CH4 Leakage Research Articles

CH4 hydrate dissociation and CH4 leakage characteristics: Insights from laboratory investigation based on stratified environment reconstruction of natural gas hydrate reservoir

Submarine natural gas hydrates (NGHs) are one of the largest methane reservoirs on Earth, offering huge potential as an alternative energy source and serving as a crucial global carbon sink. However, the substantial risk of methane leakage during NGH development seriously threatens marine and global ecological and environmental safety, presenting a major challenge for commercial NGH exploitation. Focusing on the unknown leakage mechanisms, this study employed a new simulation device to construct a stratified environment and to investigate the characteristics of hydrate dissociation and methane leakage during depressurization production, under conditions of varied fracturing in overlying sediment. A movable module was used to dynamically isolate and connect the hydrate reservoir with the overlying layer. The results showed that the intrusion of overlying water decelerated the reservoir depressurization rate, leading to a mass of hydrate reformation. The invasion locations and flow paths of the overlying water were influenced by the fracture scale of the overlying sediment. Benefiting from the additional sensible heat and reservoir space occupation of the overlying water in the later production stages, the methane recovery ratio in the fracture-containing systems were not significantly affected. However, the leakage methane increased as fracture channels enlarged, reaching up to 9.90 % of the total methane content in the hydrate reservoir. The leakage mechanism primarily involved local overpressure, buoyancy effects, and diffusion. The research, for the first time, experimentally revealed the response relationship between methane leakage and hydrate dissociation, providing foundational data and theoretical support for the safe and efficient NGH development.

Experimental Study on Enhanced Methane Detection Using an MEMS-Pyroelectric Sensor Integrated with a Wavelet Algorithm.

An optical sensing approach that balances portability with cost efficiency has been designed for the reliable monitoring of fugitive methane (CH4) emissions. Employing a LiTaO3-based pyroelectric detector integrated with micro-electro-mechanical systems and a broad infrared source, the developed gas sensor adeptly measured CH4 concentrations with a low limit of detection of about 5.6 ppmv and showed rapid response times with t90 consistently under 3 s. Notably, the novelty of our method lies in its precise control and reduction of CH4 levels, enhanced by wavelet denoising. This technique, optimized through meticulous grid search, effectively mitigated noise interference noticeable at CH4 levels below 10 ppmv. Postdenoising, nonlinear regression analyses based on the modified Beer-Lambert equation returned R2 values of 0.985 and 0.982 for the training and validation sets, respectively. In conclusion, this gas sensor has been shown to be able to meet the requirements for early warning of CH4 leakage on the surface in various carbon capture, utilization, and storage projects such as enhanced oil or gas recovery projects using CO2 injection.

Application of Portable CH4 Detector Based on TDLAS Technology in Natural Gas Purification Plant

Methane (CH4) is the main pollutant in oil and gas production. The detection and accounting of CH4 is an important issue in the process of greenhouse gas control and emission reduction in oil and gas industry. In this study, a portable CH4 detector based on tunable diode laser absorption spectroscopy (TDLAS) technology was deployed. The three-dimensional distribution of CH4 in a natural gas purification plant in Sichuan was obtained through vertical unmanned aerial vehicle (UAV) flight observations and ground mobile observations. According to the mass balance method, the emission of CH4 on 30 m above ground level (AGL) and 60 m AGL in this site was about 0.012 kg/s (±42% at 1σ) and 0.034 kg/s (±47% at 1σ), respectively, in one day. The vertical distribution showed that the CH4 concentration reached the maximum (2.75 ± 0.19 ppm) with height of 0 to 100 m AGL. The CH4 concentration from 100 to 300 m AGL showed a downward trend with height. Atmospheric instability at high altitude and high wind speed promoted the diffusion of CH4. The CH4 concentrations of horizontal distribution on 30 m AGL and 60 m AGL were 2.48 ± 0.11 ppm and 2.76 ± 0.34 ppm. In the observation of mobile campaigns, the connecting equipment of natural gas treatment facilities was prone to leakage, such as in valves and flanges. CH4 leakage was also detected at the torch mouth, especially when there was an open flame at the torch mouth. During the mobile movement investigation, the downwind measurement (OTM-33A) was applied to determine the overall CH4 emission rate shortly after patrolling the site. This work plays a vital role in optimizing the operation and maintenance of natural gas production stations pipe network, ensuring human safety and minimizing greenhouse gas emissions.

