Portable Laser Gas Detector Systems for Greenhouse Gas Emissions and Monitoring in Oil and Gas Operations
Hamish Adam , Chris Parker
Boreal Laser Inc.
#13, 51127 RR 255,
Spruce Grove, AB T7Y 1A8, Canada
hadam@boreal-laser.com
John Tulip
ECERF,
University of Alberta
Edmonton, Alberta, Canada
Keywords
Tunable Diode Lasers, TDL, Emissions Monitoring, Portable, Greenhouse Gases, CO2, CH4
Abstract
Two types of portable laser based gas detector for measuring emissions of the greenhouse gases carbon dioxide (CO2) and methane (CH4) from oil and gas operations are described. A scanning open path detector was developed within a Cooperative Research and Development Agreement (CRADA) with the USEPA. This system scans multiple paths across an area source in rapid succession, enabling calculation of concentration profiles and emissions fluxes. A vehicle mounted detector acquires ambient CH4 or CO2 data with excellent concentration and spatial resolution. The long wavelength laser used enables CO2 resolution of 5 ppm. Field data from both types of detector are presented.
Introduction
There has recently been a significant increase in interest in detecting and quantifying emissions of the greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4) from oil and gas operations – both in Alberta and other jurisdictions in North America and Europe. The primary drivers for this increased interest are: new and pending legislation requiring demonstrated reductions in GHG emissions from oil and gas facilities; financial incentives in the form of emissions trading credits; strong interest in CO2 sequestration in abandoned oil and gas reservoirs as a technique for CO2 emissions reduction.
A major barrier to effective implementation of emissions reduction and trading plans is the absence of real emissions measurements to establish baselines and confirm reductions (1). This is especially true for fugitive emissions from area sources comprised of distributed or multiple point sources such as natural gas production and processing facilities in Alberta. Several oil and gas company personnel responsible for GHG emissions inventories and reductions have recently complained that traditional point monitoring technologies and emissions bagging schemes are either too laborious, too expensive or provide insufficient coverage to enable cost effective continuous monitoring.
Two new measurement systems based on laser gas detection have been developed in conjunction with industry and government partners to meet these monitoring needs. Laser based gas detectors using room temperature tunable diode lasers (TDL) are well established for many critical safety, environmental and process monitoring applications. The laser technique has several distinct advantages over traditional gas detection techniques (2, 3). It uses single line absorption spectrometry in the near infrared, which results in a direct measurement of the gas of interest with no cross interference from other gases. The absence of water vapor interference enables long open path ambient monitoring – up to 1 km. Response times of less than 1 second are possible. The specific laser detector designs described here have the added benefits of being self calibrating, portable and robust. With no moving parts and no consumables, maintenance costs are very low.
TECHNOLOGY DEVELOPMENTS
SCANNING TDL PLATFORM
A portable, high precision, scanning open path TDL spectrometer has been developed by Boreal Laser through a Cooperative Research and Development Agreement (CRADA) with the US Environmental Protection Agency. The driving force for this joint development was the desire for a practical method to enable determination of emission fluxes from area sources. This scanning open path TDL system consists of the GasFinder2 TDL spectrometer (4) mounted on a precision scanning platform that is controlled by a host computer using motion control software. Figure 1 shows the components and interconnectivity of the scanning TDL system. The TDL spectrometer is a combined transmitter and receiver (transceiver) which relies on a reflector to return the laser light to spectrometer for real time analysis. The reflector distance from the spectrometer defines the system path length, which can be between 10 cm to 1 km. The wavelength modulation technique (3) used to achieve maximum sensitivity normally requires a phase matching that must be repeated every time the path length is changed. The system described here employs a “No Phase Adjustment” detection technique (4) that removes the need for this procedure. This enables the TDL spectrometer to scan through any number of paths of various lengths with no path length compensation – a unique feature of this particular system.
Figure 1: Scanning Open Path TDL spectrometer
The programmable scanner has 360° of horizontal movement and 120° of vertical movement with a step precision better than 0.006° per step. The robust packaging of the system allows it to operate from -30 Dec C to 50 Dec C in rain, snow, or fog – provided that visibility remains good enough for sufficient laser energy to traverse the measurement path. The system can tolerate a factor of 20 turn-down in transmitted light energy from ideal conditions before a “low light” condition occurs. The scanning system can be programmed to scan up to 36 different paths in succession. Typically, the system will measure on one path for between 10 and 60 seconds before moving to the next path. Transition time between paths is normally 2 or 3 seconds. Successive path averaged concentrations are fed back to a central logging computer. The computer is also configured to accept wind speed and wind direction data to enable flux measurements to be calculated. The computer can then use one of several commercially available algorithms to compute concentration profiles and emissions fluxes from the multiple path averaged concentration data. This scanning system has been used most often with the Radial Plume Mapping (RPM) algorithm (5) and which forms the basis of the EPA’s recently promulgated Open Path Monitoring (OPM) method OPM-10 (6, 7). The scanning multiple path method is currently being tested with other deterministic and stochastic algorithms (8, 9).
