sources such as power stations can be captured and stored in suitable subsurface sedimentary formations. However, concerns have been raised that the injection of pressurized CO2 may alter the subsurface stress state, leading to the re-activation of faults and generating induced seismic activity. Southeast Saskatchewan has seen extensive oil and gas activity since the 1950s. This activity includes, in recent years, a boom in shale oil production entailing hydraulic fracturing. It is also home to two world-leading CCS projects, the Weyburn-Midale CO2 Monitoring and Storage Project, and the Boundary Dam/Aquistore Project. The aim of this paper is to assess whether any of the conventional oilfield operations, shale oil activity or CCS has caused induced seismicity in southeast Saskatchewan. We find that the region has a very low rate of natural seismicity, and that there is no evidence to suggest that any kind of oilfield activity has caused induced events. However, seismicity has been associated with potash mining activities in the region. It is not clear whether the potash mining-induced events are triggered by subsidence above the mined zones, or by re-injection of waste brines. It is of interest to compare the situation in southeast Saskatchewan with other areas that have seen substantial increases in the amount of injection-induced seismic activity. It is notable that in many areas that have seen injection-induced seismicity, fluid injection is into basal aquifers that are hydraulically connected to the crystalline Precambrian basement. In contrast, most oilfield activities in southeast Saskatchewan are in Carboniferous formations, while the only units to have experienced a net volume increase are of Cretaceous age. It is tentatively suggested that the lack of induced seismic activity is due to the fact that injection is hydraulically isolated from the basement rocks, although it is also possible that stress conditions in the region are less conducive to induced seismicity.

Abstract:
For induced microseismicity associated with hydraulic fracturing, the frequency-magnitude distribution is typically characterized by a falloff with increasing magnitude that is significantly faster than for seismicity along active fault systems. This characteristic may arise from a break in scale invariance, possibly due to mechanical layering that typifies fine-grained sedimentary rocks in many shale gas and tight oil reservoirs. The latter would imply the presence of spatiotemporal magnitude correlations. Using three microseismic catalogs for well stimulations in widely separated locations with varying hydraulic-fracturing methods, we show that events with similar magnitudes indeed tend to cluster in space and time. In addition, we show that the interevent time distribution can be described by a universal functional form characterized by two power laws. One exponent can be related to the presence of interevent triggering as in aftershock sequences and is a consequence of the Omori-Utsu law. The other one is a reflection of the intrinsic spatial variation in the microseismic response rates. Taken together, these features are indicative of nontrivial spatiotemporal clustering of induced microseismicity and, hence, of direct relevance for time-dependent seismic hazard assessment.

Abstract:

Abstract:
The largest recorded earthquake in Kansas occurred northeast of Milan on 12 November 2014 (Mw 4.9) in a region previously devoid of significant seismic activity. Applying multistation processing to data from local stations, we are able to detail the rupture process and rupture geometry of the mainshock, identify the causative fault plane, and delineate the expansion and extent of the subsequent seismic activity. The earthquake followed rapid increases of fluid injection by multiple wastewater injection wells in the vicinity of the fault. The source parameters and behavior of the Milan earthquake and foreshock–aftershock sequence are similar to characteristics of other earthquakes induced by wastewater injection into permeable formations overlying crystalline basement. This earthquake also provides an opportunity to test the empirical relation that uses felt area to estimate moment magnitude for historical earthquakes for Kansas.

Abstract:
We extend spontaneous rupture models in earthquake source studies to analyze fluid injection problems. We perform these analyses on a 2-D fracture network model with a propagating hydraulic fracture (HF) and three sets of natural fractures (NFs). We find that it is difficult for NFs that are either parallel or perpendicular to the HF to slip because of little resolved shear stress on them in the prestress field. Shear failure of optimally oriented NFs depends on frictional parameters, such as the critical slip distance in slip-weakening laws. Slip of NFs near the tips of the HF may affect HF opening. Nonsmooth fracture opening generates isolated spiky seismic signals, while unstable frictional slip radiates strong and continuous seismic signals with long-duration coda waves. These results suggest microseismicity may be primarily generated by unstable frictional slip on NFs with some contribution from nonsmooth opening motions on HFs and/or NFs.

