Enhanced satellite technologies for hydrocarbon reservoir monitoring

Surface deformation monitoring can provide valuable constraints on the dynamic behaviour of a reservoir enabling the evaluation of volumetric changes in the reservoir. InSAR is one of the most promising and cost-effective techniques capable of providing high precision and high density displacement measurements over long periods of time. InSAR is now also benefitting from X-band technology, improving the prediction of reservoir performance. X-band sensors have higher resolution sensors and faster repeat acquisition rates thus providing a denser coverage of identified ground points and the ability to deliver quick updates. SqueeSAR™, the second-generation InSAR algorithm developed by TRE, is now a much improved tool for reservoir monitoring.

Monitoring surface deformation of worked reservoirs  can provide valuable information about the dynamic behavior of the subsurface. Compacting reservoirs induce surface subsidence, as well as contraction. Measuring this deformation can identify non-depleted compartments, detect fault reactivation, mitigate risks associated to well failure, constrain geo-mechanical models and aid field management decisions. Furthermore, surface subsidence monitoring is a legal requirement for hydrocarbon extraction in a number of countries.

Technologies most frequently used for surface deformation monitoring include: GPS, optical leveling, tiltmeters and InSAR (Interferometric Synthetic Aperture Radar).  InSAR is the only technology that provides high measurement point densities over wide areas without the need for extensive ground-based surveys, but whilst also remaining cost effective.

Apart from the spatial resolution of available satellite data and the algorithm used for processing, the quality of InSAR analyses strongly depends on the number of satellite images: the larger the dataset, the more effective the estimation and removal of any disturbances, hence the better the estimation of surface displacement.

Today, new X-band satellite missions (namely TerraSAR-X and the COSMO-SkyMed satellite constellation) are operational and guarantee very short revisiting times over an area of interest as well as a higher spatial resolution compared to older satellites mounting C-band and L-band sensors.

To accurately detect ground movement displacements a minimum number of satellite images must be processed. The characteristic short repeat cycles of X-band satellites (11 days for TerraSAR-X and 8 days for COSMO-SkyMed constellation) means that meaningful results can be achieved within only 6 months of continuous data acquisition. The increased temporal sampling rate of X-band satellites is proving extremely useful for monitoring projects, tracking seasonal trends in surface deformation as well as detecting abrupt changes in reservoir regime - allowing for fast counter-reactive responses if needed. Also, with a higher ground resolution and sensitivity to ground displacements X-band sensors provide more measurement points per square kilometer and denser displacement time-series.

TRE is capable of processing all currently available SAR data: C-band (ERS 12, ENVISAT and RADARSAT-1/2), L-band (ALOS-PALSAR) and the new X-band platforms (TerraSAR-X and Cosmo-SkyMed), thus offering InSAR products tailored our users' needs.

In conclusion: short repeat cycles and an increased number of ground measurement points enable a superior determination of ground surface movements, related to reservoir operations.

The acronym InSAR actually includes a variety of techniques that are provided by different companies worldwide. Among them is the PSInSAR™ algorithm, which appeared in 1999 as a significant evolution of conventional InSAR and was licensed to TRE. The innovation was comprised of the  identification of stable reflectors within the reflected signal, referred to as "Permanent Scatterers" or PS.  PS are points on the ground that consistently return stable signals to the satellite sensor, allowing ground displacement velocities to be measured with millimetre accuracy. They typically correspond to man-made structures such as buildings, bridges, dams, water-pipelines, antennae, as well as stable natural reflectors (e.g. exposed rocks).

After PSInSAR™, similar algorithms have been developed.  Today, TRE is launching SqueeSAR™, which represents a further breakthrough in InSAR and Earth observation capabilities.

SqueeSAR™ has an unprecedented ability to analyse ground displacements over areas with poor levels of PS (i.e. areas with low reflectivity) thanks to the additional ability to identify a new set of ground targets: 'Distributed Scatterers' or DS. DS typically correspond to debris flows, outcrops, non-cultivated lands and desert areas.