Seafloor activity and deep-subsurface geology of gas hydrate areas revealed from δ13C of methane-derived authigenic carbonates along the eastern margin of the Sea of Japan

The collection of microbial CH4 hydrates and methane-derived authigenic carbonates (MDACs) around Sado Island in the Sea of Japan has recently increased. In this study, the carbon isotopic composition of CaCO3 in MDAC (δ13CCaCO3) within these microbial CH4 hydrate areas was compared to that observed at the thermogenic CH4 hydrate mounds of the Umitaka Spur offshore of Joetsu, Sea of Japan. δ13CCaCO3 from thermogenic CH4 hydrate mounds (‐39.1 to -6.1‰ Vienna Pee Dee Belemnite [VPDB]) was more enriched in 13C than those of microbial CH4 areas (‐57.6 to -41.0‰ VPDB). The δ13CCaCO3 variations represented by 2σ standard deviations were also greater for the thermogenic CH4 hydrate mounds (8–11‰) compared to those of the microbial CH4 areas (6–7‰). Because the precipitation of MDACs with various δ13CCaCO3 compositions can occur over areas undergoing dynamic geochemical changes, larger variations suggest that the current thermogenic CH4 hydrate mounds with active gas seepage must have been geochemically dynamic during past MDAC precipitation. Oil-containing gas hydrates in the thermogenic CH4 hydrate mounds suggest a link with deep oil and gas reservoirs. CH4 leakage from deep-subsurface gas reservoirs may drive the higher activity observed at shallow sediment depths in thermogenic CH4 hydrate mounds. δ13CCaCO3 variations revealed differences in paleogeochemical dynamics at shallow sediment depths, and the geochemical characteristics may provide insights into deep-subsurface geological situations for CH4 supply.

Tracking Carbon Flows in China's Iron and Steel Industry.

Accurately tracking carbon flows is the first step toward reducing the climate impacts of the iron and steel industry (ISI), which is still lacking in China. In this study, we track carbon flows from coal/mineral mines to end steel users by coupling the cross-process material and energy flow model, point-based emission inventory, and interprovincial trade matrices. In 2020, ISI emitted 2288 Tg of CO2 equivalent (CO2eq, including CH4 and CO2), 96% of which came from energy use and 4% from raw material decomposition. Often overlooked off-gas use and CH4 leakage in coal mines account for 25% of life-cycle emissions. Due to limited scrap resources and a high proportion of pig iron feed, the life-cycle emission intensity of the electric arc furnace (EAF) (1.15 t CO2eq/t steel) is slightly lower than the basic oxygen furnace (BOF) (1.58 t CO2eq/t steel) in China. In addition, over 49% of producer-based emissions are driven by interprovincial coal/coke/steel trade. In particular, nearly all user-based emissions in Zhejiang and Beijing are transferred to steelmaking bases. Therefore, we highlight the need for life-cycle and spatial shifts in user-side carbon management.

On the correlation between thermal imagery and fugitive CH4 emissions from MSW landfills

Landfill gas (LFG) is related to the biochemical processes generating heat and releasing CH4, CO2, and other gases in lower concentrations, which result in environmental impacts and risk of local explosion. Thermal infrared imagery (TIR) is employed to detect CH4 leakage as a risk control approach. However, the challenge for LFG leakage detection using TIR is establishing a relation between the gas flux and the ground temperature. This study evaluates the problem of a heated gas flowing through a porous medium column where the upward surface exchanges heat by radiation and convection to the environment. A heat transfer model that considers the upward LFG flow is proposed, and a sensibility analysis is developed to relate the flux to the ground temperature level in the condition of non-income solar radiation. An explicit equation to predict CH4 fugitive flow as a function of temperature anomalies of the ground was presented for the first time. The results show that the predicted ground surface temperatures are consistent with the literature’s experimental observations. Moreover, the model was complementarily applied to a Brazilian landfill, with in situ TIR measurements in an area with a slightly fractured cover. In this field observation, the predicted CH4 flux was around 9025 g m−2 d−1. Model limitations concerning the soil homogeneity, the transient variation of atmospheric conditions or local pressure, and soil temperature difference in low-flux conditions (related to TIR-cameras accuracy) require further validation. Results could help landfill monitoring in conditions of a high-temperature ground anomaly in dry seasons.

