NPA Satellite Mapping
Location: Texas, USA
Solution by InSAR
CHALLENGE
Sinkholes pose an ever-present
danger to communities, infrastructure and oil and gas operations in
the USA. A visible sinkhole is often
the tip of the iceberg compared
to the wider region that has the
potential to collapse. A solution is
required to map both precursor and
post-collapse deformation associated with these hazards.
SOLUTION
Using a combination of optical
satellite imagery and InSAR, we
map sinkhole features and localized
deformation to infer the extent and
magnitude of the hazard, providing an essential input into planning,
risk assessment and remediation
activities.
CONCLUSION
The results show subsidence of
surrounding areas can continue
for at least 35 years after sinkhole
formation, underlining the ongoing risk of further impacts to land,
infrastructure and potentially life.
InSAR can help to identify areas
at risk of future sinkhole formation, with precursor signals at Wink
detectible at least nine years before
collapse occurred.
This case study provides evidence
of how low-cost InSAR mapping
can be used to remotely monitor
large regions for sinkhole hazards,
reducing the financial, logistical
and safety risks associated with
conventional surveying.
cgg.com/npa
REVEALING HIDDEN
SINKHOLE HAZARDS
Regions prone to sinkhole formation can often be identified. However, prediction
of exact sinkhole locations and timing of formation are exceedingly difficult. This
case study from Wink, in the Permian Basin of Texas, demonstrates how InSAR
can measure both precursor and post-collapse deformation associated with
sinkhole hazards to support risk assessment and mitigation.
BACKGROUND
Sinkholes (also known as dolines) are a hazard across
many parts of the world. They are commonly the result
of karst dissolution processes in areas underlain by
carbonates or evaporites. However, they may also be
caused by suffosion or piping of sediment, or collapse
of existing void spaces. Although most sinkholes occur
naturally, others can be caused or influenced by human
activity, for example water leaks, collapse of abandoned
mine workings, and oil and gas production activities.
1a
1980
The Permian Basin, spanning Texas and New Mexico, is
currently the highest oil-producing region in the United
States1. It contains large deposits of Palaeozoic evaporites;
dissolution of these in contact with groundwater can
result in a susceptibility to sinkhole formation2.
CHALLENGE
Prediction of sinkhole locations and occurrences is
extremely challenging. However, owing to potential risks
to lives and property there are obvious benefits to any
advanced warning of these hazards. This is certainly true
within the oil and gas industry, where subsurface cavities
that lead to sinkholes can cause wellbore integrity issues,
loss of drilling mud and can contain flammable gas.
Sinkholes are difficult to map using conventional survey
techniques due to uncertainties over their location, as well
as the financial and logistical risks associated with field
work. They can also be challenging to detect using InSAR,
particularly those occurring over small scales, or with fast
or strongly variable subsidence rates. Furthermore, some
sinkholes have been shown not to exhibit precursory
subsidence, instead occurring as a sudden collapse.
However, high-resolution synthetic aperture radar
(SAR) sensors introduced over the past decade have
expanded capabilities to enable monitoring of smaller
sinkholes. Along with more frequent sampling, and longer
wavelength radar data, they also assist in capturing high
deformation gradients over short distances.
Understanding ground deformation signals, and the
processes which affect the progression and timing of
sinkhole development, is key for understanding and
mitigating these hazards.
This case study explains how InSAR has been used to map
sinkhole subsidence in the Permian Basin town of Wink.
1992 - 2001
1b
1980
2002
2002 - 2010
Figure 1a. Optical imagery from 1996
showing the first sinkhole which formed in
1980. Figure 1b. Optical imagery from 2015
showing the second sinkhole which formed
in 2002, 1.5km to the south. Images © CGG.
Optical imagery © USGS.
SINKHOLE MAPPING - Texas, USA – Solution by InSAR
SOLUTION
InSAR has previously been used to successfully detect subsidence around a number of existing
sinkholes3,4. In a number of locations, archive InSAR studies have also revealed precursor subsidence
signals, prior to sinkhole formation. InSAR therefore has the potential to detect precursor subsidence
which may correlate with sinkhole formation, identifying locations of high potential risk.
2a
1980
Two sinkholes occurred around 3.5km to the northeast of the town of Wink; one in June 1980, and a
second in May 2002 (Figs. 1a & 1b). The 1980 sinkhole has a diameter of approximately 100m. The 2002
sinkhole opened around 1.5km to the south, with initial dimensions of 150m by 100m, and has since
expanded to 250m by 220m. The area is underlain by the Salado salt formation, which is susceptible
to natural dissolution. Between the 1920s and 1960s, oil production and water injection took place at
a number of wells across the Hendrick oil field, in the area later affected by the two sinkholes. It has
been suggested that the older drilling technology used during that period may have resulted in well
casing integrity issues, which could have accelerated the formation of dissolution cavities5.
