Methane Plumes Research Articles

Aeolian abrasion of rocks as a mechanism to produce methane in the Martian atmosphere

Seasonal changes in methane background levels and methane spikes have been detected in situ a metre above the Martian surface, and larger methane plumes detected via ground-based remote sensing, however their origin have not yet been adequately explained. Proposed methane sources include the UV irradiation of meteoritic-derived organic matter, hydrothermal reactions with olivine, organic breakdown via meteoroid impact, release from gas hydrates, biological production, or the release of methane from fluid inclusions in basalt during aeolian erosion. Here we quantify for the first time the potential importance of aeolian abrasion as a mechanism for releasing trapped methane from within rocks, by coupling estimates of present day surface wind abrasion with the methane contents of a variety of Martian meteorites, analogue terrestrial basalts and analogue terrestrial sedimentary rocks. We demonstrate that the abrasion of basalt under present day Martian rates of aeolian erosion is highly unlikely to produce detectable changes in methane concentrations in the atmosphere. We further show that, although there is a greater potential for methane production from the aeolian abrasion of certain sedimentary rocks, to produce the magnitude of methane concentrations analysed by the Curiosity rover they would have to contain methane in similar concentrations as economic reserved of biogenic/thermogenic deposits on Earth. Therefore we suggest that aeolian abrasion is an unlikely origin of the methane detected in the Martian atmosphere, and that other methane sources are required.

Anomalous Concentration of Methane Emissions at the Continental Shelf Edge of the Northern Cascadia Margin

AbstractA recent compilation of methane plumes detected offshore Washington State includes 1,772 individual bubble streams issuing from 491 discrete vent sites. The majority of these plume sites form a narrow 10‐km‐wide band located shallower than 250‐m water depth, with most sites located near the 175‐m‐deep continental shelf break that tracks the head scarps of large submarine canyons. Archive multichannel seismic profiles over the Cascadia shelf and uppermost margin that were co‐located within a few hundred meters with active emission sites show that methane bubble streams arise from listric/normal faults and triangular‐shaped regions of disturbed seismic reflectors that intersect the seafloor and extend several kilometers into the subsurface. Geological processes were evaluated for producing the narrow emission site depths including nonuniform distribution of methane within the Cascadia accretionary sediment wedge and horizontal transfer of groundwater from onshore subaerial sources. A model of enhanced sediment permeability arising from a contrasting response between the inner and outer portions of the accretionary wedge deformation during a megathrust earthquake cycle appears the most likely mechanism. This faulting is generated during extension of the overriding plate during megathrust earthquake cycles, with semicontinuous permeability enhancement of the fluid pathways from excitation by contemporary incident seismic waves.

An improved method for mobile characterisation of <i>δ</i><sup>13</sup>CH<sub>4</sub> source signatures and its application in Germany

Abstract. The carbon isotopic signature (δ13CH4) of several methane sources in Germany (around Heidelberg and in North Rhine-Westphalia) were characterised. Mobile measurements of the plume of CH4 sources are carried out using an analyser based on cavity ring-down spectroscopy (CRDS). To achieve precise results a CRDS analyser, which measures methane (CH4), carbon dioxide (CO2) and their 13C-to-12C ratios, was characterised especially with regard to cross sensitivities of composition differences of the gas matrix in air samples or calibration tanks. The two most important gases which affect δ13CH4 are water vapour (H2O) and ethane (C2H6). To avoid the cross sensitivity with H2O, the air is dried with a Nafion dryer during mobile measurements. C2H6 is typically abundant in natural gases and thus in methane plumes or samples originating from natural gas. A C2H6 correction and calibration are essential to obtain accurate δ13CH4 results, which can deviate by up to 3 ‰ depending on whether a C2H6 correction is applied. The isotopic signature is determined with the Miller–Tans approach and the York fitting method. During 21 field campaigns the mean δ13CH4 signatures of three dairy farms (-63.9±0.9‰), a biogas plant (-62.4±1.2‰), a landfill (-58.7±3.3‰), a wastewater treatment plant (-52.5±1.4‰), an active deep coal mine (-56.0±2.3‰) and two natural gas storage and gas compressor stations (-46.1±0.8‰) were recorded. In addition, between December 2016 and November 2018 gas samples from the Heidelberg natural gas distribution network were measured with a mean δ13CH4 value of -43.3±0.8‰. Contrary to previous measurements between 1991 and 1996 by Levin et al. (1999), no strong seasonal cycle is shown.