Thermally-induced diffusion on methane mass transfer in high-pressure aqueous solutions

This paper has investigated the mass transfer process of methane (CH4) in aqueous solution under the effect of temperature gradient using quantitative Raman spectroscopy. At 20 MPa and 473.15 K, it was observed that CH4 diffuses from low concentration position to high driven by temperature gradient, indicating that thermodynamic factors play a dominant role. According to the assumption that the saturated concentration of CH4 is treated as steady concentration profile, Soret and thermal diffusion coefficients of dissolved CH4 in the range of 1 ∼ 200 MPa and 273.15 ∼ 600 K are calculated. Based on the temperature gradient distribution calculated by thermal model in the Ashizuri section of the Nankai Trough, this paper estimates the CH4 solubility distribution in this section and provides a new perspective to reveal a possible formation mechanism of CH4 accumulation, leakage and related geological disasters in the geological body.

Research progress on low-concentration methane oxidation using palladium-based catalysts

There is low concentration (0.05% to 0.5%) of CH4 leakage in marine natural gas engine exhaust. It is difficult to capture and utilize low concentration CH4 because of its stable chemical structure and high ignition temperature. Catalytic oxidation is the main method to remove low concentration CH4 from tail gas. The noble metal palladium (Pd) is the best catalytic material for the complete oxidation of low concentration CH4. In this paper, the main research progress of Pd-based catalysts is reviewed for their low-temperature activity, reliability and development cost. Initially, the impact of Pd particle dimensions and valence distribution, Pd dispersion, carrier identity and strong metal-carrier interaction (SMSI) on the catalyst's methane oxidation activity was elucidated. Then, the mechanism of methane oxidation on the surface of Pdbased catalysts is summarized; In addition, the deactivation mechanisms of Pd-based catalysts, such as high temperature sintering, water poisoning and sulphur poisoning, are described in detail. In conclusion, the major hurdles encountered in achieving full oxidation of methane at low concentrations are outlined, along with the future development direction for methane oxidation catalysts. Additionally, strategies to enhance the performance of Pd-based catalysts are briefly suggested. The modified Text maintains a clear, professional, and concise style with minimal changes.

Methane Leakage Measurement of Natural Gas Heating Boilers and Greenhouse Gas Emissions Accounting of “Coal-to-Gas” Transition for Residential Heating in Rural Beijing

The “coal-to-gas” transition, a widely advancing replacement of coal with natural gas (NG) for residential heating in northern China since 2017, has been confirmed to have significant environmental and health benefits. Since China proposed carbon peaking and carbon neutrality targets, the importance of accurately measuring the emissions of greenhouse gases (GHGs), mainly carbon dioxide (CO2) and methane (CH4), has been highlighted. However, due to the deficient estimates of CH4 leakage from natural gas heating boilers (namely, “gas boilers”), there is still a lack of reliable assessment of its GHG emissions. Here, applying a high-precision CO2–CH4 analyzer, we examined 30 gas boilers in Beijing, China. Based on stoichiometry, emission factor, and global warming potential (GWP) methods, we estimated the CH4 leakage rates of gas boilers and reassessed the reduction in GHG emissions from the transition. Considering the CH4 leakage rate of gas boilers, which was 0.22% [0.13, 0.30]%, the “coal-to-gas” transition for residential heating in rural Beijing reduced GHG emissions by 44.8% in end use. Our findings fill the gaps in CH4 leakage measurement and GHG emissions accounting and provide data support for the amendment of NG appliance standards and the evaluation of energy transition policies in China.

Formula omitted] gas leakage detection method for low contrast infrared images

The leakage of CH4 gas not only pollutes the environment, but also poses a serious threat to social safety and human health. Infrared imaging is an effective method for detecting CH4 gas leakage. It has the advantages of convenient operation and noncontact. However, compared with general infrared images, gas infrared images have lower contrast and more blurred edges. When the CH4 leakage is small, the detection methods are easily disturbed by noise. To solve this problem, this paper proposes a detection method for CH4 gas leakage based on a Gaussian mixture model and a Kernel density estimation model. First, in the preprocessing part, the improved adaptive anisotropic diffusion filter is used to denoise and preserve the edge of the image. Then, we employ the fast and robust fuzzy c-means clustering (FRFCM) guided contrast limited adaptive histogram equalization (CLAHE) method to enhance the details of the infrared image to improve the local contrast. Finally, the Gaussian mixture model and improved Kernel density estimation model are cascaded to segment the gas area and mark leakage areas. The experiment results demonstrate that our proposed method has more significant segmentation and anti-jamming ability than other algorithms under indoor conditions of 30 mL/min and 0.8 m. It can effectively detect the CH4 leakage area and has a higher accuracy rate and lower false positive rate.