Abstract:
In Texas, earthquakes have occurred in close association with activities accompanying petroleum production since 1925. Here we develop a five‐question test to categorize individual events as “tectonic,” “possibly induced,” “probably induced,” or “almost certainly induced.” In Texas, the probably induced and almost certainly induced earthquakes are broadly distributed geographically—in the Fort Worth basin of north Texas, the Haynesville Shale play area of east Texas, along the Gulf Coast in south Texas, and the Permian basin of west Texas. As the technologies applied to manage petroleum fields have evolved, induced earthquakes have been associated with different practices. In fields being driven by primary recovery prior to 1940, earthquakes occurred in fields extracting high volumes of petroleum from shallow strata. Subsequently, as field pressures decreased and secondary recovery technologies became common, earthquakes also occurred in association with waterflooding operations. Since 2008, the rate of earthquakes with magnitudes greater than 3 has increased from about 2 events/yr to 12 events/yr; much of this change is attributable to earthquakes occurring within a few kilometers of wastewater disposal wells injecting at high monthly rates. For three sequences monitored by temporary local seismograph networks, most hypocenters had focal depths at and deeper than the depth of injection and occurred along mapped faults situated within 2 km of injection sites. The record clearly demonstrates that induced earthquakes have been broadly distributed in several different geographic parts of Texas over the last 90 years.

Abstract:
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.

Abstract:
Fracking of the Preese Hall-1 well in 2011 induced microseismicity that was strong enough to be felt. This occurrence of ‘nuisance’ microearthquakes, unexpected at the time, was a major factor resulting in adverse public opinion against shale gas in the UK and was thus of significant political importance. Despite this, and notwithstanding the technical importance of this instance of induced seismicity for informing future shale gas projects, it has received little integrated study; contradictory results have indeed been reported in analyses that lack integration. This instance therefore provides a case study to illustrate how a small but significant multi-disciplinary geoscience dataset may be put to best use, including how best to quantify uncertainties in key parameters, which may themselves be relatively poorly quantified but whose values may significantly affect the ability to understand the occurrence of induced seismicity. The best-recorded event in this induced microearthquake sequence (at 08:12 on 2 August 2011) is thus assigned an epicentre circa British National Grid reference SD 377358, south of the Preese Hall-1 wellhead, a focal depth of ∼2.5 km, and a focal mechanism with strike 030°, dip 75°, and rake −20°, this NNE-striking nodal plane being the inferred fault plane. Like other parts of Britain, this locality exhibits high differential stress, with maximum and minimum principal stresses roughly north-south and east-west. This instance indeed fits an emerging trend of the occurrence of relatively large induced earthquakes in localities with high differential stress; such an association was predicted many years ago on the basis of experimental rock mechanics data, so observational confirmation might well have been anticipated and should thus not have been unexpected. Many steep faults, striking NNE-SSW or NE-SW, mostly Carboniferous-age normal faults, are present; the stress field is favourably oriented for their left-lateral reactivation, southward leakage of fracking fluid into one such fault having presumably caused the induced seismicity. Given the pervasive presence of similarly oriented faults, future occurrences of similar induced seismicity should be planned for; they pose a significant technical challenge to any future UK shale-gas industry.

Abstract:
An important factor in mitigation of seismic hazard from induced seismicity is properly established seismic networks suitable for consistent identification of small‐to‐moderate events (magnitudes less than four). Here, we evaluate the performance of the newly established regional broadband seismic network in northeast British Columbia, Canada. The seismic network was designed for monitoring of induced seismicity due to oil and gas operations related to hydraulic fracturing and fluid injection in the region. We use regional and local earthquake catalogs for the period 1985–2015 to analyze magnitude of completeness and epicentral uncertainty. We also perform a theoretical assessment of minimum detectable magnitude across the study region based on analysis of ambient noise and simulated ground motions. From the frequency–magnitude distribution of the reported events in the regional earthquake catalog, the magnitude of completeness has decreased ∼1 magnitude unit from ∼3 in the periods 1985–2013 to ∼2 in the period 2013–2015 as a result of the establishment of new stations. The minimum detectable magnitude in the region is 1.6–2.6 based on the signal‐to‐noise ratio (SNR) of 10 and higher at four or more stations. By comparing the regional and dense array catalogs, we determine that the error in epicentral location in well‐constrained areas by seismic stations is below 3 km in both east–west and north–south directions. However, location uncertainties can be up to 10 km in the east–west direction in areas where the current regional network is sparse. The magnitude detection threshold in the Montney Play, where most of the current oil and gas activities are taking place, can be further reduced by up to 1 magnitude unit with the addition of four new stations.