An archive of SAR data collected over a period of more than 20 years enables a long term perspective on
surface deformation across Wink. Unfortunately no suitable archive SAR imagery is available spanning
the formation of the sinkholes in 1980 or 2002. However, datasets are available for periods between
the two events (ERS, 1993-2000), and following the formation of the second sinkhole (ALOS PALSAR,
2007-2011). A small stack of recent SAR images from Sentinel-1A are also available, allowing an upto-date assessment of ongoing deformation, and providing an opportunity for ongoing monitoring.
2002
March 1993 to November 1993
2b
1980
Figs. 2a, 2b and 2c show wrapped interferograms from ERS, ALOS and Sentinel-1A data, showing
the variations in observed deformation (shown as colored contours) across a range of different time
periods. Three main areas of subsidence are visible; two surrounding the existing sinkholes, and an area
further to the south. Around the 1980 sinkhole, persistent subsidence features are observed in all three
periods. These are centred on the sinkhole, with a diameter of 200-600m. The 2002 sinkhole is located
towards the southwest corner of a wider area of subsidence, with extents of approximately 1 by 2km. In
addition to the moderate subsidence immediately surrounding the sinkhole, there are several locations
where even stronger subsidence is concentrated, to the north and east. Overall, rates of subsidence in
some parts of this area are up to ~80cm/yr.
Around 1.3km to the south of the 2002 sinkhole is a third area of subsidence, with an extent of around
400m. This is of lower magnitude than that surrounding the sinkholes; and the deformation appears
to be somewhat sporadic in nature. This subsidence signal is most clearly visible in the ALOS data
(Fig. 2b), with around ~14cm of subsidence observed between July 2007 and January 2011. This area
of subsidence does not correspond to any existing sinkhole, but shows temporal persistence over a
timespan of at least 15 years. It could potentially represent an area of subsurface dissolution, and
therefore be at higher risk of future sinkhole formation. However, there could be other causes for such
a signal, including ongoing oil production or water abstraction.
These results provide a clear demonstration of the ability of InSAR to measure ground deformation
related to salt dissolution and sinkhole formation. The results show subsidence of surrounding
areas can continue for at least 35 years after sinkhole formation, underlining the ongoing risk to
land, infrastructure and life. Furthermore, InSAR can help to identify areas at risk of future sinkhole
formation, with precursor signals at Wink detectible at least nine years before collapse occurred. This
offers the potential for mitigation of sinkhole hazards and the optimization of on-site investigations.
REFERENCES
- 1. U. S. Energy Information Administration, Drilling Productivity Report, (April 2016), retrieved 10/05/2016.
http://www.eia.gov/petroleum/drilling/pdf/permian.pdf
- 2. Paine, J. G., Buckley, S. M., Collins, E. W., & Wilson, C. R. (2012). Assessing collapse risk in evaporite
sinkhole-prone areas using microgravimetry and radar interferometry. Journal of Environmental and Engineering
Geophysics, 17(2), 75-87.
- 3. Nof, R. N., Baer, G., Ziv, A., Raz, E., Atzori, S., & Salvi, S. (2013). Sinkhole precursors along the Dead Sea,
Israel, revealed by SAR interferometry. Geology, 41(9), 1019-1022. doi: 10.1130/G34505.1
- 4. Jones, C. E., & Blom, R. G. (2014). Bayou Corne, Louisiana, sinkhole: Precursory deformation measured by radar
interferometry. Geology, 42(2), 111-114.
- 5. Kim, J. W., Lu, Z., & Degrandpre, K. (2016). Ongoing deformation of sinkholes in wink, texas, observed by
time-series Sentinel-1a SAR interferometry (preliminary results). Remote Sensing, 8(4), 313.
cgg.com/npa
Adam Thomas
InSAR Manager
NPA Satellite Mapping
UK
Tel: +44 1732 865023
Fax: +44 1732 866521
[email protected]
2002
July 2007 to January 2011
2c
1980
2002
August 2015 to December 2015
Figure 2a. Wrapped InSAR deformation map
derived from ERS-1/-2 data spanning March
1993 - November 1993; Figure 2b. Wrapped
InSAR deformation map derived from ALOS1 data spanning July 2007 - January 2011;
Figure 2c. Wrapped InSAR deformation map
derived from Sentinel-1A data spanning
August 2015 - December 2015. Black
circles in all maps show the location of the
sinkholes shown in Figures 1a and 1b.
© CGG 2016