Numerical Evaluation of a Novel Development Mode for Challenging Oceanic Gas Hydrates Considering Methane Leakage

The exploitation of challenging oceanic gas hydrate reservoirs with low permeability and permeable boundary layers faces the challenges of methane leakage and low production. Considering this aspect, a novel five-spot injection–production system combined with hydraulic fracturing was proposed. In particular, the potential of this development mode, including hydrate dissociation, gas production, and gas capture, was evaluated in comparison with a three-spot injection–production system. The results showed that increasing the fracture conductivity cannot prevent CH4 leakage in the three-spot, and the leakage accounted for 5.6% of the total gas production, even at the maximum fracture conductivity of 40 D·cm. Additionally, the leakage amount increased as the well spacing increased, and the leakage accounted for 36.7% of the total gas production when the well spacing was 140 m. However, the proposed development mode completely addressed CH4 leakage and significantly increased gas production. The average gas production rate reached 142 m3/d per unit length of the horizontal section, which was expected to reach the commercial threshold. The variance analysis indicated that optimal plans for the challenging hydrates in the Shenhu area were well spacing of 100–120 m and fracture conductivity greater than 20 D·cm.

Quantitatively evaluating greenhouse gas leakage from CO2 enhanced oil recovery fields

Greenhouse gas (mainly CO2 and CH4) leakage from abandoned wells in CO2 enhanced oil recovery sites is a long-standing environmental concern and health hazard. Although multiple CO2 capture, utilization, and storage programs, e.g., CarbonSAFE and Regional Carbon Storage Partnerships, have been developed in the U.S. to reach the net-zero emission target by 2050, one cannot neglect the significant amount of CO2 and CH4 leakage from abandoned wells. This study will investigate the potential of CO2 and oil components leakages from the abandoned wellbore and develop the first-ever quantitative approach to evaluating CO2 and oil component leakage from a CO2 enhanced oil recovery field. Results show that in addition to a large amount of CO2 leakage, a significant amount of light and intermediate oil components leaked through the wellbore. In contrast, a minimal amount of heavy oil component leaked. Oil components’ leakage is mainly through the gas phase rather than the liquid phase. CO2 leakage is positively correlated to reservoir depth, wellbore pressure, and permeability through sensitivity analysis. In contrast, it is negatively related to net-to-gross ratio, residual oil saturation, and mole fraction of CH4. On the other hand, oil component leakages are positively correlated to all uncertain parameters, except the net-to-gross ratio. Lastly, the reduced-order models generated using the machine learning technique have a relatively high fidelity. Cited as: Chen, B., Mehana, M. Z., Pawar, R. J. Quantitatively evaluating greenhouse gas leakage from CO2 enhanced oil recovery fields. Advances in Geo-Energy Research, 2023, 7(1): 20-27. https://doi.org/10.46690/ager.2023.01.03

Coupled Simulation of Hydrate-Bearing and Overburden Sedimentary Layers to Study Hydrate Dissociation and Methane Leakage

Methane leakage during natural gas hydrate (NGH) exploitation is one of the important challenges restricting its safe development, which necessitates further investigation. However, only a few experimental studies have been conducted to characterize the relationship between methane (CH4) leakage and NGH exploitation. The CH4 leakage mechanism and controlling factors in the hydrate dissociation process are still unclear. A coupled simulator has been developed to study the CH4 hydrate exploitation and the possible leakage of CH4. The new system overcomes the difficulty of constructing hydrate-free overlying strata and seawater in previous studies and can simulate the in situ natural environment containing hydrate reservoirs, overlying strata and overlying seawater as well. In addition, the simulator integrates the spatial distribution of temperature, pressure and electric resistance in hydrate reservoir systems, and allows for the visual monitoring of the overlying strata and the sampling of overburden gas and liquids. The effectiveness of the coupled simulations was verified through experimental testing. The coupled simulations allowed for the characterization of the CH4 leakage mechanism and can be used to develop safe strategies for NGH exploitation.