VEHICLE MOUNTED TDL GAS MONITOR
A fiber-coupled laser gas analyzer that can be coupled to different measurement probes for open path, process or duct monitoring has been previously described (10). The system is a variation configured for vehicle mounted monitoring applications as shown in Figure 2. This configuration has been used for over 10 years in a helicopter mounted arrangement for the reliable detection of CH4 leaks from high pressure natural gas pipelines.
Figure 2. Schematic of vehicle mounted laser gas analyzer
During the past 2 years, the airborne system has been adapted with different sensing probes for ground based CH4 and CO2 monitoring with road-going and off-road vehicles. The features of the vehicle mounted system are summarized in Table I.
TABLE I: SPECIFICATIONS OF VEHICLE MOUNTED TDL GAS MONITOR
|
Parameter |
Airborne System |
Ground based system |
|
Precision |
<1 ppm (CH4) |
0.2 ppm (CH4); 5 ppm (CO2) |
|
Full scale |
100 ppm (CH4) |
500 ppm (CH4); 10,000 ppm (CO2) |
|
Data rate |
3 readings per second |
1 reading per second |
|
GPS |
Built-in |
Built-in |
|
Recommended speed |
60 – 100 knots |
20 – 100 km/h |
|
Total system weight |
20 kg |
20 kg |
|
Power source |
Helicopter 28Vdc |
Vehicle 12Vdc |
HIGH RESOLUTION CARBON DIOXIDE LASER GAS DETECTOR
Room temperature tunable diode lasers for use in instruments such as those described here were only commercially available to about 1800 nm until recently. Earlier studies of CO2 therefore used a relatively weak IR absorption band near 1580 nm. This resulted in a resolution of 500 ppm-m at best. Path lengths of 100m to 200m are typical of oil and gas facilities which converts to approximately 1% of reading (average 380 ppm concentration multiplied by path length of 100m yields 38,000 ppm-m). Computer simulations indicate that resolution closer to 0.1% is required in order to detect the small increases from background CO2 that could be produced by leaks from CO2 injection projects, for example. Room temperature diode lasers near 2000 nm have recently become commercially available, enabling the use of CO2 absorption lines in this spectral region which are 10 to 50 times stronger. Using these new lasers in the vehicle mounted configuration provides 5 ppm sensitivity. It has been determined that 50 ppm-m sensitivity is optimum for open path monitoring with respect to enabling reasonably long path lengths to 150m before onset of instrument saturation – but still enabling reading resolution of 0.1 to 0.2 % over such paths.
METHANE AND CARBON DIOXIDE EMISSIONS MONITORING IN OIL AND GAS
The systems described are currently deployed on a number of emissions monitoring projects and trials with oil and gas companies and research organizations. A primary purpose of these trials is to compare the accuracy of different algorithms used for analysis of multiple open path or multiple point data in two respects:
- Triangulating leak sources within area or multiple source facilities.
- Calculating emission fluxes across fence lines.
Trials have been designed to arrange controlled releases of known mass flow rate from known locations. Recent testing of the new high resolution open path CO2 system with the Alberta Research Council (ARC) has yielded promising results with regard to sensitivity compared with earlier open path CO2 systems. Early indications are that this may be a useful tool in area monitoring for CO2 leak detection in CO2 sequestration projects. Further trials are planned with other research bodies in the US and Europe. This work is confidential and data are not yet available. However, the superior performance of the laser gas detection systems can be demonstrated using data from other, earlier implementations.
Airborne detection of leaks from Natural Gas Pipelines
A helicopter mounted version of the system shown in Figure 2 has been used with great success for over 10 years to detect CH4 leaks from high pressure natural gas transmission lines in Canada (with TCPL), USA, Russia, Thailand and other countries. Recently, the US Department of Energy completed testing of this system over simulated leaks from their test pipeline at the Rocky Mountain Oilfield Test Center in Wyoming. The study concluded that “The system had no “down-time” and remained operational throughout the three-day test. Compared with the previous tests, this airborne methane detection system produced substantial improvement in gas leak detection making it a viable system for gas leak detection in the field.” (11).
Ground based detection of Natural Gas leaks and seeps
Both truck mounted, road going and all-terrain-vehicle (ATV) mounted, off road CH4 laser leak detection systems have been successfully used in Alberta during the past 2 years for rapid area coverage in the detection of leaks from medium pressure natural gas pipelines and production and processing operations. One example is shown in Figure 3. Canadian installations have also used both airborne and ATV mounted CH4 laser systems to detect elevated ambient levels of CH4 from underground seeps as an exploration aid.
