InSAR, no longer under the radar.
My last blog post talked about the future of borehole seismic being in Distributed Acoustic Sensing (DAS) and the promise of reduced rig time and HSE exposure. As the digital transformation of the energy sector accelerates there will be increasing pressure to further improve operational efficiency and ESG standards through increased automation and remote operation.
This blog will focus on an extension of those ideas to a fully remote sensing technology, InSAR.
This is an extremely exciting subject area, at the forefront of scientific research and highly relevant in today’s low carbon environment.
This blog will be in two parts; a general chat about what the technology is and what it can bring to the energy sector followed by a more specific post about using InSAR data in unconventionals to try to address the “unbalanced mass balance” in unconventional stimulation and to potentially gain independent insight into stimulated volume and stage efficiency.
Somewhat refreshingly, there has been a lot of news coverage this week on the launch of the first SpaceX dedicated rideshare mission. The idea is to utilize a two-stage reusable rocket, the Falcon-9, to deploy satellites from fee paying third parties into orbit. An orbital Uber. The launch on January 24th delivered 143 satellites, the most ever, some as small as an iPad. They covered an array of applications from IoT monitoring to communications and, of particular interest, earth observations satellites including two new SAR satellites from Capella Space; Capella-3 and Capella-4.
InSAR is a satellite technology (utilizing SAR satellites) used for measuring surface deformation, how much the ground surface rises or falls due to sub surface volume changes caused by fluid (or gas) injection or extraction. With ongoing improvements in temporal and spatial resolution, changes in the order of a millimeter/year can be measured. Both vertically and in the west-east direction.
InSAR (Interferometric Synthetic Aperture Radar) is a way to measure small changes in land surface elevation from Earth’s orbit. It utilizes SAR satellites which emit microwave radar signals typically with wavelengths between 2.4 cm and 30 cm. Data from several observations are combined to create a dataset with the large, required aperture to achieve the high spatial resolution desired, hence the term ‘synthetic’. This is not, so I am told, strictly analogous to stacking seismic traces, but close enough for me.
A distance from the satellite to the land surface is calculated by measuring the two-way reflected travel time (sound familiar?). This distance is calculated again at a later time and another distance calculated, the difference (interference) between the two distances is represented as an interferogram. Vertical and lateral displacement can be determined using different processing techniques.
A Falcon 9 carrying 143 satellites launches from Cape Canaveral, Florida, on January 24, 2021
Credit: Carleton Bailie
The electromagnetic spectrum with microwave bands inset.
Credit: NASA SAR Handbook.
Geometry of observations used to form the synthetic aperture for target P at alongtrack position x = 0.
Credit: NASA SAR Handbook.
I should emphasize that this is a satellite technology, no land-based personnel or equipment is required. The satellites are in continuous orbit providing a constant stream of data and have been doing so for many years (the earliest SAR satellite, SEASAT, was launched in 1978). No bespoke data acquisition is required, data is available from the past, in the present and will be increasingly available in the future. I could imagine plenty of opportunities to ‘look back’ at InSAR data over the years in the context of, for example, EOR projects. In some cases InSAR could provide an alternative to surface tiltmeters.
To learn more, I would recommend a free Udemy course from PCI Geomatics, Advance SAR Training which you can find here.
So, where can this technology be useful in the energy sector. Rucci et al (2018) identifies several applications of InSAR monitoring services to the energy industry.
(1) highlight zones of excessive pressure variations and check for out-of-zone fluid migration
(2) optimize production strategies
(3) provide information to assess well integrity
(4) reduce uncertainties about reservoir behavior
(5) calibrate geomechanical models
(6) facilitate HSE regulatory compliance and safety levels.
Remember that implicit to InSAR is the time lapse component with updates available every few days.
The recent edition of The Leading Edge (January 2021, Volume 40, No. 1) has a special section on remote sensing with several excellent papers. Dubucq et al give a really interesting overview of various Earth observation satellite methods, including InSAR. In the same edition Rahmoune et al present a fascinating case study from Oman. They highlight an important feature of InSAR, the need for stable reflectors which do not change during the observation period and which provide stable backscattered energy. This is the main reason why InSAR might struggle in areas of snow cover or thick vegetation. In other words, perhaps not ideal for the oil and gas fields of Alberta, Canada but ideal for the Permian basin.