Atmospheric transport of subsurface, sporadic, time-varying methane releases on Mars

This study is devoted to the general circulation modeling (GCM) of methane transport in the Martian atmosphere. A localized source originating from a near-subsurface methane reservoir is considered in the GCM simulations, which are performed with a modified version of the Weather Research and Forecasting (WRF) model, MarsWRF. The localized strength of a methane source varies with time, based on a 1-D near-subsurface diffusive transport. Time-varying surface release scenarios are also compared with an instantaneous release scenario. After release from the surface, the methane transport is investigated in the GCM as a passive scalar over time scales varying between 15 and 60 days, much shorter than the photochemical lifetime. Different emission scenarios of various duration and source intensity, as well as multiple locations with different elevation and terrain complexity are considered, to reproduce the substantial concentrations of methane (up to 50 ppb) observed in the northern hemisphere of Mars in 2003 (Mumma et al., 2009). Among the scenarios considered, the observations are reproduced best for an emission scenario of 45 sols duration, during which a total amount of about 90,000 metric tons of methane is released. The results reveal that observed Mars methane plumes in the northern hemisphere of Mars by Mumma et al. (2009) can be reproduced using a localized, time-varying methane source, consistent with a near surface methane reservoir.

Methane emissions from conventional and unconventional oil and gas production sites in southeastern Saskatchewan, Canada

Energy development in southeastern Saskatchewan, Canada, is unique because conventional and unconventional oil and gas production is co-located. Mobile surveys are ideal for understanding emissions in this area because the overlap of production makes it difficult for airborne or satellite-based methods to differentiate emissions from each type of infrastructure. In this study, we conducted truck-based mobile surveys in the unconventional Canadian Bakken and conventional Weyburn-Midale fields to enumerate and attribute individual methane plumes, estimate methane (CH4) emission rates, and compare emission vectors. We sampled downwind of 645 conventional and 289 unconventional sites, covering over 4500 km of public roads. We found that 28% of surveyed conventional sites were emitting, compared to 32% of surveyed unconventional sites. Mean emissions intensities in each development were 20 m3CH4/day per conventional site and 59 m3CH4/day per unconventional site. Emissions intensities in southeastern Saskatchewan fall on the lower range of other emissions estimates from developments in the US and Canada.

Quantifying methane point sources from fine-scale satellite observations of atmospheric methane plumes

Abstract. Anthropogenic methane emissions originate from a large number of relatively small point sources. The planned GHGSat satellite fleet aims to quantify emissions from individual point sources by measuring methane column plumes over selected ∼10×10 km2 domains with ≤50×50 m2 pixel resolution and 1 %–5 % measurement precision. Here we develop algorithms for retrieving point source rates from such measurements. We simulate a large ensemble of instantaneous methane column plumes at 50×50 m2 pixel resolution for a range of atmospheric conditions using the Weather Research and Forecasting model (WRF) in large eddy simulation (LES) mode and adding instrument noise. We show that standard methods to infer source rates by Gaussian plume inversion or source pixel mass balance are prone to large errors because the turbulence cannot be properly parameterized on the small scale of instantaneous methane plumes. The integrated mass enhancement (IME) method, which relates total plume mass to source rate, and the cross-sectional flux method, which infers source rate from fluxes across plume transects, are better adapted to the problem. We show that the IME method with local measurements of the 10 m wind speed can infer source rates with an error of 0.07–0.17 t h-1+5 %–12 % depending on instrument precision (1 %–5 %). The cross-sectional flux method has slightly larger errors (0.07–0.26 t h-1+8 %–12 %) but a simpler physical basis. For comparison, point sources larger than 0.3 t h−1 contribute more than 75 % of methane emissions reported to the US Greenhouse Gas Reporting Program. Additional error applies if local wind speed measurements are not available and may dominate the overall error at low wind speeds. Low winds are beneficial for source detection but detrimental for source quantification.