It is also important to highlight that the core of the PSInSAR™ processing chain is maintained and used within the SqueeSAR™ algorithm: the result is an enhancement of our information output capacity, meaning PS plus DS, gaining a more effective insight into ground deformation and associated surface movements.

The Oil&Gas industry is taking advantage of the increased capability of monitoring extra-urban areas where they usually operate. A higher density of measurement points (provided by the new algorithm SqueeSAR™) means that the ground surface response to changes at the reservoir layer can be analyzed with even higher accuracy and can be detected quicker. This also has positive implications for the detection and location of seismic fault reactivation, whatever the nature of field operation: oil extraction, gas storage, EOR, or CCS.

The capability of processing multi-platform data and providing pioneering techniques are TRE's main characteristics. For ten years, TRE's commitment has been to develop InSAR technology by investing in R&D, thus opening new perspectives and applications for satellite data analysis.

A Middle-East hydrocarbon reservoir: PSInSAR™ for monitoring horizontal and vertical surface deformation ^
We present a study of PSInSAR™ data over a stacked carbonate reservoir in the Middle East.

The top reservoir is a mature gas reservoir at a depth of approximately 750 m, which is known to compact. The lower reservoir is an oil reservoir at 1200 m depth that is produced by water-flood. Both reservoirs are intersected by a major graben fault, as well as numerous additional extensional faults.  Approximately 500 producer and injector wells are drilled in the area such that mitigating large-scale well failure is a business driver.

The area of interest is favorable for the application of PSInSAR™ analysis. A comparison with existing GPS data over the same field showed a good agreement for both the vertical and the horizontal components of local displacement: PSInSAR™ was thereby proven suitable for monitoring surface deformation with high accuracy.  The data showed an area of strong uplift in a shallow region in the South-East of the field.

By comparing PSInSAR™ data with known faults at reservoir level, an intriguing correlation became evident between the fault system and the gradient of the subsidence field.  Furthermore, the inverted dataset also appears  to be bounded by known faults in some areas. A comparison of the inverted dataset with pressure change maps (from a reservoir simulation) shows a strong agreement between predicted and estimated pressure changes.

Figure: the image highlights the gradient field of the cumulative vertical deformation over the observed time interval. Red areas indicate rapid changes in surface deformation velocity and are likely to correspond to active faults or fractures in the overburden. The study area is about 80 square km

⁽^⁾ Source:H. Klemm¹, I. Quseimi², F. Novali³, A. Ferretti³, A Tamburini³. "Monitoring horizontal and vertical surface deformation over a hydrocarbon reservoir by PSInSAR™", to be published in First Break magazine.

¹ Shell International Exploration & Production B.V.

² Petroleum Development Oman LLC

³ Tele-Rilevamento Europa, T.R.E. S.r.l.

The company

Tele-Rilevamento Europa - T.R.E. (TRE) was established in 2000 as the first spin-off company of the Politecnico di Milano (POLIMI) technical university and has exclusive worldwide rights to the PSInSAR™ technique. Today it also provides SqueeSAR™ - a unique innovation in InSAR analysis and Earth observation capabilities, confirming TRE as the 'icebreaker' of SAR interferometry.

TRE, together with the research group at POLIMI, is now the largest worldwide group specialized in InSAR data processing. A team of over 30 staff combines skills in Radar signal processing, GIS, Information Technology, Engineering Geology and Civil Engineering. In 2008, TRE also opened a subsidiary, TRE Canada Inc., in Vancouver, Canada, to provide services for the North American market.

Contact details:

Tele-Rilevamento Europa T.R.E. Srl
Via Vittoria Colonna, 7
20149 Milano - Italy
Tel. +39.02.4343121
www.treuropa.com
TRE Canada Inc.
#550-409 Granville Street