Effects of key geological factors in the long-term transport of CH4 and the CH4-hydrate formation behavior with formation dip

Methane hydrates (MH) are widely distributed below seafloor at marine locations. Most MH bearing geological deposits have dip angles because of the complicated geological structure and diagenesis. In this study, the impact of formation dip on CH4 migration and the associated MH formation was systematically investigated numerically. A numerical model was set up based on the geological information in the Shenhu area of Baiyun Sag in the northern South China Sea (SCS) to simulate the long-term transport of CH4 and the associated MH formation with formation dip. We further conducted a sensitivity analysis and a statistical analysis on three key geological parameters (i.e., dip angle, CH4 leakage rate, and water salinity). The results indicate that the dip angle (θ) of the reservoir promotes the lateral migration of CH4. The total accumulated amount of MH decreases 2.45% with θ increasing from 0° to 10°. Sensitivity analysis suggested that the formation of MH predominantly depends on the CH4 leakage rate (RCH4) in inclined reservoirs. The lateral migration distance of CH4 increases 13.1% but the total accumulated amount of MH decreases 8.8% with increasing water salinity (Xi) from 3.0 wt% to 3.5 wt%. We further analyzed the effect of heterogeneity, which shows that the inclined reservoir with alternating sand and clay layers favors MH formation more than a uniform reservoir with an 8.8% increase in the total MH. Understanding the effect of formation dip on the transport of CH4 and MH formation provide a useful reference in the identification of marine MH resources and the design of safe and effective exploration strategies.

Long-distance in-situ near-infrared gas sensor system using a fabricated fiber-coupled Herriott cell (FC-HC) operating within 1.5–2.3 μm

Long-distance field gas sensing in hazardous environment is highly desirable in industry but remains challenging due to ultralow concentration levels of the target gas species. A fiber-coupled Herriott cell (FC-HC) was fabricated for long-distance gas detection, which is composed of a sealed Herriott cell with a dimensional size of 8.3 cm × 9.0 cm × 47.2 cm, a single-mode fiber collimator for input light coupling and a multi-mode optical fiber for output light coupling. The experimentally measured absorption path length of the FC-HC is ∼24.6 m through acetylene (C2H2) detection. Also, this FC-HC is compatible with distributed feedback lasers operating from ∼1.5 μm to ∼2.3 μm. C2H2 and methane (CH4) measurements were carried out using the fabricated FC-HC. The measurement precision of C2H2 is 0.38 parts-per-million in volume (ppmv) with a 0.5 s averaging time, which can be further decreased to 27.20 parts-per-billion in volume (ppbv) with a 70 s averaging time. The limit of detection (LoD) of CH4 is 1.11 ppmv with an averaging time of 0.5 s and can be improved to 0.04 ppmv with an averaging time of 122 s. Field measurement of the sensor system for in-situ CH4 leakage was performed to validate the normal operation of the system. The proposed FC-HC shows potential applications in the field of long-distance gas sensing based on laser absorption spectroscopy.

Long-distance free space gas detection system based on QEPTS technique for CH4 leakage monitoring

Based on the quartz tuning fork enhanced photothermal spectroscopy (QEPTS) technology, a long-distance free space gas detection system was proposed to monitor CH4 leakage. A CH4 absorption line at 1650.961 nm was selected for this gas detection system to reduce the interference of water vapor and carbon dioxide in the atmosphere. The Allan deviation analysis showed that the integral detection limit of this long-distance free space gas detection system for CH4 detection could reach 3.79 ppb·m at the optimal integration time of 502 s. And the linear response of the proposed sensor was evaluated, with yielded R-square value of 0.997 being obtained. In addition, a CH4 cylinder with concentrations of 5% was placed in different positions to simulate the leakage of CH4 in free space, and the experimental results showed that the long-distance free space with a QEPTS gas detection system could meet the need for CH4 leakage detection in the practical engineering application.

Application of long short-term memory recurrent neural networks for localisation of leak source using 3D computational fluid dynamics

Gas leaks represent a major concern in industrial sites due to potential human and economical losses. Prompt identification of leak scenarios favours corrective maintenance avoiding the domino effect. In this paper, long short-term memory recurrent neural networks were trained and tested to CH4 leakage source in a chemical process module. We exploit the benefits of varying the temporal length of input variables, and the datasets were obtained employing 3D-CFD simulations. We consider four leak locations, four wind speeds, and eight wind directions, besides the non-leakage scenario for the same wind speeds and directions. The models were trained using different values of timesteps to evaluate the prediction accuracy for unseen data. Results showed progressive improvement of the performance of the models with greater values of timesteps, and good generalisation with test accuracy over 95.3%, indicating the ability of the model to correctly predict the leakage source using easily monitored variables.