Methane seepages in the northern South China Sea: evidence from in situ measurements

Continental margins in world oceans contain large amounts of marine gas hydrates. Changes in the temperature and pressure of sediment may destabilize the methane hydrate, leading to its release and seepage into the sea. This process would increase the dissolved methane in the ambient seawater. In this study, a methane sensor was used to detect methane anomalies in the water column in southwestern Dongsha and Shenhu, northern slope of the South China Sea. Methane plumes were detected at stations SCS001 and T001 in the southwestern Dongsha area, and station SCS002 in the Shenhu area, respectively. The maximum methane concentrations were 8.8 nmol/L in southwestern Dongsha and 10.1 nmol/L in Shenhu, which are about 4-5 times higher than the background methane concentration. This indicates that there are active methane seepages present in both the southwestern Dongsha and Shenhu areas, which are likely related to a methane hydrate reservoir beneath the seafloor. A methane sensor with a low detection limit is a practical instrument with which to detect methane plumes in oceanic environments and to monitor methane leakage from the seafloor.

Evaluating the effects of surface properties on methane retrievals using a synthetic airborne visible/infrared imaging spectrometer next generation (AVIRIS-NG) image

Atmospheric methane has been increasing since the beginning of the industrial era due to anthropogenic emissions. Methane has many sources, both natural and anthropogenic, and there continues to be considerable uncertainty regarding the contribution of each source to the total methane budget. Thus, remote sensing techniques for monitoring and measuring methane emissions are of increasing interest. Recently, the Airborne Visible-Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) has proven to be a valuable instrument for quantitative mapping of methane plumes. Despite this success, uncertainties remain regarding the sensitivity of the retrieval algorithms, including the influence of albedo and the impact of surfaces that may cause spurious signals. To explore these sensitivities, we applied the Iterative Maximum a Posterior Differential Optical Absorption Spectroscopy (IMAP-DOAS) methane retrieval algorithm to synthetic reflected radiances with variable methane concentrations, albedo, surface cover, and aerosols. This allowed for characterizing retrieval performance, including potential sensitivity to variable surfaces, low albedo surfaces, and surfaces known to cause spurious signals. We found that dark surfaces (below 0.10 μWcm−2nm−1sr−1 at 2139 nm), such as water and green vegetation, and materials with absorption features in the 2200–2400 nm range caused higher errors in retrieval results. We also found that aerosols have little influence on retrievals in the SWIR. Results from the synthetic scene are consistent with those observed in IMAP-DOAS retrievals for real AVIRIS-NG scenes containing methane plumes from a waste dairy lagoon and coal mine ventilation shafts. Understanding the effect of surface properties on methane retrievals is important given the increased use of AVIRIS-NG to map gas plumes from a diversity of sources over variable landscapes.

Survival of non-psychrophilic methanogens exposed to martian diurnal and 48-h temperature cycles

Polygonal ground and other geomorphological features reminiscent of recent freeze/thaw cycling are evident on Mars, despite the widespread belief that the planet is currently inhospitably cold and dry. On Earth, permafrost microbial communities are subjected to wide ranges in temperature and are often active at subfreezing temperatures. The existence of active microbial communities within permafrost on Earth suggests that permafrost on Mars may constitute a habitable environment.Terrestrial microbial permafrost communities typically contain methane-producing Archaea, which is cause for concern as global temperatures rise, resulting in permafrost thaw and the release of the potent greenhouse gas. Similarly, on Mars, the overlap between patterned ground and detections of localized methane plumes suggest that the compound may have been released from thawing permafrost.Analyses of permafrost ice cores and soil samples on Earth note that (1) archaeal communities often contain both mesophiles and psychrophiles at different depths and (2) active methane is being produced at subfreezing temperatures over geological timescales. Thus, the purpose of the experiments described here was to determine the effect of extreme temperature changes (reminiscent of the martian diurnal temperature cycle) on the growth and survival of four non-psychrophilic methanogens previously used as models for potential life on Mars. The results indicate that non-psychrophilic methanogens are capable of survival during extreme diurnal and 48-h temperature changes, similar to those on Mars.

Martian methane plume models for defining Mars rover methane source search strategies

AbstractThe detection of atmospheric methane on Mars implies an active methane source. This introduces the possibility of a biotic source with the implied need to determine whether the methane is indeed biotic in nature or geologically generated. There is a clear need for robotic algorithms which are capable of manoeuvring a rover through a methane plume on Mars to locate its source. We explore aspects of Mars methane plume modelling to reveal complex dynamics characterized by advection and diffusion. A statistical analysis of the plume model has been performed and compared to analyses of terrestrial plume models. Finally, we consider a robotic search strategy to find a methane plume source. We find that gradient-based techniques are ineffective, but that more sophisticated model-based search strategies are unlikely to be available in near-term rover missions.

