Emissions from flares – including climate-damaging methane – could be underestimated, according to new research published today.
The Environment Agency has assumed that flaring waste gas on onshore hydrocarbon sites was the best practice for protecting the environment.
But the regulator has conceded that evidence to support this conclusion was limited.
It said there were few measurements of how much unburnt gas was emitted that could harm the environment and may contribute to global warming.
A study for the EA by the National Physical Laboratory concluded:
“unburnt hydrocarbons from flares can be elevated, implying that combustion can be inefficient. This means that if flare emissions are estimated by assuming efficient combustion of hydrocarbons, then actual emissions may be underestimated – including methane.”
The study, one of six research projects on the onshore industry released today, found that combustion efficiency at four case study sites varied from about 85%-99%, depending on the flare and stage of operation.
It found a “tendency for higher emissions of unburnt hydrocarbons to occur under conditions of low [gas] flow”. Hydrocarbons could also be released during non-operational periods from leaking gas valves, the study concluded.
The authors recommended that site operators should keep full records of relevant flare types, flows, inlet gas compositions and operating conditions.
Another study found short-comings in software used by fracking companies to predict fractures in shale rock.
Computer models are a key part of hydraulic fracture plans, which are used to regulate operations.
But the study author, the British Geological Survey (BGS), concluded that different software and modelling approaches produced different results using the same inputs.
Relying on hydraulic fracture simulators alone as proof of compliance – particularly in new shale gas areas – was not feasible, the study said.
The authors found that hydraulic fracture stimulation software was now more capable and accurate than a few decades ago.
But they said the sophistication of the software varied. Most was limited to modelling simple fractures, despite growing evidence that induced fractures were more complex.
The research also showed that very few commercially-available simulators were capable of coupling hydraulic fractures with the existing natural fracture network. But the study said this was essential to accurately assess the connectivity of the hydraulic fracture network.
The study recommended that regulators should consider whether the input parameters used in hydraulic fracturing proposals were reasonable for the expected formations, fluids and stress conditions.
It also said hydraulic fracturing activities should be monitored as they progressed, and the models refined to improve their accuracy and as proof of compliance with permits.
A more comprehensive review should be carried out and key issues, such as stress and rock properties, should be quantified.
Other studies released today looked at:
- impact of leaks from abandoned wells on groundwater quality
- methods for analysing air quality and groundwater data near oil and gas sites
- identifying fracking-induced earth tremors
Key points from studies
Title: Review of differential absorption using LiDAR flare emission and performance data
Purpose: Review data on how well waste gas is burned in flares
Method: Light Detection and Ranging (LiDar) remote sensing technique, known as DIAL (differential absorption). The EA said this technique shines a laser into the flare and records the wavelengths, intensities and timings of the reflected light which indicate the composition, concentration and position of the gas. This can be used to evaluate the combustion efficiency, and the amount of unburnt methane and other air pollutants released to atmosphere. The technique measured emissions of hydrocarbons, sulphur dioxide and NOx.
Key findings: The four case studies, which included what was described as “a conventional onshore oil extraction site”, did not provide enough examples for a comprehensive analysis of flare emissions performance covering different types of flares, flows, hydrocarbon compositions and operating conditions.
But the project concluded:
- Emissions and combustion efficiency can vary from about 85%-99% depending on the flare and stage of operation
- Tendency for higher emissions of unburnt hydrocarbons under conditions of low flow
- Gas valves may leak so hydrocarbons are released during non-operational periods
- Frequent gaps in supporting data on flaring provided by operators
- DIAL can quantify emissions of gases but operators should also keep full records of relevant flare types, flows, inlet gas compositions and operating conditions
Authors: National Physical Laboratory
Title: Review of software used by the oil and gas industry to model hydraulic fracturing
Purpose: Review computer models used by oil and gas industry to understand how fractures extend underground. The Environment Agency said it needed to know what the models do, how they operate and how they help to assess environmental risk at individual sites.
Method: Literature review of commercially available software for hydraulic fracturing and catalogue of main features.
Key findings: Seven modelling packages identified had different levels of sophistication and provide different results.
- Some models did not simulate the effects of induced fractures on the existing fracture network.
- Regulators should consider whether input parameters used in hydraulic fracturing proposals are reasonable in the conditions and operations expected
- Hydraulic fracturing activities should be monitored and models refined to improve accuracy
- More comprehensive review should be carried out
- Stress and rock properties expected in shale gas fields should be quantified
Author: British Geological Survey
Abandoned wells and groundwater
Title: Impacts on groundwater quality from abandoned hydrocarbon wells
Purpose: Evidence from the USA shows hydrocarbon wells have had an impact on some shallow groundwater, mainly because of well integrity or poorly constructed wells. Previous studies have showed evidence of limited methane emissions to air from abandoned UK oil and gas wells. The project aimed to better understand whether abandoned deep wells have leaked and what would be the impact on groundwater quality.
Method: Reviewed records of 2,000 UK onshore oil and gas wells to identify those most likely to impact on groundwater. Selected two former gas wells (Nooks Farm, Staffordshire and Ashdown, Sussex) and two former oil wells (Hemswell, Lincolnshire and Lomer, Hampshire) for field investigation. Two rounds of sampling collected a total of 48 groundwater samples. The study used existing groundwater boreholes and no dedicated monitoring boreholes were installed near the study sites.
- Low concentrations of hydrocarbons were found in groundwater.
- High maximum dissolved methane concentration of 407 ug per litre was found in the first sampling round but not repeated in the second.
- Volatile organic compounds, polyaromatic hydrocarbons, pesticides, herbicides, fungicides, surfactants, analgeisics and veterinary compounds were found in some samples at low concentrations. None could be linked unequivocally to abandoned wells.
- Soil gas survey at Ashdown and a new study location (Bolney, Sussex) produced ambiguous results with elevated concentrations of carbon dioxide and methane.
Authors: British Geological Survey and Environment Agency
Risks to deep groundwater
Title: 3D groundwater vulnerability
Purpose: Examine sources of groundwater deep below surface and assess its vulnerability to pollution.
Methodology: Assessment of the risks of subsurface oil and gas activities to groundwater at different depths in five case study sites across England.
Key findings: Most of the aquifers studied were found to be at low risk of contamination. Some were medium-low or medium-high risk. None were found to be at high risk.
Author: British Geological Survey
Monitoring air and groundwater quality
Title: Onshore Oil and Gas monitoring: assessing the statistical significance of changes
Purpose: Identify methods for analysing air quality and groundwater monitoring data near onshore oil and gas sites. This will help define baselines and show how changes from the baseline may be detected.
Key findings: Advice on procedures for monitoring survey design and data analysis, with appropriate statistical tests.
Author: Environment Agency
Identifying fracking-induced earth tremors
Title: Guidance on seismic cluster definition and identification
Purpose: Investigate a statistical approach known as clustering to distinguish seismic events induced by fracking from background everyday seismicity. Real time analysis of clustering of seismic events could help to indicate the onset of fault reactivation and allow early intervention.
- The approach could be used to detect and cluster unusual seismic activity as long as the events were more than about 450m from the main seismic cluster.
- The method is promising and may be worth further work to develop bespoke software.
- It could also be used to test the effectiveness of clustering methods as early indicators of problems in fracking operations.
Author: Professor Peter Styles, Calculus Geoscience Consultants Ltd
Updated 23/10/2019 to include details of sixth report