Abstract:
We utilize Transportable Array data to survey regional seismicity in east Texas and northwest Louisiana. Through analyst review and a waveform‐matching technique, we identify 58 earthquakes occurring between April 2010 and July 2012. The earthquakes spatially cluster within two main zones, near Timpson, Texas, and within Bienville Parish, Louisiana; minor clusters occur in the Texas–Louisiana border region. Although the Timpson earthquakes have been studied previously, we identify many undetected earthquakes that occurred in 2010, about two years prior to the 17 May 2012 Mw 4.8 earthquake, which has been linked to wastewater injection. The Bienville Parish sequence, which consists of magnitude 0.5–1.9 earthquakes in mid‐ to late‐2011, occurred about 10 km from wells that began injecting at relatively modest rates (∼40,000 barrels (bbl) per month) in late 2010 but within a few kilometers of production wells that were being hydraulically fractured around the same time period. An additional cluster of seismicity was observed, near Center, Texas, with some seismicity occurring in the months prior to the start of wastewater injection and the largest earthquake in that sequence occurring when injection exceeded 200,000 bbl/month; this may be a case in which injection into a seismically active area promoted a larger earthquake. Finally, there was also seismicity observed near the Toledo Bend Reservoir in Louisiana. The evidence concerning some of the sequences indicates they might be associated with either hydraulic fracturing or recent increases in wastewater injection at wells within the unconventional Haynesville shale gas play. The results of this study highlight the need for more extensive seismic monitoring in the central and eastern regions of the United States of America.

Abstract:
The data we analyzed are from a Marcellus Shale gas field in Greene County, southwestern Pennsylvania. We first investigated the relationship between microseismic event trends and discontinuities extracted from 3D seismic data and their relationship to . This analysis was followed by an examination of the relationship of cumulative gas production to radiated energy, stimulated reservoir volume (SRV), and energy density (ED). We have determined that microseismic event trends observed in multiwell hydraulic fracture treatments were similar to the trends of interpreted small faults and fracture zones extracted from 3D seismic coverage of the area. Hydraulic fracture treatments conducted in six laterals produced clusters of microseismic events with an average trend of N51°E and, to a more limited extent, N56°W. The N51°E microseismic event trend coincided closely with the average N52°E trend of interpreted minor faults and fracture zones extracted from the 3D seismic data. That relationship suggested that microseismic events form through reactivation of old faults and fracture zones in response to an easterly trending . We also found that variations in gas production correlated with variations in radiated microseismic energy ( of 0.985), SRV ( of 0.974), and ED ( of 0.989). SRV is a measure of the volume of space occupied by induced microseismicity, whereas energy release per unit volume (ED) can be directly related to rupture area created through hydraulic fracture stimulation. We suggest that ED serves as a better estimator of production potential in unconventional shale reservoirs.

Abstract:
Knowledge of induced fractures can help to evaluate the success of reservoir stimulation. Seismic P-waves through fracturing media can exhibit azimuthal variation in traveltime, amplitude, and thin-bed tuning, so amplitude variation with azimuth (AVAz) can be used to evaluate the hydraulic-fracturing-caused anisotropy. The Barnett Shale of the Fort Worth Basin was the first large-scale commercial shale gas play. We have analyzed two adjacent Barnett Shale seismic surveys: one acquired before hydraulic fracturing and the other acquired after hydraulic fracturing by more than 400 wells. Although not a rigorous time-lapse experiment, comparison of AVAz anisotropy of these two surveys provided valuable insight into the possible effects of hydraulic fracturing. We found that in the survey acquired prior to hydraulic fracturing, AVAz anomalies were stronger and highly correlated with major structural lineaments measured by curvature. In contrast, AVAz anomalies in the survey acquired after hydraulic fracturing were weaker and compartmentalized by rather than correlated to the most-positive curvature lineaments. We found in five microseismic experiments within the survey that these ridge lineaments form fracture barriers. These findings suggested that future time-lapse experiments may be valuable in mapping the modified horizontal stress field to guide future drilling and in recognizing zones of bypassed pay.