InSAR for Underground Gas Storage and Solution Mining

The SkyGeo Underground Gas Storage monitoring service provides persistent reservoir risk surveillance during the brining and during operation of the underground storage site

By assessing time-dependent shape changes in InSAR data in our Antares Platform, geoscientistst and engineers can identify patterns associated with instabilities. This is a direct pathway to improve sub-surface asset management in Gas Reservoir operations

Reservoir integrity

Two important characteristics of an underground storage reservoir are its capacity to hold natural gas and the rate at which gas inventory can be withdrawn, the deliverability rate. But a new important reservoir characteristic is imposed on the industry: geomechanical integrity of the storage facility.

In most populated areas, the local population and the regulator are exercising a new and increasing level of oversight on UGS facilities. The cost of downhole monitoring is high and the resulting data typically only tell a partial story.

An ongoing InSAR service is more than a replacement of conventional leveling. By understanding radar measurements over the entire site, in a time series going back for many years, the subsidence and heave are a breathing pattern of your underground operations. With InSAR you can see what the normal pattern looks like and create an early warning system for when abnormal patterns occur.

Environmental risk management is an important topic in the Solution Mining and Underground Gas Storage Industries. There have been cases of leaks, both sub-surface and above surface) and induced seismicity. Will it ever be possible to fully prevent a failure by using remote data? We are starting to understand the predictive power of these millions of remote sensing measurements, but they require a specialist to combine data and convert that into a correct and easy-to-understand statement about the sub-surface and about safety.

UGS Monitoring benefits

Demonstrate proactive continuous control: supporting your social license to operate

Optimize deployment of expensive surveillance crews and downhole measurements

Discover new insights about time dependent risks for reservoir engineering

Gas Storage Facilities’ stability

Natural Gas fields, porous media

Depleted reservoirs in natural gas fields have the advantage of being formed by nature to contain gas. The injection and withdrawal of gas was not nature’s intention though, the storage capabilities were formed to keep the gas in. Moreover, these natural systems do not respond to cyclical loading in predictable and linear ways. By studying the footprint on the surface of the mass flows, you can deduct the lateral diffusion rates of the gas through the various parts of the reservoir through time.

If surface movements are well understood, then they can be interpreted for geomechanical instabilities and monitored closely by the operating crew on site, who inspect every detail of the field. By adding InSAR data science techniques and setting up an early warning system based on outliers in ground movement, field operation managers can locate new problem areas before they cause issues to production and come up with the right approach for mitigation.

Salt Cavern Storage stability

Salt caverns provide very high withdrawal and injection rates relative to their working gas capacity. Cavern construction is more costly than depleted field conversions, but the ability to perform several withdrawal and injection cycles each year reduces the per-unit cost of each thousand cubic feet of gas injected and withdrawn. Due to the peak pressure during withdrawal and injection rates ground movement and instability are risks that need to be adressed by the geotechnical engineering department. Underground storage in salt caverns has the highest withdrawal and injection rates, so pressure fluctuation is a factor to be reckoned and is of key importance when setting up an Early Warning System via InSAR. When monitoring surface movement, the industry has workflows and safety practices like no other. We can assist in site production up-time, by using satellite data for forecasting maintenance needs. Areas that are moving with unexpected patterns need more attention than areas where the surface is stable. If groundwater is known to play a key role in this process, we help visualize the role of groundwater better. Our engineers and geoscientists work together with you and your engineering team to make sure maintenance planning is optimized and cost can be reduced.

Converting measurements into insights

For stability evaluation of Natural Gas fields, aquifiers and Salt Caverns, we take the breathing pattern levels into consideration, as well as soils and other geotechnical influences. These factors impact both the InSAR measurements and the resulting insight. We are building up a library of relevant deformation patterns. Each gas field has several areas of higher geotechnical risk, that each require dedicated iterative assessment.

The breathing-like pattern that occurs when injecting and withdrawing gas needs to be taken into account when analysing data over time, so any map of InSAR data is useless until it is preprocessed by an expert. This expertise does not come with a simple PhD in InSAR data and a green dotted map but relies heavily on the quality of the platform used to make the analysis. As we’ve been building the World’s leading platform for over a decade now, we are certain SkyGeo’s unique Antares platform will comply to any rigorous quality standard your company might have.