One of the case studies presented by Rahmoune et al looks at a heavy oil field under steam flood for the last ten years or so. Field wide deformation monitoring using InSAR to map steam front development has been a crucial risk mitigation tool to help prevent steam breakthrough into producing oil wells. This surface movement shown below has been corelated with active fault movement at the reservoir level indicated by the occurrence of microseismic events. Wouldn’t it be interesting to supplement these data with a crosswell seismic profile across the area of highest deformation in the northern section?
Surface deformation map (mm), 2010-2020 (Rahmoune et al, 2021).
Using InSAR data for geothermal applications is well established. Oppliger et al (2004) discuss subsidence features associated with the Brady geothermal field in Nevada. The interferograms below show the asymmetrical growth of the subsidence pattern over time in relation to the injection and production wells. If would be interesting to see these maps updated with data from the last 15 years. With continuous monitoring and more frequent updates these subsidence maps could be used to plan future well placement and optimize power production.
Left, Interferogram B - 4.78 years: 95-11-04 to 00-09-24. Each color represents 0.16 cm line-of-sight LOS distance change. A full fringe color cycle is 2.83 cm LOS or 3.07 cm vertical. Surface faults: heavy black lines. Right, Interferogram A - 2.96 years: 92-11-26 to 95-11-04 (Oppliger et al, 2004).
CCUS applications present ideal candidates for InSAR monitoring. CO2 capture via injection and storage results in an increase in subsurface pressure and resultant surface uplift. Rucci et al (2018) show a nice example from the InSalah project in Algeria where 3.8 million tons of CO2 was injected over an 8-year period. The resultant displacement map shows a two-lobe pattern and is interpreted as an example of potential fault activation. I am reminded looking at this of similar features in microseismic data with similar mechanisms.
(Left image) Average displacement rate map [mm/yr] provided by the analysis of SAR data. The black line represents the location of the fault plane inferred by a geomechanical analysis. (Right image) Amount of tensile opening of the fault plane (Rucci et al, 2018).
Overall, whilst InSAR data has been used for over 20 years in a number of geotechnical domains it is only with the newest generation of satellites and processing techniques that it will become more widely and consistently used in the energy industry. Remember, whether you make use of it or not, this data is being acquired now, over your area of interest, from orbit, at high resolution and will be repeated in a few days.
Next time I am going to talk about how InSAR might be used in unconventionals to try to address the “unbalanced mass balance” i.e. the discrepancy between seismic energy measured from microseismic data and the injection energy from the stimulation. Using public data from the MSEEL project I will show an example of the computed seismic injection efficiency and suggest ways to incorporate InSAR data.
Finally, in a new feature this week, I will be remembering some long forgotten musical gems related to the blog theme. Not wanting to be too obvious I will skip ‘Radar Love’ in favor of the classic Underworld offering from 1988, Underneath the Radar. Relive it in all its glory here.
References
Rucci, S. Cespa and A. Ferretti Reservoir Monitoring using InSAR data: Latest Advances and Future Trends Conference Proceedings, EAGE Workshop on 4D Seismic and Reservoir Monitoring: Bridge from Known to Unknown, Nov 2018, Volume 2018, p.1 – 4
D. Dubucq, L. Turon, B. Blanco, and H. Bideaud. Earth observation remote sensing for oil and gas: A new era. The Leading Edge 2021 40:1, 26-34
R. Rahmoune et al. Multitemporal SAR interferometry for monitoring of ground deformations caused by hydrocarbon production in an arid environment: Case studies from the Sultanate of Oman. The Leading Edge 2021 40:1, 45-51
G. Oppliger, M. Coolbaugh, U. of Nevada Reno. Imaging structure with fluid fluxes at the Brady Geothermal Field, Nevada using satellite interferometric synthetic aperture radar (InSAR). SEG 74th Annual Meeting, Denver, Colorado, 10-15 October 2004