As you know, this concludes all efforts under the existing contract. All further system investigations and improvements will be addressed under the Field Testing Program. We are completing our efforts toward developing a Field Program cost estimate, and I will forward that to you shortly.
We at Chimera and OPHIR are looking forward to the Field Program. To our knowledge, no comparable open-path spectrometer has ever been previously developed. Therefore, this DIAL System offers capabilities never before achievable in the field. And, we continue to investigate atmospheric and geochemical processes and lidar hardware never previously explored. Thus, the Field Program will be a significant technological accomplishment, and will require significant effort and "hands on" learning. Indeed, the entire methodology of oil and gas prospecting using this unique tool must be developed. This will be a significant focus of the Field Program.
As we have stated previously, we fully support your efforts to both develop and deploy this unique technology, Thank you for your support of this project.
Sincerely,
Chimera Geophysical Corporation
Martin O'Brien
President
Enclosure
Final Report: Hydrocarbon DlAL Development Effort
Introduction
This report provides a summary of all activity performed under the Hydrocarbon DIAL System Development contract. It provides a brief summation of the Controlled Release Test results, and
enumerates the technological accomplishments to date. This report concludes all activity under the said contractual effort.
This effort began 3 July 1997. The contract objective was to develop and demonstrate a Hydrocarbon Differential Absorption Lidar (DIAL) System capable of detecting atmospheric ethane and methane in the open atmosphere, to an optical pathlength of 2 miles (1 mile laser-to-reflector distance). Propane was to be explored to investigate the potential for open path atmospheric monitoring. The DIAL System is mounted in an 18 foot long trailer and is wholly self contained and portable to remote field sites. All contract objectives have now been successfully completed. Moreover, the System performance was successfully demonstrated during the Controlled Release Test of 23 June 1998.
The Hydrocarbon DIAL consists of a Raman-shifted Cr:LiSAF laser to generate the spectroscopic probe beam. Precise spectral tuning is accomplished with an extended cavity solid state diode laser. The performance of this seed laser has been proven to be outstanding. Repetitive, consistent and rapid spectral scans can now be achieved under software control. This is a significant and enabling technology that greatly improves DIAL System performance and utility in the field. As with OPHIR's previous laser systems, the DIAL uses an oscillator/amplifier Cr:LiSAF laser configuration. The oscillator and amplifier amplify the seeder laser wavelength to sufficient power levels to achieve Raman-shifting in hydrogen gas. A new Raman cell was designed, manufactured and assembled for this effort. The new cell performance has been investigated and is performing as anticipated. As the laser light passes through the Raman cell, the laser wavelength is shifted into the 3.3 µm spectral region. All shorter wavelength light is contained within the trailer, resulting in an eyesafe system at the exit aperture of the trailer. A collinear transmitting/receiving geometry is used for the laser beam transmission and reception telescope. Light to and from the lidar is directed in azimuth and elevation with a two-axis goniometer stage mounted on the roof of the trailer. The transmitted laser light is sent to a remotely-located retroreflector. Trailer to reflector distances of up to a mile are achievable. A 1 mile distance (2 mile optical path) was successfully demonstrated during the 23 June Controlled Release Test. The System design has been previously disclosed, and was presented at the System Design Review of 13 February 1998.
23 June 1998 Controlled Release Test
The Hydrocarbon DIAL System is now operational. System performance testing began on 4 June 1998. Testing has been completed on all aspects of the hardware. This includes: seed laser performance, Cr:LiSAF oscillator and amplifier performance, Raman cell alignment and performance, beam steering and optical alignment, retroreflector performance, signal collection system performance and data logging system performance. Although minor system improvements have been identified, the DIAL System is performing at or above the anticipated level. The system's ability to select and scan specific trace gas spectroscopy features is outstanding.
To demonstrate and document the Hydrocarbon DIAL System performance, a Controlled Release Test was performed on 23 June 1998 at the Fort Morgan Municipal Airport, Fort Morgan Colorado.
The test consisted of operating the lidar solely on generator power while detecting methane and ethane over a 1 mile laser-to-reflector distance.
The Controlled Release Test focused on, and was successful in detecting, methane and ethane. The test methodology consisted of positioning the retroreflector at a 1 mile distance from the laser trailer. Next, a 2 meter long sheet metal tube with polyethylene windows was positioned in front of the retroreflector, also at a 1 mile distance. The tube was first filled with the local atmosphere, then with a mixture of 8000 ppm methane and 800 ppm ethane. These concentrations provide an equivalent optical absorption as would be measured from an atmosphere containing 10 ppm methane and 1 ppm ethane. That is, the Controlled Release Test verified the DIAL System's performance for monitoring an evenly distributed atmospheric concentration of
10 ppm methane and 1 ppm ethane. Atmospheric background wavelength scans demonstrated the System's ability to monitor background concentrations of methane (approximately 1.8 ppm methane).
Wavelength scans of specific methane and ethane spectral signatures were then performed. Data were gathered to document these spectral scans. A full summary of this data will not be presented here. Rather, select summaries are provided to document the System performance. Figure 1 provides a scan of ethane at the 1 ppm atmospheric equivalent level. Here a strong and obvious ethane absorption was detected. FASCODE/HITRAN modeled output has also been included in the figure as a solid line. (DIAL System measurements are shown as dots.) Roughly a 40% signal
absorption can be attributed solely to the presence of 1 ppm atmospheric ethane. The spectral features agree very well with the FASCODE/HITRAN theory, demonstrating that the system is functioning as expected and is properly tuned to ethane.
Figure 2 provides similar data for methane. In this case, however, the tube was not filled with the hydrocarbon test gas. Rather, this figure demonstrates that the DIAL System can readily monitor background atmospheric methane. Roughly a 30% signal absorption can be attributed to background methane. The figure also indicates that the background methane concentration at Fort Morgan on 23 June was very likely less than the U.S. Standard Atmosphere background level for methane. That is, the system can readily monitor atmospheric methane, roughly 1.8 ppm methane. Again, the spectral features agree well with FASCODE/HITRAN theoretical model, confirming the system operation. It is interesting to note that the 10 ppm methane gas sample resulted in the return beam being nearly entirely absorbed. This dearly demonstrates the sensitivity of the system. Future efforts will concentrate on which spectral feature to use for very high levels of atmospheric methane.
Propane spectroscopy was performed in the laboratory environment and disclosed previously. During those investigations, it was determined that propane can be detected, in the field, in lower humidity atmospheres. Atmospheric water vapor has molecular absorption features coincident with those of propane. Heavy rain, and the resultant high atmospheric humidity, prevented propane investigations during the Controlled Release Test. Further open-path measurements, over a broad range of humidity conditions, will be required to characterize the System's ability to monitor propane. Thus, we will continue to explore propane spectroscopy in future efforts.
Conclusions
With the successful conclusion of the Controlled Release Test, the following statements can now be made regarding this technology.
©1998, Chimera Geophysical Corporation, all rights reserved
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