Iso-deformation maps

We create short term “iso-deformation” maps every time the satellite acquires an image and rank deformation in the field over the last couple of days or weeks by way of a multi-stage “traffic light” alerting system. For most customers, we typically show two different lines of sight, showing different parts of the field. These Contour Maps are different from our time series products in the sense that they do not rely on long term.

For more information on the relative merits of both these products and how they can help discover different stability issues, talk to our specialists.

Full area coverage

InSAR Stability Monitoring can provide early warning of ground movement across the entire area surrounding the field, cavern or aquifer. This warning system triggers operators when to mobilize for on-site inspection or assign other available site resource like downhole measurements. A key benefit of our system is to pre-process the InSAR data in our platform to a set of thresholding criteria for ground motion dynamics, resulting in a site-specific traffic light function. The data we share with your company seamlessly integrates with all industry standard software. A new dataset can be made available every time satellites revisit. For some locations thie required reporting frequency is monthly but other sites are monitored every couple of days.

With access to unlimited measurements, data science becomes key

SkyGeo is well known as market leader for Interferometric Synthetic Aperture Radar (InSAR) analysis to detect and measure surface movement and understand them in terms of sub-surface changes.
The underground gas storage industry is different from any other related industry because of the changes in reservoir pressure when injecting or withdrawing gas. Surface movement or geotechnical instability in the near area of a gas storage facility is a given fact due to day to day operations. The only way to monitor a gas storage facility properly is therefore blending datasets together, to join InSAR data with your operational sub-surface datasets.
That is why global market leaders in UGS trust us as their InSAR partner of choice. We pride ourselves on being world class field application engineers and we are on a mission to make InSAR the standard remote monitoring solution in the UGS industry. Regular monitoring provides detailed, wide-area information on instabilities. Our Antares platform will provide you with early warning communication when potential problems are detected.

Hundreds of customers from all over the world have been working with SkyGeo products and consultants for over a decade. Every storage site is different, and integrating with existing datasets and domain expertise is essential. This is how we’ve shown again and again there is no standard InSAR solution that fits all.

The world’s most reliable InSAR processing

At SkyGeo we know how the complex InSAR processing enginer works inside and out; we know what works well – and what doesn’t when assessing all the different aspects of the facilities’ stability. We have built our own code base to do interferometry; we do not rely on black-box third party software. We task and work with all available satellites and configure a service to optimize continuous risk monitoring and threshold criteria. Moreover, we have built a progressive rigorous process to do Quality Assurance auditing of our InSAR for UGS applications that has met the rigorous quality standards imposed by some of the largest and most demanding organizations in the world like ExxonMobil and Shell.

InSAR has helped us understand where fluid is going in the sub-surface and how and where we need to measure

– Jacob Visser / Abel-Jan Smit,

NedMag Customer Case

Mining operations traditionally result in subsidence, requiring monitoring, both for the mitigation of effects (like changing water tables) and for a better understanding of sub-surface operations. Traditionally, levelling was the standard way to measure subsidence at an interval of one to ten years, depending on the local circumstances. Recent technological developments allow for a much more frequent and much higher areal density evaluation of subsidence, without the necessity of having installed monitoring points. Satellite-based InSAR (Interferometric Synthetic Aperture Radar) presently gives a good estimate of the subsidence bowl by analyzing satellite images. InSAR can also be applied using historical satellite data, for instance to measure the surface effects of unplanned underground events. This type of pattern detection enables a new way of pro-actively monitoring mining operations.

A recent study was performed for Nedmag, where a cavern leakage caused a more rapid subsidence than normal, which could be backtracked with InSAR data and monitored on a monthly basis. For the case of the magnesium salt extraction from a large cavern cluster, we explore how the weekly sampling of surface motions with millimeter accuracy in the 20 km2 area above the caverns can be correlated with cavern convergence, assuming that the subsidence bowl volume is equal to volume of the inflow of salt. These surface dynamics data are available over long time periods. We discuss challenges originating in InSAR surface measurement point density and distribution in terms of correlation with known cavern and production parameters.

The very high resolution InSAR data service is run remotely, with monthly reporting but without any terrestrial component. Monitoring of dynamic patterns at the surface is shown to be a valuable tool to support mining operations.

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