Capillary Heterogeneity Linked to Methane Lateral Migration in Shallow Unconfined Aquifers

AbstractWe investigate mechanisms that enhance lateral methane (CH4) plume migration in shallow aquifers that exhibit complex and multiscale sedimentary architecture. We show how heterogeneity in capillary pressure characteristics related to the sedimentary architecture causes gaseous CH4 to spread over larger areas by retarding, deviating, or blocking upward buoyancy‐driven CH4 migration. Simplifying or ignoring capillary pressure heterogeneity thus leads to overestimation of leaked CH4 to the atmosphere, and underestimation of mobile gaseous CH4 in aquifer. We show, both qualitatively and quantitatively, that meter‐scale sedimentary stratification contributes more to CH4 plume migration than the millimeter‐ and centimeter‐scale strata comprising them. Results indicate that the extent of gaseous CH4 leakage, and its associated impacts on groundwater quality and global warming, cannot be accurately assessed unless the sedimentary architecture and resulting heterogeneity in capillary pressure are represented.

Are seep carbonates quantitative proxies of CH4 leakage? Modeling the influence of sulfate reduction and anaerobic oxidation of methane on pH and carbonate precipitation

Seep carbonates tell us where and when CH4-charged fluids escaped from the subsurface, thus providing qualitative information to reconstruct the activity of petroleum systems. The potential of seep carbonates as quantitative proxies for the amount of CH4 leaked, however, remains largely unexplored, which limit their applicability as exploration tools. This paper tackles the quantification of the CH4 flux - seep carbonate relationship by simulating the coupled sedimentary carbon (C) – sulfur (S) cycles in a reaction-transport modeling (RTM) framework. We first establish a theoretical basis demonstrating that the stoichiometry of diagenetic reactions and the ambient pH of pore waters are the main drivers of the rate of change in the saturation state of carbonate minerals (ΩCal), while the concentrations of total dissolved inorganic carbon and sulfide are only of secondary importance. It results that anaerobic oxidation of methane (AOM) is the main driver of carbonate precipitation, while organoclastic sulfate reduction (SR) has a minor impact. We further show that SR mostly drives carbonate dissolution, but can also contribute to precipitation when pH is low (<7–7.1). The RTM simulations reveal that an increase in upward fluid flow triggers an intensification of peak AOM rates, associated to a shallowing and thinning of the zone of carbonate precipitation. Such behavior leads to an almost linear relationship between the amount of carbonate precipitated and flux of CH4 (nCH4 = 3.3–5.2 * nCaCO3), until, eventually, full cementation occurs. We thus define a “quantitative domain” at moderate fluid flow and a “threshold domain” at high fluid velocities, where full cementation solely provides a lower bound estimate of the amount of CH4 leaked. We also show that in contrast to a traditional view of seep carbonate formation mainly controlled by venting activity, sedimentation rate and water depth also play major roles, via their control on residence time and saturation concentration of CH4, respectively. The interpretation of vertical seep carbonate stacks should thus not solely focus on changes in fluid flow, but also consider changes in sedimentation rate and/or water depth.

Long-distance in-situ methane detection using near-infrared light-induced thermo-elastic spectroscopy

A wavelength-locked light-induced thermo-elastic spectroscopy (WL-LITES) gas sensor system was proposed for long-distance in-situ methane (CH4) detection using a fiber-coupled sensing probe. The wavelength-locked scheme was used to speed the sensor response without scanning the laser wavelength across the CH4 absorption line. A small-size piezoelectric quartz tuning fork (QTF) with a wide spectral response range was adopted to enhance the photo-thermal signal. The optical excitation parameters of the QTF were optimized based on experiment and simulation for improving the signal-to-noise ratio of the LITES technique. An Allan deviation analysis was employed to evaluate the limit of detection of the proposed sensor system. With a 0.3 s lock-in integration time and a ∼ 100 m optical fiber, the WL-LITES gas sensor system demonstrates a minimum detection limit (MDL) of ∼ 11 ppm in volume (ppmv) for CH4 detection, and the MDL can be further reduced to ∼ 1 ppmv with an averaging time of ∼ 35 s. A real-time in-situ monitoring of CH4 leakage reveals that the proposed sensor system can realize a fast response (< 12 s) for field application.