British Columbia lowballs gas well emissions

British Columbia’s natural gas wells emit significantly more methane than the government estimates, suggests a David Suzuki Foundation study released on Jan. 31. Researchers used infrared cameras to identify plumes of methane escaping from vents, then put balloons over the leaks to measure volumes. They found more than 27 m3 per day of methane vented on average for each of the 49 wells surveyed in August 2015 in northeastern British Columbia. That rate translates to an annual total of 83,000 metric tons for the province’s 13,000 active gas wells. In contrast, the provincial government estimates total fugitive methane emissions from all parts of the oil and gas industry at about 78,000 metric tons in 2012, the most recent estimate. “The B.C. Oil & Gas Commission has already been working on initiatives that were recommended in the report, including developing a broader field-sample program to better quantify methane emissions, and fugitive

Cascadia Onshore‐Offshore Site Response, Submarine Sediment Mobilization, and Earthquake Recurrence

AbstractLocal geologic structure and topography may modify arriving seismic waves. This inherent variation in shaking, or “site response,” may affect the distribution of slope failures and redistribution of submarine sediments. I used seafloor seismic data from the 2011 to 2015 Cascadia Initiative and permanent onshore seismic networks to derive estimates of site response, denoted Sn, in low‐ and high‐frequency (0.02–1 and 1–10 Hz) passbands. For three shaking metrics (peak velocity and acceleration and energy density) Sn varies similarly throughout Cascadia and changes primarily in the direction of convergence, roughly east‐west. In the two passbands, Sn patterns offshore are nearly opposite and range over an order of magnitude or more across Cascadia. Sn patterns broadly may be attributed to sediment resonance and attenuation. This and an abrupt step in the east‐west trend of Sn suggest that changes in topography and structure at the edge of the continental margin significantly impact shaking. These patterns also correlate with gravity lows diagnostic of marginal basins and methane plumes channeled within shelf‐bounding faults. Offshore Sn exceeds that onshore in both passbands, and the steepest slopes and shelf coincide with the relatively greatest and smallest Sn estimates at low and high frequencies, respectively; these results should be considered in submarine shaking‐triggered slope stability failure studies. Significant north‐south Sn variations are not apparent, but sparse sampling does not permit rejection of the hypothesis that the southerly decrease in intervals between shaking‐triggered turbidites and great earthquakes inferred by Goldfinger et al. (2012, 2013, 2016) and Priest et al. (2017) is due to inherently stronger shaking southward.

Deep Sea Bottom Methane Hydrate Investigations Aboard Fisheries Training Ship

Since 2013, we have been investigating the presence of methane hydrate in the sea bottom of the Joetsu Basin at depth of 560-580 m via observations mainly taken aboard the fisheries training ship “Nagasaka-maru” which is operated by Nagasaki University. The four cruises were conducted around the middle of May, during the years 2014-2017. The “Nagasaki-maru” and the crew have excellent skills for the usage of the quantitative echo sounder, for fixing the ship's position relative to the sea bottom and for dredging and core sampling. During our cruises, we observed methane plume echoes at precise seafloor locations using the echo sounder and obtained methane hydrate core samples from the seafloor. In 12th of May 2018, following the retirement of the third ship of that name, we conducted our fifth observation cruise aboard the newly commissioned “Nagasaki-maru”, which was launched in October 2017, and have obtained even more detailed information from our targeted methane hydrate areas.