Figure 3. Ground based detection of CH4 leak. The initial “hit” was detected traveling at 110 kph on the highway
Landfill CH4 monitoring
Experience gained in the use of the CH4 laser systems to identify and quantify CH4 emissions from landfills is instructive for describing how the systems will be used for similar applications in oil and gas operations. Landfills represent roughly 13 percent of global CH4 emissions. Until recently, the methods of determining methane flux were time consuming and based largely on estimation. The recently published EPA Method OM-10 (7) enables scanning laser open path measurements to be used in conjunction with Radial Plume mapping (RPM) algorithms to characterize CH4 emissions from landfills.
The configuration for emissions flux measurement requires that the scanning laser system is set up to define a flux plane through the use of multiple ground and elevated reflectors within a vertical plane at the downwind boundary of a study area. Vertical RPM analysis of the multiple path integrated concentrations yields a vertical CH4 concentration profile (see Figure 4). Integrating wind speed and direction data allows determination of total CH4 flux through the boundary plane. An alternative horizontal scanning configuration, using multiple reflectors deployed across or around the landfill enables Horizontal RPM analysis to generate horizontal CH4 concentration profiles and identify leak sources or “hot spots” (Figure 4). A landfill is sectioned into manageable sections, and the survey equipment can effectively be used to determine flux emissions from different cells within the landfill.
Figure 4. Landfill METHANE emissions generated by a scanning TDL spectrometer system and Radial Plume Mapping with Vertical RPM on the left and Horizontal RPM on the right.
The ATV mounted CH4 laser system has also been successfully used for rapid surveying of landfills in Europe to quantify emission fluxes and pin-point leak sources.
CO2 sequestration monitoring
CO2 Sequestration is proposed as a solution for reducing the emissions of CO2 from large scale industrial processes, such as Oil Sands operations and coal-fired power generation in Alberta. CO2 emissions are captured and injected into underground geological formations, typically depleted oil and gas reservoirs. However, CO2 sequestration can only be considered effective if the CO2 remains captive. The technique relies on the integrity of cap rock overlying the storage reservoir to prevent leakage of injected CO2 to the atmosphere. This has recently become a topic of considerable discussion (12). Reservoir cap rock is typically perforated with tens or hundreds of holes during the reservoir’s productive life. There is a probability that not all these holes have been completely sealed. Fortunately, existing CO2 injection enhanced oil recovery projects provide surrogate real-life experiments with which to test the hypothesis of CO2 sequestration. Research bodies such as ARC and British Geological Survey (BGS) have conducted several soil CO2 surveys on large scale CO2 injection projects such as the Weyburn Project in Saskatchewan (13). Traditional measurement techniques such as soil sampling are far too time consuming and localised to enable time- and cost-effective surveying of CO2 injection sites. Hence, both BGS and ARC have recently conducted trials of the scanning and vehicle mounted laser systems in order to demonstrate their superior effectiveness for leak detection in CO2 injection.
Emissions in volcanic regions of the world also enable development and testing of methodologies for CO2 sequestration monitoring. Early studies with the low resolution (1000 ppm-m) 1580 nm CO2 system on CO2 injection projects were typically unable to distinguish small leaks due to the high level of CO2 background (about 380 ppm) and the relatively poor CO2 sensitivity. However, in situations where there were high levels of CO2 emissions, such as volcanic pools in Italy, the technique worked very well (14).
BGS has validated a vehicle mounted high resolution CO2 system in volcanic geologies in Italy and Germany. Figure 5 shows data from a survey on the edge of a caldera lake in the Eiffel region of Germany. This survey identified the location of CO2 plumes not previously known. BGS is currently working on the development of EU protocols for CO2 sequestration monitoring using the vehicle mounted high resolution CO2 laser system.
Figure 5. Ground level CO2 map on edge of caldera in Eiffel region of Germany generated with ATV mounted TDL system
CONCLUSIONS
Laser detectors have many advantages over established gas detection techniques in process, quality, safety and environmental monitoring. They do not suffer from interferences. They provide fast response and can measure a wide range of concentration values. On-board calibration, and maintenance-free operation dramatically reduces long-term cost of ownership. Laser gas analyzers are replacing traditional gas analyzers and detectors in a growing number of applications across a broad spectrum of industries as a result of these advantages.
Portable laser gas detector systems have been developed in collaboration with industry to meet the unique measurement challenges presented by the need to identify leaks and determine fluxes of the greenhouse gases CO2 and CH4 from area sources in oil and gas operations. Field experience with the laser gas detectors in similar application configurations has confirmed that these systems enable significant improvements over traditional monitoring techniques. Initial results from trials currently underway at oil and gas facilities reinforce that the systems described will have unique roles to play in quantifying emissions reductions from area sources in oil and gas operations.
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