Impact of an historic underground gas well blowout on the current methane chemistry in a shallow groundwater system

Blowouts present a small but genuine risk when drilling into the deep subsurface and can have an immediate and significant impact on the surrounding environment. Nevertheless, studies that document their long-term impact are scarce. In 1965, a catastrophic underground blowout occurred during the drilling of a gas well in The Netherlands, which led to the uncontrolled release of large amounts of natural gas from the reservoir to the surface. In this study, the remaining impact on methane chemistry in the overlying aquifers was investigated. Methane concentrations higher than 10 mg/L (n = 12) were all found to have δ13C-CH4 values larger than -30‰, typical of a thermogenic origin. Both δ13C-CH4 and δD-CH4 correspond to the isotopic composition of the gas reservoir. Based on analysis of local groundwater flow conditions, this methane is not a remnant but most likely the result of ongoing leakage from the reservoir as a result of the blowout. Progressive enrichment of both δ13C-CH4 and δD-CH4 is observed with increasing distance and decreasing methane concentrations. The calculated isotopic fractionation factors of εC = 3 and εD = 54 suggest anaerobic methane oxidation is partly responsible for the observed decrease in concentrations. Elevated dissolved iron and manganese concentrations at the fringe of the methane plume show that oxidation is primarily mediated by the reduction of iron and manganese oxides. Combined, the data reveal the long-term impact that underground gas well blowouts may have on groundwater chemistry, as well as the important role of anaerobic oxidation in controlling the fate of dissolved methane.

Gaussian model for emission rate measurement of heated plumes using hyperspectral data

This paper presents a novel model for measuring the emission rate of a heated gas plume using hyperspectral data from an FTIR imaging spectrometer. The radiative transfer equation (RTE) is used to relate the spectral intensity of a pixel to presumed Gaussian distributions of volume fraction and temperature within the plume, along a line-of-sight that corresponds to the pixel, whereas previous techniques exclusively presume uniform distributions for these parameters. Estimates of volume fraction and temperature are converted to a column density by integrating the local molecular density along each path. Image correlation velocimetry is then employed on raw spectral intensity images to estimate the volume-weighted normal velocity at each pixel. Finally, integrating the product of velocity and column density along a control surface yields an estimate of the instantaneous emission rate. For validation, emission rate estimates were derived from synthetic hyperspectral images of a heated methane plume, generated using data from a large-eddy simulation. Calculating the RTE with Gaussian distributions of volume fraction and temperature, instead of uniform distributions, improved the accuracy of column density measurement by 14%. Moreover, the mean methane emission rate measured using our approach was within 4% of the ground truth. These results support the use of Gaussian distributions of thermodynamic properties in calculation of the RTE for optical gas diagnostics.

Airborne DOAS retrievals of methane, carbon dioxide, and water vapor concentrations at high spatial resolution: application to AVIRIS-NG

Abstract. At local scales, emissions of methane and carbon dioxide are highly uncertain. Localized sources of both trace gases can create strong local gradients in its columnar abundance, which can be discerned using absorption spectroscopy at high spatial resolution. In a previous study, more than 250 methane plumes were observed in the San Juan Basin near Four Corners during April 2015 using the next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) and a linearized matched filter. For the first time, we apply the iterative maximum a posteriori differential optical absorption spectroscopy (IMAP-DOAS) method to AVIRIS-NG data and generate gas concentration maps for methane, carbon dioxide, and water vapor plumes. This demonstrates a comprehensive greenhouse gas monitoring capability that targets methane and carbon dioxide, the two dominant anthropogenic climate-forcing agents. Water vapor results indicate the ability of these retrievals to distinguish between methane and water vapor despite spectral interference in the shortwave infrared. We focus on selected cases from anthropogenic and natural sources, including emissions from mine ventilation shafts, a gas processing plant, tank, pipeline leak, and natural seep. In addition, carbon dioxide emissions were mapped from the flue-gas stacks of two coal-fired power plants and a water vapor plume was observed from the combined sources of cooling towers and cooling ponds. Observed plumes were consistent with known and suspected emission sources verified by the true color AVIRIS-NG scenes and higher-resolution Google Earth imagery. Real-time detection and geolocation of methane plumes by AVIRIS-NG provided unambiguous identification of individual emission source locations and communication to a ground team for rapid follow-up. This permitted verification of a number of methane emission sources using a thermal camera, including a tank and buried natural gas pipeline.

Mobile measurement of methane emissions from natural gas developments in northeastern British Columbia, Canada

Abstract. North American leaders recently committed to reducing methane emissions from the oil and gas sector, but information on current emissions from upstream oil and gas developments in Canada are lacking. This study examined the occurrence of methane plumes in an area of unconventional natural gas development in northwestern Canada. In August to September 2015 we completed almost 8000 km of vehicle-based survey campaigns on public roads dissecting oil and gas infrastructure, such as well pads and processing facilities. We surveyed six routes 3–6 times each, which brought us past over 1600 unique well pads and facilities managed by more than 50 different operators. To attribute on-road plumes to oil- and gas-related sources we used gas signatures of residual excess concentrations (anomalies above background) less than 500 m downwind from potential oil and gas emission sources. All results represent emissions greater than our minimum detection limit of 0.59 g s−1 at our average detection distance (319 m). Unlike many other oil and gas developments in the US for which methane measurements have been reported recently, the methane concentrations we measured were close to normal atmospheric levels, except inside natural gas plumes. Roughly 47 % of active wells emitted methane-rich plumes above our minimum detection limit. Multiple sites that pre-date the recent unconventional natural gas development were found to be emitting, and we observed that the majority of these older wells were associated with emissions on all survey repeats. We also observed emissions from gas processing facilities that were highly repeatable. Emission patterns in this area were best explained by infrastructure age and type. Extrapolating our results across all oil and gas infrastructure in the Montney area, we estimate that the emission sources we located (emitting at a rate > 0.59 g s−1) contribute more than 111 800 t of methane annually to the atmosphere. This value exceeds reported bottom-up estimates of 78 000 t of methane for all oil and gas sector sources in British Columbia. Current bottom-up methods for estimating methane emissions do not normally calculate the fraction of emitting oil and gas infrastructure with thorough on-ground measurements. However, this study demonstrates that mobile surveys could provide a more accurate representation of the number of emission sources in an oil and gas development. This study presents the first mobile collection of methane emissions from oil and gas infrastructure in British Columbia, and these results can be used to inform policy development in an era of methane emission reduction efforts.

Differential Absorption Lidar (DIAL) Measurements of Landfill Methane Emissions

Methane is one of the most important gaseous hydrocarbon species for both industrial and environmental reasons. Understanding and quantifying methane emissions to atmosphere is therefore an important element of climate change research. Range-resolved infrared differential absorption Lidar (DIAL) measurements provide the means to map and quantify a wide range of different methane sources. This paper describes the DIAL measurement technique and reports the application of an infrared DIAL system to field measurements of methane emissions from active and closed landfill sites. This paper shows how the capability of the DIAL to measure the spatial distribution of methane plumes enables DIAL vertical scans to spatially separate and independently quantify emissions from different sources. It also allows DIAL horizontal scans carried out above the surface to identify emission hot-spots. An overview of the landfill emission surveys carried out over the last decade by the National Physical Laboratory (NPL) DIAL system is presented. These surveys were part of research projects and commercial works aimed to validate the method and to provide reliable information on the methane emissions measuring the total site and area-specific emissions from active areas, capped areas, and gas engine stacks. This work showed that methane emissions are significantly higher for active sites than closed sites due to the methane emitted directly to air from the uncapped active areas. On active sites, the operational tipping areas generally have higher emission levels than the capped areas, although there is considerably variation in the emission from different capped areas. The information obtained with DIAL measurements allow site operators to identify significant fugitive emission sources and validate emissions estimates, and they allow the regulators to revise and update the emission inventories. Operators’ remediation actions driven by DIAL measurements have also been shown to considerably decreased total site methane emission.

The vertical transport of methane from different potential emission types on Mars

AbstractThe contrasting evolutionary behavior of the vertical profile of methane from three potential release scenarios is analyzed using a global circulation model with assimilated temperature profiles. Understanding the evolving methane distribution is essential for interpretation of future retrievals of the methane vertical profile taken by instruments on the ExoMars Trace Gas Orbiter spacecraft. We show that at methane release rates constrained by previous observations and modeling studies, discriminating whether the methane source is a sustained or instantaneous surface emission requires at least 10 sols of tracking the emission. A methane source must also be observed within 5 to 10 sols of the initial emission to distinguish whether the emission occurs directly at the surface or within the atmosphere via destabilization of metastable clathrates. Assimilation of thermal data is shown to be critical for the most accurate backtracking of an observed methane plume to its origin.

日本海東縁,直江津沖に巨大メタンプリュームと海底メタンハイドレートの発見(8.海洋地質)

日本海東縁,直江津沖に巨大メタンプリュームと海底メタンハイドレートの発見(8.海洋地質)